The present study is a contribution to the further analysis of
the problem of adaptation of energy expenditure to uptake. Clearly,
this can not be solved by the study of total metabolic rate alone, but only by an analysis of the various components that make up this total. ...

Zie: General introduction

Westerterp, Klaas Roelof

Welsh

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   University of GroningenHow rats economizeWesterterp, Klaas RoelofIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:1976Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Westerterp, K. R. (1976). How rats economize: Energy loss in starvation. s.n.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 17-07-2023CHAPTER IGENERAL INTRODUCTIONA d u l t  a n i r n a l s ,  l i v i n g  i n  a  c o n s t a n t  b i o l o g i c a l l y  a d e q u a t e  e n v i r o n m e n t ,ma in ta i n  a  ba lance  be tween  ene rgy  up take  and  ene rgv  expend i t u re .  Thee n e r g y  s t o r e  o f  t h e  b o d y  d o e s  n o t  f l u c t u a t e  m u c h ,  a s  t h e  c o n s t a n c y  o fbody  we igh t  and  body  compos i t i on  s t r ows ,  wh i l e  t he  s to re  i s  sma l l  i nc o m p a r i s o n  t o  t h e  d a i l y  e n e r g y  t u r n o v e r ,  e s p e c i a l l y  i n  s m a l l  a n i m a l s .T h i s  c a n  b e a c l . i e v e ' J  e i t h e r  b y  c o n t r o l  o f  t h e  u p t a k e  o r  t h e  e x p e n d i t u r eo f  e n e r g y .Tha t  an  an ima l  adap t s  i t s  up rake  t o  t he  expend i t u re  o f  ene rgy  i swe i l  known .  S tud ies  on  t h i s  po in t  we re  done  by  man ipu la t i ng  ene rgy  ex -pend i t u re  v i a  a  change  o f  env i r onmen ta l  t empe ra tu re  o r  v i a  t he  amoun to f  a c t i v i t y  i m p o s e d  o n  t h e  a n i m a l .  C o r t l e  a n d  C a r l s o n  ( 1 9 5 4 )  i n c r e a s e dt h e  e n e r g y  e x p e n d i t u r e  i n  r a E s  b y  l o w e r i n g  E h e  e n v i r o n m e n t a l  t e m p e r a -t u re  f r om 25o  C ,  a  va l ue  i n  o r  c l ose  t o  t he  t he rmoneuL ra l  zone  o f  t hese. - o ^an ima l s ,  t o  5 "  C .  An ima l s  p l aced  i n  t h i s  co l d  env i r onmen !  a te  tw i ce  asmuch  as  t he i r  con t ro l s  i n  t he  wa rm env i r onmen t .  Maye r  e t  a l .  ( 1954 )  ex -e r c i s e d  r a t s  i n  a  t r e a d m i l l  w i t h  a  s p e e d  o f  o n e  m i l e  p e r  h o u r .  T h e  a n i -ma l s  p rac t i ca l l y  doub led  t he i r  f ood  i n t ake  when  t he  du ra t i on  o f  exe r -c i se  was  i nc reased  f r om one  t o  s i x  hou rs  pe r  day ,  wh i l e  bod . v  we igh t  wasma in ta i ned .  The  measu red  changes  o f  f ood  i n t ake  we re  rep resen ta t i ve  f o re n c r g y  r . r p t a k e  b e c a u s e  i n  a d u l t  r a t s  i m p o r t a n t  c h a n g e s  o f  d i g e s r i o n  e f -f i c i ency  i n  r e l a t i on  t o  l he  l eve l  o f  f ood  i n t ake  a re  neve r  f ound( N e h r i n g  e t  a l . ,  1 9 5 9 ) .  I n  b o t h  e x p e r i m e n E s  m e n t i o n e d  a  b a l a n c e  b e t w e e nup take  and  expend i t u re  was  reached  aga in  unde r  t he  new  c i r cums tances  asshown  by  t he  cons tancy  o f  body  we igh t  du r i ng  more  t han  one  week .  Mo re -ove r ,  t he  s i ze  o f  t he  rese rves  was  p robab l y  no t  i - n f l uenced  because  t h i sbody  we igh t  had  t he  no rma l  va l ue .To  conc lude ,  an  an ima l  can  change  i t s  ene rgy  up t . ake  w i t h  a t  l eas ta  f ac to r  two  f o r  adap t i ng  i t  t o  t he  expend i t u re  o f  ene rgy .T h e  p o s s i b i L i t i r  t h a t  i t n  a n i m a l  a d a p t s  i t s  e x p e n d i c u r e  t o  t h e  u p -t a k e  o [  e n e r g y  i s  o f t e n  c a l l e d  i n  q u e s t i o n .  R e c e n L l y  L e  ] 4 a g n e n  ( 1 9 7 4 )c v c n  s L A L ( ' d  t l ) a t  L I ) e  (  L \ t ) t r r r l  d f  c n c r q y  o x p e n d i t u r e  i s  c ( , n L r ; r r y  t o  w h a Lb o d y  v i e i g h t  w o u l c i  r e q u i r e  i n  v i e w  o f  h y p e r a c t i v i t y  i n  f o o d  d e p r i v a t i o na n d  h y p o a c t i v i t y  i n  o b e s i t y .  l n v e s t i g a t i o n s  o n  t h i s  p o i n L  a v a i l a b L e  i nt h e  l i t e r a t u r e  i n v o l v e d  e i t h e r  p a r t i a l  ( K e y s  e t  a L . ,  1 9 5 0 ;  G r a n d e  e ti r 1 . ,  l 9 5 B ;  M e y e r  a n d  C l a w s o n ,  1 9 6 4 ;  l " l a l k t ' r  a n d  t l a r r e t t ,  I 9 7 0 ) ,  o r  L r o m -p l e t e  ( C u m n r i n g  a n d  M o r r i s o n ,  1 9 6 0 ;  K l e i b e r ,  l 9 6 l ;  l l o r r i s o n ,  l 9 6 B )  f o o dd e p r i v a L i o n  o r ,  o n l y  i n  m a n ,  r a i s i n g  o f  i n t a k e  b y  o v e r f e e d i n g  ( l { i 1 l e rc n d  l ' 4 u m I o r d ,  1 9 6 7 \ ,  I n  t l r e s c  e x p e r i r n c n L s ,  c o n L r . l r y  t r r  t h o s e  i n  w h i e  he x p e n d i t u r e  w a s  m a n i p u l a r e d ,  b o d y  w e i g h t  d i d  n o t  r e m a i n  a !  t h e  e q u i l i -b r i u m  1 e v e 1  f o r  a d  l i b i t u m  c o n d i t i o n s .  A  n e w  b a l a n c e  b e t w e e n  i n t a k e  a n de x p e n d i t u r e  w a s  r e a c h e d  o n l y  s o m e t i m e s  ( K e y s  e t  a 1 . ,  \ r l a l k e r  a n dG . 3 r r e t t ,  l . c ,  ) .  T l r e s e  f e c L s  c o m p l  i c a L e  t h e  i n L . " r p r e t i r I i o n  o t  L l ) c  r e -s u l t s  w i E h  r e s p e c t  t o  t h e  q u e s t  i . r n  o [  r : . :  '  :  . '  .  . r t .  i ' :  , r .  , . :  -l ; , i , t t s .  S o m e  m e t a b o l i c  s a v i n q s  w i l l  r e s u l t  f r o n  t h e  m e r e  f a c t  t h a t  t h e*u n d e r I e d  s u b j e c t " ' h a s  t o  h a n d l e  a n d  d i q e s t  l e s s  f o , r d  ] l r r r € o v € r ,  d u r i n gn ; t r l  i a l  r r r  c o n r r r l p l e  l  - - : " ^ r :  -  ' !  -  t  o l r r c , r o a n  . r n d  l e T  , r r  p r / o n  n l r t <r \  L r  u i H r  r  r ( u r r s  5 ! \ \ v F (o f  t h e  c e l  l s  t h e m s e l v e s  a r e  u s e d  a s  f u e l .  B o d y  m a s s  w i l  I  d e c r e a s e ,  a n dr h i s  i s  b o u n d  t o  c 3 u s e  d  d r o p  i r L  m e L a b o l i s m .  H o w e v e r ,  I o L l o w i n g  C u m m i n ga n d  l l o r r i s o n  ( 1 . c . ) ,  T  w i L l  n o t  c e l l  r h e s e  d e . . r e a s e s  t a d e p t i v e t .R a t h e r .  I  a m  i n c l i n e d  t o  r e s t r i c t  t h i s  t e r n  t o  t h e  c a s e  w h e r e  L h e  u n -d e r I e d  a n i r n a l  s p e n d s  I c s s  f r e e  e n e r g y  o n . r  g i v e n  I u n c t i o n  ( e . g .  p r o L e i nE u r n o v e r ,  o r  m u s c u l a r  e f f o r t  f o r  a  g i v e n  b e h a v i o u r )  t h a n  a n  a d  l i b i c u mf  ed  conspec i f  i c  t -  L i t e  se t l v  r t t : t g i 1 |  and  body  , - , c rT i r t r s r l  l . i ' r r r  wou ld  do  (p .71 ) .I f  t h i s  p h e n o m e n o n  c o u l d  b e  s h o \ r n  t o  e x i s t ,  a  b a s i s  w o u l d  t h e r e b y  b el a i d  f o r  t h e  v i e w  t h a t  e v o l u t i o n  h a s  p r o v i d e d  t h e  i n d i v i d u a l  w i t h  a^ - ^  - :  ^ 1  ^ ^ . . ^ L :  r :  + "  r f  e k i  n s  o u t  i  t s  n r o v i s i o n s  i n  o r d e r  L o  i n c r e a s e  L h eL d P a u ,  r l L y  u r  l L J  t s l uc h a n c e  L h a t  i t  m a y  t i d e  o v e r  t e m p o r c r y  t o o d  s c e r c i r y ,  a  c o n d i t i o nx_." T h i s  d i s c u s s i o n  e m p h a s i s e s  t i r e  c a s e  o f  u n d e r f e e d i n g ,  s i n c e  t h i s  i s  t h eo n l y  c o n d i t i o n  u s e d  i n  m y  e x p e r i m e n t s .  A n  a n a l o g o u s  d e f i n i t i o n  o f ' a -d a p t a t i o n  o f  e x p e n d i t u r e  t o  u p t a k e '  c a n  b e  f o r m u l a t e d  f o r  t h e  c a s e  o fo v e r f e e d i n e .co f i non  i n  t he  na tu ra l hab i t a t  o f  many  spec ies .  Howeve r ,  such  a  de f i n i -t i o n  o f  a d a p t i v e  r e s ! r i c t i o n  o f  e x p e n d i t u r e  i n v o l v e s  f o r m i d a b l e  o p e r a -t i o n a l  d i f f i c u l t i e s .  I  s h a 1 l  r e E u r n  t o  s o m e  a s p e c t s  o f  t h i s  p r o b l e m s  i nc h a p t e r  8 .  F o r  t h e  m o m e n t  i t  w i l l  s u f f i c e  t o  s t a t e  t h a t  c o n c l u s i o n s  i nt he  t i ce ra tu re  a re  no t  unan imous  as  t o  r he  ques t i on  whe the r  o r  no tc h a n g e s  i n  m e t a b o l i s m  c a u s e d  b y  m a n i p u l a t i o n  o f  f o o d  i n L a k e ,  c a n  b ea c c o u n t e d  f o r  e x c l u s i v e l y  i n  t e r m s  o f  c h a n g e d  b o d y  m a s s  a n d  c e s s a t i o no f  f o o d  p r o c e s s i n g .  C u m m i n g  a n d  M o r r i s o n  ( 1 9 6 0 )  s t a t e :  ' T h e  t o t a l  e n e r -g y  e x p e n d i r u r e  o . [  L h e  r a t s  I e 1 I  d u r i n g  t h e  4 B  h r  f a s t  a n d  r o s e  d u r i n gre feed ing .  L t r en  t he  changes  i n  body  we ighc  and  f ood  i n t ake  we re  a l l owedfo r ,  t he  me tabo l i c  r a te  was  f ound  t o  r ema in  cons tan t  t h roughou t  t hew h o l e  e x p e r i r n e n t a l  p e r i o d t ,  I n  c o n t r a s t ,  W a l k e r  a n d  G a r r e t t  ( 1 - o 7 0 )c o n c l u d e  t h a t  e v e n  a f t e r  c o r r e c t i o n  f o r  b o d y  s i z e  r e d u c t i o n ' t h e  e n e r g yexpend i t u re  dec l i ned  marked l y  as  t he  pe r i od  o f  unde rnu t r i t i on  was  p ro -l o n g e d ' .  ( T h e y  d i d  n o t  t a k e  i n t o  a c c o u n t  c h a n g e d  c o s t s  o f  f o o d  p r o c e s -s i n g ,  b u t  E h i s  e f f e c c  w i l l  b e  c o r ) . s t a n t  f r o m  a b o u t  t h e  s e c o n d  d a y  o n -n a r d s ,  w h e r e a s  t h e  d e c r e a s e  c o n t i n u e d  b e y o n d  t h a t  t i m e , )T h e  p r e s e n t  s E u d y  i s  a  c o n t r i b u t i o n  t o  t h e  f u r t h e r  a n a l y s i s  o ft h e  p r o b l e r n  o f  a d a p t a t i o n  o f  e n e r g y  e x p e n d i t u r e  t o  u p E a k e .  C l e a r l y ,t h i s  c a n  n o t  b e  s o l v e d  b y  t h e  s t u d y  o f  t o t a l  m e t a b o l i c  r a l e  a l o n e ,  b u ton l y  by  an  ana l ys i s  o f  t he  va r i ous  componen ts  l ha t  make  up  t h i s  t o t a l .C u s t o m a r i l y  f o u r  c o m p o n e n t s  a r e  d i s t i n g u i s h e d  i n  t h e  e n e r g y  r n e t a b o l i s mo f  a  h o m e o t h e r m  ( G e s s a m a n ,  1 9 7 3 ) :  b a s a l  m e t a b o l i s m ;  m e t a b o l i s m  a b o v et h e  b a s a l  l e v e l  w h i c h  i s  u s e d  f o r  t h e r m o r e g u l a t i o n ;  m e t a b o l i s m  a s s o c i a -t e d  w i t h  a c t i v i t ' 1 ;  a n d  m e t a b o l i c  p r o c e s s e s  i n v o l v e d  i n  t h e  d i g e s t i o n  o ff o o d .  I  s h a l l  u s e  t h e  s a m e  d i v i s i o n .  H o w e v e r ,  i t  s h o u l d  b e  p o i n r e d  o u tt ha t  wha t  I  can  rneasu re  i n  my  expe r imen ts  i s  no t  t he  ra te  o f  ene rgye x p e n d i t u r e  e . g .  o n  t h e  p r o c e s s  o f  p e r f o r m i n g  m u s c u l a r  a c t i v i E y ,  b u ton l y  t he  d i f f e rence  i n  meuabo l i c  r a te  be tween  t he  pe r i od  du r i ng  wh i chtha t  ac t i v i t y  t akes  p l ace  and  pe r i ods  i n  wh i ch  t he  an ima l  i s  no t  en -g a g e d  i n  m u s c u l a r  a c E i v i t y .  T h i s  d i f f e r e n c e  g i v e s  r h e  c o s t  o f  a c r i v i r yon l y  i f  t he  o the r  componen ts  o f  ene rgy  expend i t u re  ( d i ges t i on  and  o the rp r o c e s s e s  i n  r e s L i n g  m u r a b o i i s m )  p r o c c e d  a t  r l r e  s J m e  r a L c  i r r e s p e c L i v eo f  t h e  o c c u r r e n c e  o f  r n u s c u l a r  a c t i v i t y .  T  h a v e  n o  m e a n s  o f  a s c e r t a i n i n gw h e t h e r  t h i s . i s  : ; o ,  b u t  i t  s e e m s  l r i g h l v  d o u h t f u l  f o r  i n s t a n c e  i n  v i e wn L  I h e  e f f e ,  t s  o I  s y m p a t h e r i . '  d i s c l r a r g e  a n d  e J r e n o m e d u l  l a r y  s e c r e t i o nc a u s i n g  s p l a n c h n i c  v a s c u l a r  c o n s t r i c t i o n ,  i n l r i b i t i o n  o f  l i p o g e n e s i s ,e t c .  I n  p r i n c i p l e  t h e r t f o r e  I  c e n  s t . r t e  o n l - v  t h e  d i f f e r e n c e  i n  m e t a b o -l i c  r : a t e  b e t w e e n  t h e  f  o L l o \ ^ / i n g  , ' . ) / r r 1 1 .  f . i : r t t s : .  l )  a n i m a l  r e s t i n g  i n  t h e  p o s t; r b s o r p t i v e  s L a t c ,  2 )  e n i m a l  r e s r i n g  r n d  p r o (  e s s i n g  f o o d .  3 )  a n i m a l  a c -t i v e .  F o r  b r e v i t y ,  h o w e v e r ,  I  s h a l l  d i s c u s s  m _ v  r e s u l t s  i n  t e r m s  o f  ar e s t i n g ,  a  f o o d  p r o c e s s i n g ,  s n d  - - L n  e c t i v i t y  , z o n r t ' t '  ) t ' +  c r f  m e t a b o l i s m  (( s e e  a l s o  p . 6 5 ) .  T h e  p o s s i b l e  i n f l u e n c e  o f  L h e  d e m a n d s  o f  t h e r m o r e g u l a -t i o n  o n  m e t a b o l i c  r a L c  c o u l d  b e  s t u d i e d  i n  p r i n c i p l . ' b y  m a k i n g  o b s e r -v a t i o n s  a f  d i f f e r e n t  a m b i e n t  t e m p e r i r t u r e s .  F o r  i n s t a n c e  i f  t h e  a n i m a li s  p l a c e d  i n  t h e  c o l d ,  t h i s  s h o u l d  l e a d  t o  a n  i n c r e a s e  i n  o n e  o r  m o r eo f  t h e  o L h e r  L l r r e e  c o m l ) o n e n t s  o f  m c t l b o l i s m .  S u e l r  r e m p e r d t u r e  c x p e r i -m e n L s ,  h o w e v e r ,  f e l l  o u t s i d e  t h e  s t ' o p e  o I  t h e  p r e s e n t  s t u d y .T h e  l a b o r a t o r y  r e t  w a s  c h o s e n  a s  t h e  s r r h . i e c t  o f  m v  e x p e r i m e n t s  b e -c a u s e  i t  i s  c o m m o n l y  u s e d  i n  s t u d i e s  o n  c a l t r r i c  r e g u l a c i o n .  I n t a k e  w a sc h a n p e d  i n  o n e  d i  r e c t  i , r n  n n l v  n A h p l v  r e d r r c f i o n -  A l  I  e r n c r i m e n t s  w e r eJ  t  r r s i ' r \d o n e  a t  t h e  s a m e  t e m p e r a t u r e  i n  t h e  t h e r m o n e u t r a l  z o n e  o f  f h e  r a t s  f o rE w o  r e a s o n s ,  F i r s E ,  I  w i s h e d  ! o  a v c i d  t h e  c o n r p l i c a t i o n  o f  s p e c i a l  ( a n dn o t  d i r e c t l y  m e a s u r a b l e )  h e a t  p r o d u c t i o n  f o r  t h e r m o r e g u l a t i o n .  S e c o n d ,e x p e r i m e n t s  w i t h  f o o d  d e p r i v e d  a n i m a l s  c a n  b o  c o n t i n u e d  l o n g e r  w i  t h o u tl p f h a l  p f I p c t s -  f o r  a L  t e m n e r a t u r ( , s  i n  o r  n e a r  l l r e  L h e r m r . n e u t r a l  z o D ea n i m a l s  c a n  r n o b i l i z e  m o r e  o f  t h e i r  e n e r g y  s t u r e s  a s  s h o w n  b y  d a t a  o nb i r d s  ( K e n d e i g h ,  1 9 4 5 )  a n d  r a t s  ( K l e i b e r ,  1 9 4 5 )  s t a r v e d  t i l l  d e a c h  a td i f f e r e n t  t e m p e r a t u r e s ,  C o n s e q u e n t l y  i n  m y  e x p e r i m e n t s ,  n o t w i t h s t a n d -i n g  l o n g  p e r i o d s  o f  f o o d  d e p r i v a t i o n ,  o n l v  t w o  o u t  o f  m o r e  t h a n  o n eh u n d r e d  a n i m a l s  d i e d :  t h e  o t h e r : s  c o u l d  b e  r e f e d .T h e  e n e r g y  e x p e n d i t u r e  w a s  m c a s u r e d  b y  t w  m e t h o d s :  l )  a  b a l a n c et e c h n i q u e  ( c h a p t e r  3 ) ,  c a l c u l a t i n g  e x p e n d i t u r e  f r o m  f o o d  i n t a k e ,  f a e c e sp r o d u c t i o n  a n d  c h a n g e s  i n  b o d y  r e s e r v e s ,  a n d  2 )  i n d i r e c L  c a l o r i m e t r y ,c a l c u l a t i n g  e x p e n d i t u r e  f r o m  t h e  g a s  e x c h a n g c  o f  t h c  a n i m a l s  ( c h a p r e r st4 -7 ) .  By  i nc reas ing  t he  t empo ra l  r eso lu t i on  o f  t he  l a t t e r  me thod  andcomb in i ng  i t  w i t h  o the r  r echn iques  a  de ta i l ed  ana l ys i s  o f  t oLa l  expen -d i t u r e  i n t o  i t s  c o m p o n e n t s  w a s  m a d e  p o s s i b l e ,  T h i s  p r o c e c i u r e  w i l l  b ed e s c r i b e d  i n  d e L a i l  i n  c h a p t e r  2 .I  f i r s t  de te rm ined  t he  change  i n  t o t . a r  expend i t u re  du r i ng  f ooddep r i va t i on  ( chap re r  3 ) ,  Th i s  change  \ ^ / as  f u r t he r  ana l ysed  i n  t e rms  o ft h e  e n e r g e t i c  c o n s e q u e n c e s  o f :  l )  t h e  c e s s a E i o n  o f  f o o d  p r o c e s s i n g( c h a p t e r  4 ) ; 2 )  c h a n g e s  o f  a c r i v i r y  ( c h a p t e r  5 ) ;  a n d  3 )  c h a n g e s  o ff a s t i n g  r e s t i n g  m e t a b o l i c  r a t e  ( c h a p t e r  5 ) .  F i n a l l y  t h e  c o n s e q u e n c e so f  t he  expend i t u re  changes  f o r  r egu la t i on  o f  body  t empe ra tu re  we res t u d i e d  ( c h a p t e r  7 ) .  w i t h  r e s p e c t  t o  t h e  f i r s t  p o i n r  i u  i s  r e g r e t t a b l etha t  t he  ene rgy  expend i t u re  on  f eed ing  behav iou r  cou ld  no t  be  sepa ra -red  f r om Lha t  on  o the r  behav iou r .  The re fo re  my  es t ima te  o f  t he  ene rgye x p e n d i t u r e  a s s o c i a r e d  w i t h  f o o d  p r o c e s s i n g  i n c l u d e d  o n l y  t h e  c o s t s  o fi n t e rna l  p r : ocess ing ,  wh i l e  f o r  i ns tance  f ood  hand l i ng  was  measu red  t o -ge the r  w i t h  t he  cos t s  o f  non - f eed ing  behav iou r .

How rats economize:Energy loss in starvation

   University of GroningenHow rats economizeWesterterp, Klaas RoelofIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:1976Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Westerterp, K. R. (1976). How rats economize: Energy loss in starvation. s.n.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 04-06-2022CHAPTER IGENERAL INTRODUCTIONA d u l t  a n i r n a l s ,  l i v i n g  i n  a  c o n s t a n t  b i o l o g i c a l l y  a d e q u a t e  e n v i r o n m e n t ,ma in ta i n  a  ba lance  be tween  ene rgy  up take  and  ene rgv  expend i t u re .  Thee n e r g y  s t o r e  o f  t h e  b o d y  d o e s  n o t  f l u c t u a t e  m u c h ,  a s  t h e  c o n s t a n c y  o fbody  we igh t  and  body  compos i t i on  s t r ows ,  wh i l e  t he  s to re  i s  sma l l  i nc o m p a r i s o n  t o  t h e  d a i l y  e n e r g y  t u r n o v e r ,  e s p e c i a l l y  i n  s m a l l  a n i m a l s .T h i s  c a n  b e a c l . i e v e ' J  e i t h e r  b y  c o n t r o l  o f  t h e  u p t a k e  o r  t h e  e x p e n d i t u r eo f  e n e r g y .Tha t  an  an ima l  adap t s  i t s  up rake  t o  t he  expend i t u re  o f  ene rgy  i swe i l  known .  S tud ies  on  t h i s  po in t  we re  done  by  man ipu la t i ng  ene rgy  ex -pend i t u re  v i a  a  change  o f  env i r onmen ta l  t empe ra tu re  o r  v i a  t he  amoun to f  a c t i v i t y  i m p o s e d  o n  t h e  a n i m a l .  C o r t l e  a n d  C a r l s o n  ( 1 9 5 4 )  i n c r e a s e dt h e  e n e r g y  e x p e n d i t u r e  i n  r a E s  b y  l o w e r i n g  E h e  e n v i r o n m e n t a l  t e m p e r a -t u re  f r om 25o  C ,  a  va l ue  i n  o r  c l ose  t o  t he  t he rmoneuL ra l  zone  o f  t hese. - o ^an ima l s ,  t o  5 "  C .  An ima l s  p l aced  i n  t h i s  co l d  env i r onmen !  a te  tw i ce  asmuch  as  t he i r  con t ro l s  i n  t he  wa rm env i r onmen t .  Maye r  e t  a l .  ( 1954 )  ex -e r c i s e d  r a t s  i n  a  t r e a d m i l l  w i t h  a  s p e e d  o f  o n e  m i l e  p e r  h o u r .  T h e  a n i -ma l s  p rac t i ca l l y  doub led  t he i r  f ood  i n t ake  when  t he  du ra t i on  o f  exe r -c i se  was  i nc reased  f r om one  t o  s i x  hou rs  pe r  day ,  wh i l e  bod . v  we igh t  wasma in ta i ned .  The  measu red  changes  o f  f ood  i n t ake  we re  rep resen ta t i ve  f o re n c r g y  r . r p t a k e  b e c a u s e  i n  a d u l t  r a t s  i m p o r t a n t  c h a n g e s  o f  d i g e s r i o n  e f -f i c i ency  i n  r e l a t i on  t o  l he  l eve l  o f  f ood  i n t ake  a re  neve r  f ound( N e h r i n g  e t  a l . ,  1 9 5 9 ) .  I n  b o t h  e x p e r i m e n E s  m e n t i o n e d  a  b a l a n c e  b e t w e e nup take  and  expend i t u re  was  reached  aga in  unde r  t he  new  c i r cums tances  asshown  by  t he  cons tancy  o f  body  we igh t  du r i ng  more  t han  one  week .  Mo re -ove r ,  t he  s i ze  o f  t he  rese rves  was  p robab l y  no t  i - n f l uenced  because  t h i sbody  we igh t  had  t he  no rma l  va l ue .To  conc lude ,  an  an ima l  can  change  i t s  ene rgy  up t . ake  w i t h  a t  l eas ta  f ac to r  two  f o r  adap t i ng  i t  t o  t he  expend i t u re  o f  ene rgy .T h e  p o s s i b i L i t i r  t h a t  i t n  a n i m a l  a d a p t s  i t s  e x p e n d i c u r e  t o  t h e  u p -t a k e  o [  e n e r g y  i s  o f t e n  c a l l e d  i n  q u e s t i o n .  R e c e n L l y  L e  ] 4 a g n e n  ( 1 9 7 4 )c v c n  s L A L ( ' d  t l ) a t  L I ) e  (  L \ t ) t r r r l  d f  c n c r q y  o x p e n d i t u r e  i s  c ( , n L r ; r r y  t o  w h a Lb o d y  v i e i g h t  w o u l c i  r e q u i r e  i n  v i e w  o f  h y p e r a c t i v i t y  i n  f o o d  d e p r i v a t i o na n d  h y p o a c t i v i t y  i n  o b e s i t y .  l n v e s t i g a t i o n s  o n  t h i s  p o i n L  a v a i l a b L e  i nt h e  l i t e r a t u r e  i n v o l v e d  e i t h e r  p a r t i a l  ( K e y s  e t  a L . ,  1 9 5 0 ;  G r a n d e  e ti r 1 . ,  l 9 5 B ;  M e y e r  a n d  C l a w s o n ,  1 9 6 4 ;  l " l a l k t ' r  a n d  t l a r r e t t ,  I 9 7 0 ) ,  o r  L r o m -p l e t e  ( C u m n r i n g  a n d  M o r r i s o n ,  1 9 6 0 ;  K l e i b e r ,  l 9 6 l ;  l l o r r i s o n ,  l 9 6 B )  f o o dd e p r i v a L i o n  o r ,  o n l y  i n  m a n ,  r a i s i n g  o f  i n t a k e  b y  o v e r f e e d i n g  ( l { i 1 l e rc n d  l ' 4 u m I o r d ,  1 9 6 7 \ ,  I n  t l r e s c  e x p e r i r n c n L s ,  c o n L r . l r y  t r r  t h o s e  i n  w h i e  he x p e n d i t u r e  w a s  m a n i p u l a r e d ,  b o d y  w e i g h t  d i d  n o t  r e m a i n  a !  t h e  e q u i l i -b r i u m  1 e v e 1  f o r  a d  l i b i t u m  c o n d i t i o n s .  A  n e w  b a l a n c e  b e t w e e n  i n t a k e  a n de x p e n d i t u r e  w a s  r e a c h e d  o n l y  s o m e t i m e s  ( K e y s  e t  a 1 . ,  \ r l a l k e r  a n dG . 3 r r e t t ,  l . c ,  ) .  T l r e s e  f e c L s  c o m p l  i c a L e  t h e  i n L . " r p r e t i r I i o n  o t  L l ) c  r e -s u l t s  w i E h  r e s p e c t  t o  t h e  q u e s t  i . r n  o [  r : . :  '  :  . '  .  . r t .  i ' :  , r .  , . :  -l ; , i , t t s .  S o m e  m e t a b o l i c  s a v i n q s  w i l l  r e s u l t  f r o n  t h e  m e r e  f a c t  t h a t  t h e*u n d e r I e d  s u b j e c t " ' h a s  t o  h a n d l e  a n d  d i q e s t  l e s s  f o , r d  ] l r r r € o v € r ,  d u r i n gn ; t r l  i a l  r r r  c o n r r r l p l e  l  - - : " ^ r :  -  ' !  -  t  o l r r c , r o a n  . r n d  l e T  , r r  p r / o n  n l r t <r \  L r  u i H r  r  r ( u r r s  5 ! \ \ v F (o f  t h e  c e l  l s  t h e m s e l v e s  a r e  u s e d  a s  f u e l .  B o d y  m a s s  w i l  I  d e c r e a s e ,  a n dr h i s  i s  b o u n d  t o  c 3 u s e  d  d r o p  i r L  m e L a b o l i s m .  H o w e v e r ,  I o L l o w i n g  C u m m i n ga n d  l l o r r i s o n  ( 1 . c . ) ,  T  w i L l  n o t  c e l l  r h e s e  d e . . r e a s e s  t a d e p t i v e t .R a t h e r .  I  a m  i n c l i n e d  t o  r e s t r i c t  t h i s  t e r n  t o  t h e  c a s e  w h e r e  L h e  u n -d e r I e d  a n i r n a l  s p e n d s  I c s s  f r e e  e n e r g y  o n . r  g i v e n  I u n c t i o n  ( e . g .  p r o L e i nE u r n o v e r ,  o r  m u s c u l a r  e f f o r t  f o r  a  g i v e n  b e h a v i o u r )  t h a n  a n  a d  l i b i c u mf  ed  conspec i f  i c  t -  L i t e  se t l v  r t t : t g i 1 |  and  body  , - , c rT i r t r s r l  l . i ' r r r  wou ld  do  (p .71 ) .I f  t h i s  p h e n o m e n o n  c o u l d  b e  s h o \ r n  t o  e x i s t ,  a  b a s i s  w o u l d  t h e r e b y  b el a i d  f o r  t h e  v i e w  t h a t  e v o l u t i o n  h a s  p r o v i d e d  t h e  i n d i v i d u a l  w i t h  a^ - ^  - :  ^ 1  ^ ^ . . ^ L :  r :  + "  r f  e k i  n s  o u t  i  t s  n r o v i s i o n s  i n  o r d e r  L o  i n c r e a s e  L h eL d P a u ,  r l L y  u r  l L J  t s l uc h a n c e  L h a t  i t  m a y  t i d e  o v e r  t e m p o r c r y  t o o d  s c e r c i r y ,  a  c o n d i t i o nx_." T h i s  d i s c u s s i o n  e m p h a s i s e s  t i r e  c a s e  o f  u n d e r f e e d i n g ,  s i n c e  t h i s  i s  t h eo n l y  c o n d i t i o n  u s e d  i n  m y  e x p e r i m e n t s .  A n  a n a l o g o u s  d e f i n i t i o n  o f ' a -d a p t a t i o n  o f  e x p e n d i t u r e  t o  u p t a k e '  c a n  b e  f o r m u l a t e d  f o r  t h e  c a s e  o fo v e r f e e d i n e .co f i non  i n  t he  na tu ra l hab i t a t  o f  many  spec ies .  Howeve r ,  such  a  de f i n i -t i o n  o f  a d a p t i v e  r e s ! r i c t i o n  o f  e x p e n d i t u r e  i n v o l v e s  f o r m i d a b l e  o p e r a -t i o n a l  d i f f i c u l t i e s .  I  s h a 1 l  r e E u r n  t o  s o m e  a s p e c t s  o f  t h i s  p r o b l e m s  i nc h a p t e r  8 .  F o r  t h e  m o m e n t  i t  w i l l  s u f f i c e  t o  s t a t e  t h a t  c o n c l u s i o n s  i nt he  t i ce ra tu re  a re  no t  unan imous  as  t o  r he  ques t i on  whe the r  o r  no tc h a n g e s  i n  m e t a b o l i s m  c a u s e d  b y  m a n i p u l a t i o n  o f  f o o d  i n L a k e ,  c a n  b ea c c o u n t e d  f o r  e x c l u s i v e l y  i n  t e r m s  o f  c h a n g e d  b o d y  m a s s  a n d  c e s s a t i o no f  f o o d  p r o c e s s i n g .  C u m m i n g  a n d  M o r r i s o n  ( 1 9 6 0 )  s t a t e :  ' T h e  t o t a l  e n e r -g y  e x p e n d i r u r e  o . [  L h e  r a t s  I e 1 I  d u r i n g  t h e  4 B  h r  f a s t  a n d  r o s e  d u r i n gre feed ing .  L t r en  t he  changes  i n  body  we ighc  and  f ood  i n t ake  we re  a l l owedfo r ,  t he  me tabo l i c  r a te  was  f ound  t o  r ema in  cons tan t  t h roughou t  t hew h o l e  e x p e r i r n e n t a l  p e r i o d t ,  I n  c o n t r a s t ,  W a l k e r  a n d  G a r r e t t  ( 1 - o 7 0 )c o n c l u d e  t h a t  e v e n  a f t e r  c o r r e c t i o n  f o r  b o d y  s i z e  r e d u c t i o n ' t h e  e n e r g yexpend i t u re  dec l i ned  marked l y  as  t he  pe r i od  o f  unde rnu t r i t i on  was  p ro -l o n g e d ' .  ( T h e y  d i d  n o t  t a k e  i n t o  a c c o u n t  c h a n g e d  c o s t s  o f  f o o d  p r o c e s -s i n g ,  b u t  E h i s  e f f e c c  w i l l  b e  c o r ) . s t a n t  f r o m  a b o u t  t h e  s e c o n d  d a y  o n -n a r d s ,  w h e r e a s  t h e  d e c r e a s e  c o n t i n u e d  b e y o n d  t h a t  t i m e , )T h e  p r e s e n t  s E u d y  i s  a  c o n t r i b u t i o n  t o  t h e  f u r t h e r  a n a l y s i s  o ft h e  p r o b l e r n  o f  a d a p t a t i o n  o f  e n e r g y  e x p e n d i t u r e  t o  u p E a k e .  C l e a r l y ,t h i s  c a n  n o t  b e  s o l v e d  b y  t h e  s t u d y  o f  t o t a l  m e t a b o l i c  r a l e  a l o n e ,  b u ton l y  by  an  ana l ys i s  o f  t he  va r i ous  componen ts  l ha t  make  up  t h i s  t o t a l .C u s t o m a r i l y  f o u r  c o m p o n e n t s  a r e  d i s t i n g u i s h e d  i n  t h e  e n e r g y  r n e t a b o l i s mo f  a  h o m e o t h e r m  ( G e s s a m a n ,  1 9 7 3 ) :  b a s a l  m e t a b o l i s m ;  m e t a b o l i s m  a b o v et h e  b a s a l  l e v e l  w h i c h  i s  u s e d  f o r  t h e r m o r e g u l a t i o n ;  m e t a b o l i s m  a s s o c i a -t e d  w i t h  a c t i v i t ' 1 ;  a n d  m e t a b o l i c  p r o c e s s e s  i n v o l v e d  i n  t h e  d i g e s t i o n  o ff o o d .  I  s h a l l  u s e  t h e  s a m e  d i v i s i o n .  H o w e v e r ,  i t  s h o u l d  b e  p o i n r e d  o u tt ha t  wha t  I  can  rneasu re  i n  my  expe r imen ts  i s  no t  t he  ra te  o f  ene rgye x p e n d i t u r e  e . g .  o n  t h e  p r o c e s s  o f  p e r f o r m i n g  m u s c u l a r  a c t i v i E y ,  b u ton l y  t he  d i f f e rence  i n  meuabo l i c  r a te  be tween  t he  pe r i od  du r i ng  wh i chtha t  ac t i v i t y  t akes  p l ace  and  pe r i ods  i n  wh i ch  t he  an ima l  i s  no t  en -g a g e d  i n  m u s c u l a r  a c E i v i t y .  T h i s  d i f f e r e n c e  g i v e s  r h e  c o s t  o f  a c r i v i r yon l y  i f  t he  o the r  componen ts  o f  ene rgy  expend i t u re  ( d i ges t i on  and  o the rp r o c e s s e s  i n  r e s L i n g  m u r a b o i i s m )  p r o c c e d  a t  r l r e  s J m e  r a L c  i r r e s p e c L i v eo f  t h e  o c c u r r e n c e  o f  r n u s c u l a r  a c t i v i t y .  T  h a v e  n o  m e a n s  o f  a s c e r t a i n i n gw h e t h e r  t h i s . i s  : ; o ,  b u t  i t  s e e m s  l r i g h l v  d o u h t f u l  f o r  i n s t a n c e  i n  v i e wn L  I h e  e f f e ,  t s  o I  s y m p a t h e r i . '  d i s c l r a r g e  a n d  e J r e n o m e d u l  l a r y  s e c r e t i o nc a u s i n g  s p l a n c h n i c  v a s c u l a r  c o n s t r i c t i o n ,  i n l r i b i t i o n  o f  l i p o g e n e s i s ,e t c .  I n  p r i n c i p l e  t h e r t f o r e  I  c e n  s t . r t e  o n l - v  t h e  d i f f e r e n c e  i n  m e t a b o -l i c  r : a t e  b e t w e e n  t h e  f  o L l o \ ^ / i n g  , ' . ) / r r 1 1 .  f . i : r t t s : .  l )  a n i m a l  r e s t i n g  i n  t h e  p o s t; r b s o r p t i v e  s L a t c ,  2 )  e n i m a l  r e s r i n g  r n d  p r o (  e s s i n g  f o o d .  3 )  a n i m a l  a c -t i v e .  F o r  b r e v i t y ,  h o w e v e r ,  I  s h a l l  d i s c u s s  m _ v  r e s u l t s  i n  t e r m s  o f  ar e s t i n g ,  a  f o o d  p r o c e s s i n g ,  s n d  - - L n  e c t i v i t y  , z o n r t ' t '  ) t ' +  c r f  m e t a b o l i s m  (( s e e  a l s o  p . 6 5 ) .  T h e  p o s s i b l e  i n f l u e n c e  o f  L h e  d e m a n d s  o f  t h e r m o r e g u l a -t i o n  o n  m e t a b o l i c  r a L c  c o u l d  b e  s t u d i e d  i n  p r i n c i p l . ' b y  m a k i n g  o b s e r -v a t i o n s  a f  d i f f e r e n t  a m b i e n t  t e m p e r i r t u r e s .  F o r  i n s t a n c e  i f  t h e  a n i m a li s  p l a c e d  i n  t h e  c o l d ,  t h i s  s h o u l d  l e a d  t o  a n  i n c r e a s e  i n  o n e  o r  m o r eo f  t h e  o L h e r  L l r r e e  c o m l ) o n e n t s  o f  m c t l b o l i s m .  S u e l r  r e m p e r d t u r e  c x p e r i -m e n L s ,  h o w e v e r ,  f e l l  o u t s i d e  t h e  s t ' o p e  o I  t h e  p r e s e n t  s t u d y .T h e  l a b o r a t o r y  r e t  w a s  c h o s e n  a s  t h e  s r r h . i e c t  o f  m v  e x p e r i m e n t s  b e -c a u s e  i t  i s  c o m m o n l y  u s e d  i n  s t u d i e s  o n  c a l t r r i c  r e g u l a c i o n .  I n t a k e  w a sc h a n p e d  i n  o n e  d i  r e c t  i , r n  n n l v  n A h p l v  r e d r r c f i o n -  A l  I  e r n c r i m e n t s  w e r eJ  t  r r s i ' r \d o n e  a t  t h e  s a m e  t e m p e r a t u r e  i n  t h e  t h e r m o n e u t r a l  z o n e  o f  f h e  r a t s  f o rE w o  r e a s o n s ,  F i r s E ,  I  w i s h e d  ! o  a v c i d  t h e  c o n r p l i c a t i o n  o f  s p e c i a l  ( a n dn o t  d i r e c t l y  m e a s u r a b l e )  h e a t  p r o d u c t i o n  f o r  t h e r m o r e g u l a t i o n .  S e c o n d ,e x p e r i m e n t s  w i t h  f o o d  d e p r i v e d  a n i m a l s  c a n  b o  c o n t i n u e d  l o n g e r  w i  t h o u tl p f h a l  p f I p c t s -  f o r  a L  t e m n e r a t u r ( , s  i n  o r  n e a r  l l r e  L h e r m r . n e u t r a l  z o D ea n i m a l s  c a n  r n o b i l i z e  m o r e  o f  t h e i r  e n e r g y  s t u r e s  a s  s h o w n  b y  d a t a  o nb i r d s  ( K e n d e i g h ,  1 9 4 5 )  a n d  r a t s  ( K l e i b e r ,  1 9 4 5 )  s t a r v e d  t i l l  d e a c h  a td i f f e r e n t  t e m p e r a t u r e s ,  C o n s e q u e n t l y  i n  m y  e x p e r i m e n t s ,  n o t w i t h s t a n d -i n g  l o n g  p e r i o d s  o f  f o o d  d e p r i v a t i o n ,  o n l v  t w o  o u t  o f  m o r e  t h a n  o n eh u n d r e d  a n i m a l s  d i e d :  t h e  o t h e r : s  c o u l d  b e  r e f e d .T h e  e n e r g y  e x p e n d i t u r e  w a s  m c a s u r e d  b y  t w  m e t h o d s :  l )  a  b a l a n c et e c h n i q u e  ( c h a p t e r  3 ) ,  c a l c u l a t i n g  e x p e n d i t u r e  f r o m  f o o d  i n t a k e ,  f a e c e sp r o d u c t i o n  a n d  c h a n g e s  i n  b o d y  r e s e r v e s ,  a n d  2 )  i n d i r e c L  c a l o r i m e t r y ,c a l c u l a t i n g  e x p e n d i t u r e  f r o m  t h e  g a s  e x c h a n g c  o f  t h c  a n i m a l s  ( c h a p r e r st4 -7 ) .  By  i nc reas ing  t he  t empo ra l  r eso lu t i on  o f  t he  l a t t e r  me thod  andcomb in i ng  i t  w i t h  o the r  r echn iques  a  de ta i l ed  ana l ys i s  o f  t oLa l  expen -d i t u r e  i n t o  i t s  c o m p o n e n t s  w a s  m a d e  p o s s i b l e ,  T h i s  p r o c e c i u r e  w i l l  b ed e s c r i b e d  i n  d e L a i l  i n  c h a p t e r  2 .I  f i r s t  de te rm ined  t he  change  i n  t o t . a r  expend i t u re  du r i ng  f ooddep r i va t i on  ( chap re r  3 ) ,  Th i s  change  \ ^ / as  f u r t he r  ana l ysed  i n  t e rms  o ft h e  e n e r g e t i c  c o n s e q u e n c e s  o f :  l )  t h e  c e s s a E i o n  o f  f o o d  p r o c e s s i n g( c h a p t e r  4 ) ; 2 )  c h a n g e s  o f  a c r i v i r y  ( c h a p t e r  5 ) ;  a n d  3 )  c h a n g e s  o ff a s t i n g  r e s t i n g  m e t a b o l i c  r a t e  ( c h a p t e r  5 ) .  F i n a l l y  t h e  c o n s e q u e n c e so f  t he  expend i t u re  changes  f o r  r egu la t i on  o f  body  t empe ra tu re  we res t u d i e d  ( c h a p t e r  7 ) .  w i t h  r e s p e c t  t o  t h e  f i r s t  p o i n r  i u  i s  r e g r e t t a b l etha t  t he  ene rgy  expend i t u re  on  f eed ing  behav iou r  cou ld  no t  be  sepa ra -red  f r om Lha t  on  o the r  behav iou r .  The re fo re  my  es t ima te  o f  t he  ene rgye x p e n d i t u r e  a s s o c i a r e d  w i t h  f o o d  p r o c e s s i n g  i n c l u d e d  o n l y  t h e  c o s t s  o fi n t e rna l  p r : ocess ing ,  wh i l e  f o r  i ns tance  f ood  hand l i ng  was  measu red  t o -ge the r  w i t h  t he  cos t s  o f  non - f eed ing  behav iou r .

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   University of GroningenHow rats economizeWesterterp, Klaas RoelofIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:1976Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Westerterp, K. R. (1976). How rats economize: Energy loss in starvation. s.n.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 09-09-2023CHAPTER IGENERAL INTRODUCTIONA d u l t  a n i r n a l s ,  l i v i n g  i n  a  c o n s t a n t  b i o l o g i c a l l y  a d e q u a t e  e n v i r o n m e n t ,ma in ta i n  a  ba lance  be tween  ene rgy  up take  and  ene rgv  expend i t u re .  Thee n e r g y  s t o r e  o f  t h e  b o d y  d o e s  n o t  f l u c t u a t e  m u c h ,  a s  t h e  c o n s t a n c y  o fbody  we igh t  and  body  compos i t i on  s t r ows ,  wh i l e  t he  s to re  i s  sma l l  i nc o m p a r i s o n  t o  t h e  d a i l y  e n e r g y  t u r n o v e r ,  e s p e c i a l l y  i n  s m a l l  a n i m a l s .T h i s  c a n  b e a c l . i e v e ' J  e i t h e r  b y  c o n t r o l  o f  t h e  u p t a k e  o r  t h e  e x p e n d i t u r eo f  e n e r g y .Tha t  an  an ima l  adap t s  i t s  up rake  t o  t he  expend i t u re  o f  ene rgy  i swe i l  known .  S tud ies  on  t h i s  po in t  we re  done  by  man ipu la t i ng  ene rgy  ex -pend i t u re  v i a  a  change  o f  env i r onmen ta l  t empe ra tu re  o r  v i a  t he  amoun to f  a c t i v i t y  i m p o s e d  o n  t h e  a n i m a l .  C o r t l e  a n d  C a r l s o n  ( 1 9 5 4 )  i n c r e a s e dt h e  e n e r g y  e x p e n d i t u r e  i n  r a E s  b y  l o w e r i n g  E h e  e n v i r o n m e n t a l  t e m p e r a -t u re  f r om 25o  C ,  a  va l ue  i n  o r  c l ose  t o  t he  t he rmoneuL ra l  zone  o f  t hese. - o ^an ima l s ,  t o  5 "  C .  An ima l s  p l aced  i n  t h i s  co l d  env i r onmen !  a te  tw i ce  asmuch  as  t he i r  con t ro l s  i n  t he  wa rm env i r onmen t .  Maye r  e t  a l .  ( 1954 )  ex -e r c i s e d  r a t s  i n  a  t r e a d m i l l  w i t h  a  s p e e d  o f  o n e  m i l e  p e r  h o u r .  T h e  a n i -ma l s  p rac t i ca l l y  doub led  t he i r  f ood  i n t ake  when  t he  du ra t i on  o f  exe r -c i se  was  i nc reased  f r om one  t o  s i x  hou rs  pe r  day ,  wh i l e  bod . v  we igh t  wasma in ta i ned .  The  measu red  changes  o f  f ood  i n t ake  we re  rep resen ta t i ve  f o re n c r g y  r . r p t a k e  b e c a u s e  i n  a d u l t  r a t s  i m p o r t a n t  c h a n g e s  o f  d i g e s r i o n  e f -f i c i ency  i n  r e l a t i on  t o  l he  l eve l  o f  f ood  i n t ake  a re  neve r  f ound( N e h r i n g  e t  a l . ,  1 9 5 9 ) .  I n  b o t h  e x p e r i m e n E s  m e n t i o n e d  a  b a l a n c e  b e t w e e nup take  and  expend i t u re  was  reached  aga in  unde r  t he  new  c i r cums tances  asshown  by  t he  cons tancy  o f  body  we igh t  du r i ng  more  t han  one  week .  Mo re -ove r ,  t he  s i ze  o f  t he  rese rves  was  p robab l y  no t  i - n f l uenced  because  t h i sbody  we igh t  had  t he  no rma l  va l ue .To  conc lude ,  an  an ima l  can  change  i t s  ene rgy  up t . ake  w i t h  a t  l eas ta  f ac to r  two  f o r  adap t i ng  i t  t o  t he  expend i t u re  o f  ene rgy .T h e  p o s s i b i L i t i r  t h a t  i t n  a n i m a l  a d a p t s  i t s  e x p e n d i c u r e  t o  t h e  u p -t a k e  o [  e n e r g y  i s  o f t e n  c a l l e d  i n  q u e s t i o n .  R e c e n L l y  L e  ] 4 a g n e n  ( 1 9 7 4 )c v c n  s L A L ( ' d  t l ) a t  L I ) e  (  L \ t ) t r r r l  d f  c n c r q y  o x p e n d i t u r e  i s  c ( , n L r ; r r y  t o  w h a Lb o d y  v i e i g h t  w o u l c i  r e q u i r e  i n  v i e w  o f  h y p e r a c t i v i t y  i n  f o o d  d e p r i v a t i o na n d  h y p o a c t i v i t y  i n  o b e s i t y .  l n v e s t i g a t i o n s  o n  t h i s  p o i n L  a v a i l a b L e  i nt h e  l i t e r a t u r e  i n v o l v e d  e i t h e r  p a r t i a l  ( K e y s  e t  a L . ,  1 9 5 0 ;  G r a n d e  e ti r 1 . ,  l 9 5 B ;  M e y e r  a n d  C l a w s o n ,  1 9 6 4 ;  l " l a l k t ' r  a n d  t l a r r e t t ,  I 9 7 0 ) ,  o r  L r o m -p l e t e  ( C u m n r i n g  a n d  M o r r i s o n ,  1 9 6 0 ;  K l e i b e r ,  l 9 6 l ;  l l o r r i s o n ,  l 9 6 B )  f o o dd e p r i v a L i o n  o r ,  o n l y  i n  m a n ,  r a i s i n g  o f  i n t a k e  b y  o v e r f e e d i n g  ( l { i 1 l e rc n d  l ' 4 u m I o r d ,  1 9 6 7 \ ,  I n  t l r e s c  e x p e r i r n c n L s ,  c o n L r . l r y  t r r  t h o s e  i n  w h i e  he x p e n d i t u r e  w a s  m a n i p u l a r e d ,  b o d y  w e i g h t  d i d  n o t  r e m a i n  a !  t h e  e q u i l i -b r i u m  1 e v e 1  f o r  a d  l i b i t u m  c o n d i t i o n s .  A  n e w  b a l a n c e  b e t w e e n  i n t a k e  a n de x p e n d i t u r e  w a s  r e a c h e d  o n l y  s o m e t i m e s  ( K e y s  e t  a 1 . ,  \ r l a l k e r  a n dG . 3 r r e t t ,  l . c ,  ) .  T l r e s e  f e c L s  c o m p l  i c a L e  t h e  i n L . " r p r e t i r I i o n  o t  L l ) c  r e -s u l t s  w i E h  r e s p e c t  t o  t h e  q u e s t  i . r n  o [  r : . :  '  :  . '  .  . r t .  i ' :  , r .  , . :  -l ; , i , t t s .  S o m e  m e t a b o l i c  s a v i n q s  w i l l  r e s u l t  f r o n  t h e  m e r e  f a c t  t h a t  t h e*u n d e r I e d  s u b j e c t " ' h a s  t o  h a n d l e  a n d  d i q e s t  l e s s  f o , r d  ] l r r r € o v € r ,  d u r i n gn ; t r l  i a l  r r r  c o n r r r l p l e  l  - - : " ^ r :  -  ' !  -  t  o l r r c , r o a n  . r n d  l e T  , r r  p r / o n  n l r t <r \  L r  u i H r  r  r ( u r r s  5 ! \ \ v F (o f  t h e  c e l  l s  t h e m s e l v e s  a r e  u s e d  a s  f u e l .  B o d y  m a s s  w i l  I  d e c r e a s e ,  a n dr h i s  i s  b o u n d  t o  c 3 u s e  d  d r o p  i r L  m e L a b o l i s m .  H o w e v e r ,  I o L l o w i n g  C u m m i n ga n d  l l o r r i s o n  ( 1 . c . ) ,  T  w i L l  n o t  c e l l  r h e s e  d e . . r e a s e s  t a d e p t i v e t .R a t h e r .  I  a m  i n c l i n e d  t o  r e s t r i c t  t h i s  t e r n  t o  t h e  c a s e  w h e r e  L h e  u n -d e r I e d  a n i r n a l  s p e n d s  I c s s  f r e e  e n e r g y  o n . r  g i v e n  I u n c t i o n  ( e . g .  p r o L e i nE u r n o v e r ,  o r  m u s c u l a r  e f f o r t  f o r  a  g i v e n  b e h a v i o u r )  t h a n  a n  a d  l i b i c u mf  ed  conspec i f  i c  t -  L i t e  se t l v  r t t : t g i 1 |  and  body  , - , c rT i r t r s r l  l . i ' r r r  wou ld  do  (p .71 ) .I f  t h i s  p h e n o m e n o n  c o u l d  b e  s h o \ r n  t o  e x i s t ,  a  b a s i s  w o u l d  t h e r e b y  b el a i d  f o r  t h e  v i e w  t h a t  e v o l u t i o n  h a s  p r o v i d e d  t h e  i n d i v i d u a l  w i t h  a^ - ^  - :  ^ 1  ^ ^ . . ^ L :  r :  + "  r f  e k i  n s  o u t  i  t s  n r o v i s i o n s  i n  o r d e r  L o  i n c r e a s e  L h eL d P a u ,  r l L y  u r  l L J  t s l uc h a n c e  L h a t  i t  m a y  t i d e  o v e r  t e m p o r c r y  t o o d  s c e r c i r y ,  a  c o n d i t i o nx_." T h i s  d i s c u s s i o n  e m p h a s i s e s  t i r e  c a s e  o f  u n d e r f e e d i n g ,  s i n c e  t h i s  i s  t h eo n l y  c o n d i t i o n  u s e d  i n  m y  e x p e r i m e n t s .  A n  a n a l o g o u s  d e f i n i t i o n  o f ' a -d a p t a t i o n  o f  e x p e n d i t u r e  t o  u p t a k e '  c a n  b e  f o r m u l a t e d  f o r  t h e  c a s e  o fo v e r f e e d i n e .co f i non  i n  t he  na tu ra l hab i t a t  o f  many  spec ies .  Howeve r ,  such  a  de f i n i -t i o n  o f  a d a p t i v e  r e s ! r i c t i o n  o f  e x p e n d i t u r e  i n v o l v e s  f o r m i d a b l e  o p e r a -t i o n a l  d i f f i c u l t i e s .  I  s h a 1 l  r e E u r n  t o  s o m e  a s p e c t s  o f  t h i s  p r o b l e m s  i nc h a p t e r  8 .  F o r  t h e  m o m e n t  i t  w i l l  s u f f i c e  t o  s t a t e  t h a t  c o n c l u s i o n s  i nt he  t i ce ra tu re  a re  no t  unan imous  as  t o  r he  ques t i on  whe the r  o r  no tc h a n g e s  i n  m e t a b o l i s m  c a u s e d  b y  m a n i p u l a t i o n  o f  f o o d  i n L a k e ,  c a n  b ea c c o u n t e d  f o r  e x c l u s i v e l y  i n  t e r m s  o f  c h a n g e d  b o d y  m a s s  a n d  c e s s a t i o no f  f o o d  p r o c e s s i n g .  C u m m i n g  a n d  M o r r i s o n  ( 1 9 6 0 )  s t a t e :  ' T h e  t o t a l  e n e r -g y  e x p e n d i r u r e  o . [  L h e  r a t s  I e 1 I  d u r i n g  t h e  4 B  h r  f a s t  a n d  r o s e  d u r i n gre feed ing .  L t r en  t he  changes  i n  body  we ighc  and  f ood  i n t ake  we re  a l l owedfo r ,  t he  me tabo l i c  r a te  was  f ound  t o  r ema in  cons tan t  t h roughou t  t hew h o l e  e x p e r i r n e n t a l  p e r i o d t ,  I n  c o n t r a s t ,  W a l k e r  a n d  G a r r e t t  ( 1 - o 7 0 )c o n c l u d e  t h a t  e v e n  a f t e r  c o r r e c t i o n  f o r  b o d y  s i z e  r e d u c t i o n ' t h e  e n e r g yexpend i t u re  dec l i ned  marked l y  as  t he  pe r i od  o f  unde rnu t r i t i on  was  p ro -l o n g e d ' .  ( T h e y  d i d  n o t  t a k e  i n t o  a c c o u n t  c h a n g e d  c o s t s  o f  f o o d  p r o c e s -s i n g ,  b u t  E h i s  e f f e c c  w i l l  b e  c o r ) . s t a n t  f r o m  a b o u t  t h e  s e c o n d  d a y  o n -n a r d s ,  w h e r e a s  t h e  d e c r e a s e  c o n t i n u e d  b e y o n d  t h a t  t i m e , )T h e  p r e s e n t  s E u d y  i s  a  c o n t r i b u t i o n  t o  t h e  f u r t h e r  a n a l y s i s  o ft h e  p r o b l e r n  o f  a d a p t a t i o n  o f  e n e r g y  e x p e n d i t u r e  t o  u p E a k e .  C l e a r l y ,t h i s  c a n  n o t  b e  s o l v e d  b y  t h e  s t u d y  o f  t o t a l  m e t a b o l i c  r a l e  a l o n e ,  b u ton l y  by  an  ana l ys i s  o f  t he  va r i ous  componen ts  l ha t  make  up  t h i s  t o t a l .C u s t o m a r i l y  f o u r  c o m p o n e n t s  a r e  d i s t i n g u i s h e d  i n  t h e  e n e r g y  r n e t a b o l i s mo f  a  h o m e o t h e r m  ( G e s s a m a n ,  1 9 7 3 ) :  b a s a l  m e t a b o l i s m ;  m e t a b o l i s m  a b o v et h e  b a s a l  l e v e l  w h i c h  i s  u s e d  f o r  t h e r m o r e g u l a t i o n ;  m e t a b o l i s m  a s s o c i a -t e d  w i t h  a c t i v i t ' 1 ;  a n d  m e t a b o l i c  p r o c e s s e s  i n v o l v e d  i n  t h e  d i g e s t i o n  o ff o o d .  I  s h a l l  u s e  t h e  s a m e  d i v i s i o n .  H o w e v e r ,  i t  s h o u l d  b e  p o i n r e d  o u tt ha t  wha t  I  can  rneasu re  i n  my  expe r imen ts  i s  no t  t he  ra te  o f  ene rgye x p e n d i t u r e  e . g .  o n  t h e  p r o c e s s  o f  p e r f o r m i n g  m u s c u l a r  a c t i v i E y ,  b u ton l y  t he  d i f f e rence  i n  meuabo l i c  r a te  be tween  t he  pe r i od  du r i ng  wh i chtha t  ac t i v i t y  t akes  p l ace  and  pe r i ods  i n  wh i ch  t he  an ima l  i s  no t  en -g a g e d  i n  m u s c u l a r  a c E i v i t y .  T h i s  d i f f e r e n c e  g i v e s  r h e  c o s t  o f  a c r i v i r yon l y  i f  t he  o the r  componen ts  o f  ene rgy  expend i t u re  ( d i ges t i on  and  o the rp r o c e s s e s  i n  r e s L i n g  m u r a b o i i s m )  p r o c c e d  a t  r l r e  s J m e  r a L c  i r r e s p e c L i v eo f  t h e  o c c u r r e n c e  o f  r n u s c u l a r  a c t i v i t y .  T  h a v e  n o  m e a n s  o f  a s c e r t a i n i n gw h e t h e r  t h i s . i s  : ; o ,  b u t  i t  s e e m s  l r i g h l v  d o u h t f u l  f o r  i n s t a n c e  i n  v i e wn L  I h e  e f f e ,  t s  o I  s y m p a t h e r i . '  d i s c l r a r g e  a n d  e J r e n o m e d u l  l a r y  s e c r e t i o nc a u s i n g  s p l a n c h n i c  v a s c u l a r  c o n s t r i c t i o n ,  i n l r i b i t i o n  o f  l i p o g e n e s i s ,e t c .  I n  p r i n c i p l e  t h e r t f o r e  I  c e n  s t . r t e  o n l - v  t h e  d i f f e r e n c e  i n  m e t a b o -l i c  r : a t e  b e t w e e n  t h e  f  o L l o \ ^ / i n g  , ' . ) / r r 1 1 .  f . i : r t t s : .  l )  a n i m a l  r e s t i n g  i n  t h e  p o s t; r b s o r p t i v e  s L a t c ,  2 )  e n i m a l  r e s r i n g  r n d  p r o (  e s s i n g  f o o d .  3 )  a n i m a l  a c -t i v e .  F o r  b r e v i t y ,  h o w e v e r ,  I  s h a l l  d i s c u s s  m _ v  r e s u l t s  i n  t e r m s  o f  ar e s t i n g ,  a  f o o d  p r o c e s s i n g ,  s n d  - - L n  e c t i v i t y  , z o n r t ' t '  ) t ' +  c r f  m e t a b o l i s m  (( s e e  a l s o  p . 6 5 ) .  T h e  p o s s i b l e  i n f l u e n c e  o f  L h e  d e m a n d s  o f  t h e r m o r e g u l a -t i o n  o n  m e t a b o l i c  r a L c  c o u l d  b e  s t u d i e d  i n  p r i n c i p l . ' b y  m a k i n g  o b s e r -v a t i o n s  a f  d i f f e r e n t  a m b i e n t  t e m p e r i r t u r e s .  F o r  i n s t a n c e  i f  t h e  a n i m a li s  p l a c e d  i n  t h e  c o l d ,  t h i s  s h o u l d  l e a d  t o  a n  i n c r e a s e  i n  o n e  o r  m o r eo f  t h e  o L h e r  L l r r e e  c o m l ) o n e n t s  o f  m c t l b o l i s m .  S u e l r  r e m p e r d t u r e  c x p e r i -m e n L s ,  h o w e v e r ,  f e l l  o u t s i d e  t h e  s t ' o p e  o I  t h e  p r e s e n t  s t u d y .T h e  l a b o r a t o r y  r e t  w a s  c h o s e n  a s  t h e  s r r h . i e c t  o f  m v  e x p e r i m e n t s  b e -c a u s e  i t  i s  c o m m o n l y  u s e d  i n  s t u d i e s  o n  c a l t r r i c  r e g u l a c i o n .  I n t a k e  w a sc h a n p e d  i n  o n e  d i  r e c t  i , r n  n n l v  n A h p l v  r e d r r c f i o n -  A l  I  e r n c r i m e n t s  w e r eJ  t  r r s i ' r \d o n e  a t  t h e  s a m e  t e m p e r a t u r e  i n  t h e  t h e r m o n e u t r a l  z o n e  o f  f h e  r a t s  f o rE w o  r e a s o n s ,  F i r s E ,  I  w i s h e d  ! o  a v c i d  t h e  c o n r p l i c a t i o n  o f  s p e c i a l  ( a n dn o t  d i r e c t l y  m e a s u r a b l e )  h e a t  p r o d u c t i o n  f o r  t h e r m o r e g u l a t i o n .  S e c o n d ,e x p e r i m e n t s  w i t h  f o o d  d e p r i v e d  a n i m a l s  c a n  b o  c o n t i n u e d  l o n g e r  w i  t h o u tl p f h a l  p f I p c t s -  f o r  a L  t e m n e r a t u r ( , s  i n  o r  n e a r  l l r e  L h e r m r . n e u t r a l  z o D ea n i m a l s  c a n  r n o b i l i z e  m o r e  o f  t h e i r  e n e r g y  s t u r e s  a s  s h o w n  b y  d a t a  o nb i r d s  ( K e n d e i g h ,  1 9 4 5 )  a n d  r a t s  ( K l e i b e r ,  1 9 4 5 )  s t a r v e d  t i l l  d e a c h  a td i f f e r e n t  t e m p e r a t u r e s ,  C o n s e q u e n t l y  i n  m y  e x p e r i m e n t s ,  n o t w i t h s t a n d -i n g  l o n g  p e r i o d s  o f  f o o d  d e p r i v a t i o n ,  o n l v  t w o  o u t  o f  m o r e  t h a n  o n eh u n d r e d  a n i m a l s  d i e d :  t h e  o t h e r : s  c o u l d  b e  r e f e d .T h e  e n e r g y  e x p e n d i t u r e  w a s  m c a s u r e d  b y  t w  m e t h o d s :  l )  a  b a l a n c et e c h n i q u e  ( c h a p t e r  3 ) ,  c a l c u l a t i n g  e x p e n d i t u r e  f r o m  f o o d  i n t a k e ,  f a e c e sp r o d u c t i o n  a n d  c h a n g e s  i n  b o d y  r e s e r v e s ,  a n d  2 )  i n d i r e c L  c a l o r i m e t r y ,c a l c u l a t i n g  e x p e n d i t u r e  f r o m  t h e  g a s  e x c h a n g c  o f  t h c  a n i m a l s  ( c h a p r e r st4 -7 ) .  By  i nc reas ing  t he  t empo ra l  r eso lu t i on  o f  t he  l a t t e r  me thod  andcomb in i ng  i t  w i t h  o the r  r echn iques  a  de ta i l ed  ana l ys i s  o f  t oLa l  expen -d i t u r e  i n t o  i t s  c o m p o n e n t s  w a s  m a d e  p o s s i b l e ,  T h i s  p r o c e c i u r e  w i l l  b ed e s c r i b e d  i n  d e L a i l  i n  c h a p t e r  2 .I  f i r s t  de te rm ined  t he  change  i n  t o t . a r  expend i t u re  du r i ng  f ooddep r i va t i on  ( chap re r  3 ) ,  Th i s  change  \ ^ / as  f u r t he r  ana l ysed  i n  t e rms  o ft h e  e n e r g e t i c  c o n s e q u e n c e s  o f :  l )  t h e  c e s s a E i o n  o f  f o o d  p r o c e s s i n g( c h a p t e r  4 ) ; 2 )  c h a n g e s  o f  a c r i v i r y  ( c h a p t e r  5 ) ;  a n d  3 )  c h a n g e s  o ff a s t i n g  r e s t i n g  m e t a b o l i c  r a t e  ( c h a p t e r  5 ) .  F i n a l l y  t h e  c o n s e q u e n c e so f  t he  expend i t u re  changes  f o r  r egu la t i on  o f  body  t empe ra tu re  we res t u d i e d  ( c h a p t e r  7 ) .  w i t h  r e s p e c t  t o  t h e  f i r s t  p o i n r  i u  i s  r e g r e t t a b l etha t  t he  ene rgy  expend i t u re  on  f eed ing  behav iou r  cou ld  no t  be  sepa ra -red  f r om Lha t  on  o the r  behav iou r .  The re fo re  my  es t ima te  o f  t he  ene rgye x p e n d i t u r e  a s s o c i a r e d  w i t h  f o o d  p r o c e s s i n g  i n c l u d e d  o n l y  t h e  c o s t s  o fi n t e rna l  p r : ocess ing ,  wh i l e  f o r  i ns tance  f ood  hand l i ng  was  measu red  t o -ge the r  w i t h  t he  cos t s  o f  non - f eed ing  behav iou r .

NARCIS 

How rats economize: Energy loss in starvation

Proceedings - University of Groningen

   University of GroningenHow rats economizeWesterterp, Klaas RoelofIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:1976Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Westerterp, K. R. (1976). How rats economize: Energy loss in starvation. s.n.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 03-06-2022CHAPTER IGENERAL INTRODUCTIONA d u l t  a n i r n a l s ,  l i v i n g  i n  a  c o n s t a n t  b i o l o g i c a l l y  a d e q u a t e  e n v i r o n m e n t ,ma in ta i n  a  ba lance  be tween  ene rgy  up take  and  ene rgv  expend i t u re .  Thee n e r g y  s t o r e  o f  t h e  b o d y  d o e s  n o t  f l u c t u a t e  m u c h ,  a s  t h e  c o n s t a n c y  o fbody  we igh t  and  body  compos i t i on  s t r ows ,  wh i l e  t he  s to re  i s  sma l l  i nc o m p a r i s o n  t o  t h e  d a i l y  e n e r g y  t u r n o v e r ,  e s p e c i a l l y  i n  s m a l l  a n i m a l s .T h i s  c a n  b e a c l . i e v e ' J  e i t h e r  b y  c o n t r o l  o f  t h e  u p t a k e  o r  t h e  e x p e n d i t u r eo f  e n e r g y .Tha t  an  an ima l  adap t s  i t s  up rake  t o  t he  expend i t u re  o f  ene rgy  i swe i l  known .  S tud ies  on  t h i s  po in t  we re  done  by  man ipu la t i ng  ene rgy  ex -pend i t u re  v i a  a  change  o f  env i r onmen ta l  t empe ra tu re  o r  v i a  t he  amoun to f  a c t i v i t y  i m p o s e d  o n  t h e  a n i m a l .  C o r t l e  a n d  C a r l s o n  ( 1 9 5 4 )  i n c r e a s e dt h e  e n e r g y  e x p e n d i t u r e  i n  r a E s  b y  l o w e r i n g  E h e  e n v i r o n m e n t a l  t e m p e r a -t u re  f r om 25o  C ,  a  va l ue  i n  o r  c l ose  t o  t he  t he rmoneuL ra l  zone  o f  t hese. - o ^an ima l s ,  t o  5 "  C .  An ima l s  p l aced  i n  t h i s  co l d  env i r onmen !  a te  tw i ce  asmuch  as  t he i r  con t ro l s  i n  t he  wa rm env i r onmen t .  Maye r  e t  a l .  ( 1954 )  ex -e r c i s e d  r a t s  i n  a  t r e a d m i l l  w i t h  a  s p e e d  o f  o n e  m i l e  p e r  h o u r .  T h e  a n i -ma l s  p rac t i ca l l y  doub led  t he i r  f ood  i n t ake  when  t he  du ra t i on  o f  exe r -c i se  was  i nc reased  f r om one  t o  s i x  hou rs  pe r  day ,  wh i l e  bod . v  we igh t  wasma in ta i ned .  The  measu red  changes  o f  f ood  i n t ake  we re  rep resen ta t i ve  f o re n c r g y  r . r p t a k e  b e c a u s e  i n  a d u l t  r a t s  i m p o r t a n t  c h a n g e s  o f  d i g e s r i o n  e f -f i c i ency  i n  r e l a t i on  t o  l he  l eve l  o f  f ood  i n t ake  a re  neve r  f ound( N e h r i n g  e t  a l . ,  1 9 5 9 ) .  I n  b o t h  e x p e r i m e n E s  m e n t i o n e d  a  b a l a n c e  b e t w e e nup take  and  expend i t u re  was  reached  aga in  unde r  t he  new  c i r cums tances  asshown  by  t he  cons tancy  o f  body  we igh t  du r i ng  more  t han  one  week .  Mo re -ove r ,  t he  s i ze  o f  t he  rese rves  was  p robab l y  no t  i - n f l uenced  because  t h i sbody  we igh t  had  t he  no rma l  va l ue .To  conc lude ,  an  an ima l  can  change  i t s  ene rgy  up t . ake  w i t h  a t  l eas ta  f ac to r  two  f o r  adap t i ng  i t  t o  t he  expend i t u re  o f  ene rgy .T h e  p o s s i b i L i t i r  t h a t  i t n  a n i m a l  a d a p t s  i t s  e x p e n d i c u r e  t o  t h e  u p -t a k e  o [  e n e r g y  i s  o f t e n  c a l l e d  i n  q u e s t i o n .  R e c e n L l y  L e  ] 4 a g n e n  ( 1 9 7 4 )c v c n  s L A L ( ' d  t l ) a t  L I ) e  (  L \ t ) t r r r l  d f  c n c r q y  o x p e n d i t u r e  i s  c ( , n L r ; r r y  t o  w h a Lb o d y  v i e i g h t  w o u l c i  r e q u i r e  i n  v i e w  o f  h y p e r a c t i v i t y  i n  f o o d  d e p r i v a t i o na n d  h y p o a c t i v i t y  i n  o b e s i t y .  l n v e s t i g a t i o n s  o n  t h i s  p o i n L  a v a i l a b L e  i nt h e  l i t e r a t u r e  i n v o l v e d  e i t h e r  p a r t i a l  ( K e y s  e t  a L . ,  1 9 5 0 ;  G r a n d e  e ti r 1 . ,  l 9 5 B ;  M e y e r  a n d  C l a w s o n ,  1 9 6 4 ;  l " l a l k t ' r  a n d  t l a r r e t t ,  I 9 7 0 ) ,  o r  L r o m -p l e t e  ( C u m n r i n g  a n d  M o r r i s o n ,  1 9 6 0 ;  K l e i b e r ,  l 9 6 l ;  l l o r r i s o n ,  l 9 6 B )  f o o dd e p r i v a L i o n  o r ,  o n l y  i n  m a n ,  r a i s i n g  o f  i n t a k e  b y  o v e r f e e d i n g  ( l { i 1 l e rc n d  l ' 4 u m I o r d ,  1 9 6 7 \ ,  I n  t l r e s c  e x p e r i r n c n L s ,  c o n L r . l r y  t r r  t h o s e  i n  w h i e  he x p e n d i t u r e  w a s  m a n i p u l a r e d ,  b o d y  w e i g h t  d i d  n o t  r e m a i n  a !  t h e  e q u i l i -b r i u m  1 e v e 1  f o r  a d  l i b i t u m  c o n d i t i o n s .  A  n e w  b a l a n c e  b e t w e e n  i n t a k e  a n de x p e n d i t u r e  w a s  r e a c h e d  o n l y  s o m e t i m e s  ( K e y s  e t  a 1 . ,  \ r l a l k e r  a n dG . 3 r r e t t ,  l . c ,  ) .  T l r e s e  f e c L s  c o m p l  i c a L e  t h e  i n L . " r p r e t i r I i o n  o t  L l ) c  r e -s u l t s  w i E h  r e s p e c t  t o  t h e  q u e s t  i . r n  o [  r : . :  '  :  . '  .  . r t .  i ' :  , r .  , . :  -l ; , i , t t s .  S o m e  m e t a b o l i c  s a v i n q s  w i l l  r e s u l t  f r o n  t h e  m e r e  f a c t  t h a t  t h e*u n d e r I e d  s u b j e c t " ' h a s  t o  h a n d l e  a n d  d i q e s t  l e s s  f o , r d  ] l r r r € o v € r ,  d u r i n gn ; t r l  i a l  r r r  c o n r r r l p l e  l  - - : " ^ r :  -  ' !  -  t  o l r r c , r o a n  . r n d  l e T  , r r  p r / o n  n l r t <r \  L r  u i H r  r  r ( u r r s  5 ! \ \ v F (o f  t h e  c e l  l s  t h e m s e l v e s  a r e  u s e d  a s  f u e l .  B o d y  m a s s  w i l  I  d e c r e a s e ,  a n dr h i s  i s  b o u n d  t o  c 3 u s e  d  d r o p  i r L  m e L a b o l i s m .  H o w e v e r ,  I o L l o w i n g  C u m m i n ga n d  l l o r r i s o n  ( 1 . c . ) ,  T  w i L l  n o t  c e l l  r h e s e  d e . . r e a s e s  t a d e p t i v e t .R a t h e r .  I  a m  i n c l i n e d  t o  r e s t r i c t  t h i s  t e r n  t o  t h e  c a s e  w h e r e  L h e  u n -d e r I e d  a n i r n a l  s p e n d s  I c s s  f r e e  e n e r g y  o n . r  g i v e n  I u n c t i o n  ( e . g .  p r o L e i nE u r n o v e r ,  o r  m u s c u l a r  e f f o r t  f o r  a  g i v e n  b e h a v i o u r )  t h a n  a n  a d  l i b i c u mf  ed  conspec i f  i c  t -  L i t e  se t l v  r t t : t g i 1 |  and  body  , - , c rT i r t r s r l  l . i ' r r r  wou ld  do  (p .71 ) .I f  t h i s  p h e n o m e n o n  c o u l d  b e  s h o \ r n  t o  e x i s t ,  a  b a s i s  w o u l d  t h e r e b y  b el a i d  f o r  t h e  v i e w  t h a t  e v o l u t i o n  h a s  p r o v i d e d  t h e  i n d i v i d u a l  w i t h  a^ - ^  - :  ^ 1  ^ ^ . . ^ L :  r :  + "  r f  e k i  n s  o u t  i  t s  n r o v i s i o n s  i n  o r d e r  L o  i n c r e a s e  L h eL d P a u ,  r l L y  u r  l L J  t s l uc h a n c e  L h a t  i t  m a y  t i d e  o v e r  t e m p o r c r y  t o o d  s c e r c i r y ,  a  c o n d i t i o nx_." T h i s  d i s c u s s i o n  e m p h a s i s e s  t i r e  c a s e  o f  u n d e r f e e d i n g ,  s i n c e  t h i s  i s  t h eo n l y  c o n d i t i o n  u s e d  i n  m y  e x p e r i m e n t s .  A n  a n a l o g o u s  d e f i n i t i o n  o f ' a -d a p t a t i o n  o f  e x p e n d i t u r e  t o  u p t a k e '  c a n  b e  f o r m u l a t e d  f o r  t h e  c a s e  o fo v e r f e e d i n e .co f i non  i n  t he  na tu ra l hab i t a t  o f  many  spec ies .  Howeve r ,  such  a  de f i n i -t i o n  o f  a d a p t i v e  r e s ! r i c t i o n  o f  e x p e n d i t u r e  i n v o l v e s  f o r m i d a b l e  o p e r a -t i o n a l  d i f f i c u l t i e s .  I  s h a 1 l  r e E u r n  t o  s o m e  a s p e c t s  o f  t h i s  p r o b l e m s  i nc h a p t e r  8 .  F o r  t h e  m o m e n t  i t  w i l l  s u f f i c e  t o  s t a t e  t h a t  c o n c l u s i o n s  i nt he  t i ce ra tu re  a re  no t  unan imous  as  t o  r he  ques t i on  whe the r  o r  no tc h a n g e s  i n  m e t a b o l i s m  c a u s e d  b y  m a n i p u l a t i o n  o f  f o o d  i n L a k e ,  c a n  b ea c c o u n t e d  f o r  e x c l u s i v e l y  i n  t e r m s  o f  c h a n g e d  b o d y  m a s s  a n d  c e s s a t i o no f  f o o d  p r o c e s s i n g .  C u m m i n g  a n d  M o r r i s o n  ( 1 9 6 0 )  s t a t e :  ' T h e  t o t a l  e n e r -g y  e x p e n d i r u r e  o . [  L h e  r a t s  I e 1 I  d u r i n g  t h e  4 B  h r  f a s t  a n d  r o s e  d u r i n gre feed ing .  L t r en  t he  changes  i n  body  we ighc  and  f ood  i n t ake  we re  a l l owedfo r ,  t he  me tabo l i c  r a te  was  f ound  t o  r ema in  cons tan t  t h roughou t  t hew h o l e  e x p e r i r n e n t a l  p e r i o d t ,  I n  c o n t r a s t ,  W a l k e r  a n d  G a r r e t t  ( 1 - o 7 0 )c o n c l u d e  t h a t  e v e n  a f t e r  c o r r e c t i o n  f o r  b o d y  s i z e  r e d u c t i o n ' t h e  e n e r g yexpend i t u re  dec l i ned  marked l y  as  t he  pe r i od  o f  unde rnu t r i t i on  was  p ro -l o n g e d ' .  ( T h e y  d i d  n o t  t a k e  i n t o  a c c o u n t  c h a n g e d  c o s t s  o f  f o o d  p r o c e s -s i n g ,  b u t  E h i s  e f f e c c  w i l l  b e  c o r ) . s t a n t  f r o m  a b o u t  t h e  s e c o n d  d a y  o n -n a r d s ,  w h e r e a s  t h e  d e c r e a s e  c o n t i n u e d  b e y o n d  t h a t  t i m e , )T h e  p r e s e n t  s E u d y  i s  a  c o n t r i b u t i o n  t o  t h e  f u r t h e r  a n a l y s i s  o ft h e  p r o b l e r n  o f  a d a p t a t i o n  o f  e n e r g y  e x p e n d i t u r e  t o  u p E a k e .  C l e a r l y ,t h i s  c a n  n o t  b e  s o l v e d  b y  t h e  s t u d y  o f  t o t a l  m e t a b o l i c  r a l e  a l o n e ,  b u ton l y  by  an  ana l ys i s  o f  t he  va r i ous  componen ts  l ha t  make  up  t h i s  t o t a l .C u s t o m a r i l y  f o u r  c o m p o n e n t s  a r e  d i s t i n g u i s h e d  i n  t h e  e n e r g y  r n e t a b o l i s mo f  a  h o m e o t h e r m  ( G e s s a m a n ,  1 9 7 3 ) :  b a s a l  m e t a b o l i s m ;  m e t a b o l i s m  a b o v et h e  b a s a l  l e v e l  w h i c h  i s  u s e d  f o r  t h e r m o r e g u l a t i o n ;  m e t a b o l i s m  a s s o c i a -t e d  w i t h  a c t i v i t ' 1 ;  a n d  m e t a b o l i c  p r o c e s s e s  i n v o l v e d  i n  t h e  d i g e s t i o n  o ff o o d .  I  s h a l l  u s e  t h e  s a m e  d i v i s i o n .  H o w e v e r ,  i t  s h o u l d  b e  p o i n r e d  o u tt ha t  wha t  I  can  rneasu re  i n  my  expe r imen ts  i s  no t  t he  ra te  o f  ene rgye x p e n d i t u r e  e . g .  o n  t h e  p r o c e s s  o f  p e r f o r m i n g  m u s c u l a r  a c t i v i E y ,  b u ton l y  t he  d i f f e rence  i n  meuabo l i c  r a te  be tween  t he  pe r i od  du r i ng  wh i chtha t  ac t i v i t y  t akes  p l ace  and  pe r i ods  i n  wh i ch  t he  an ima l  i s  no t  en -g a g e d  i n  m u s c u l a r  a c E i v i t y .  T h i s  d i f f e r e n c e  g i v e s  r h e  c o s t  o f  a c r i v i r yon l y  i f  t he  o the r  componen ts  o f  ene rgy  expend i t u re  ( d i ges t i on  and  o the rp r o c e s s e s  i n  r e s L i n g  m u r a b o i i s m )  p r o c c e d  a t  r l r e  s J m e  r a L c  i r r e s p e c L i v eo f  t h e  o c c u r r e n c e  o f  r n u s c u l a r  a c t i v i t y .  T  h a v e  n o  m e a n s  o f  a s c e r t a i n i n gw h e t h e r  t h i s . i s  : ; o ,  b u t  i t  s e e m s  l r i g h l v  d o u h t f u l  f o r  i n s t a n c e  i n  v i e wn L  I h e  e f f e ,  t s  o I  s y m p a t h e r i . '  d i s c l r a r g e  a n d  e J r e n o m e d u l  l a r y  s e c r e t i o nc a u s i n g  s p l a n c h n i c  v a s c u l a r  c o n s t r i c t i o n ,  i n l r i b i t i o n  o f  l i p o g e n e s i s ,e t c .  I n  p r i n c i p l e  t h e r t f o r e  I  c e n  s t . r t e  o n l - v  t h e  d i f f e r e n c e  i n  m e t a b o -l i c  r : a t e  b e t w e e n  t h e  f  o L l o \ ^ / i n g  , ' . ) / r r 1 1 .  f . i : r t t s : .  l )  a n i m a l  r e s t i n g  i n  t h e  p o s t; r b s o r p t i v e  s L a t c ,  2 )  e n i m a l  r e s r i n g  r n d  p r o (  e s s i n g  f o o d .  3 )  a n i m a l  a c -t i v e .  F o r  b r e v i t y ,  h o w e v e r ,  I  s h a l l  d i s c u s s  m _ v  r e s u l t s  i n  t e r m s  o f  ar e s t i n g ,  a  f o o d  p r o c e s s i n g ,  s n d  - - L n  e c t i v i t y  , z o n r t ' t '  ) t ' +  c r f  m e t a b o l i s m  (( s e e  a l s o  p . 6 5 ) .  T h e  p o s s i b l e  i n f l u e n c e  o f  L h e  d e m a n d s  o f  t h e r m o r e g u l a -t i o n  o n  m e t a b o l i c  r a L c  c o u l d  b e  s t u d i e d  i n  p r i n c i p l . ' b y  m a k i n g  o b s e r -v a t i o n s  a f  d i f f e r e n t  a m b i e n t  t e m p e r i r t u r e s .  F o r  i n s t a n c e  i f  t h e  a n i m a li s  p l a c e d  i n  t h e  c o l d ,  t h i s  s h o u l d  l e a d  t o  a n  i n c r e a s e  i n  o n e  o r  m o r eo f  t h e  o L h e r  L l r r e e  c o m l ) o n e n t s  o f  m c t l b o l i s m .  S u e l r  r e m p e r d t u r e  c x p e r i -m e n L s ,  h o w e v e r ,  f e l l  o u t s i d e  t h e  s t ' o p e  o I  t h e  p r e s e n t  s t u d y .T h e  l a b o r a t o r y  r e t  w a s  c h o s e n  a s  t h e  s r r h . i e c t  o f  m v  e x p e r i m e n t s  b e -c a u s e  i t  i s  c o m m o n l y  u s e d  i n  s t u d i e s  o n  c a l t r r i c  r e g u l a c i o n .  I n t a k e  w a sc h a n p e d  i n  o n e  d i  r e c t  i , r n  n n l v  n A h p l v  r e d r r c f i o n -  A l  I  e r n c r i m e n t s  w e r eJ  t  r r s i ' r \d o n e  a t  t h e  s a m e  t e m p e r a t u r e  i n  t h e  t h e r m o n e u t r a l  z o n e  o f  f h e  r a t s  f o rE w o  r e a s o n s ,  F i r s E ,  I  w i s h e d  ! o  a v c i d  t h e  c o n r p l i c a t i o n  o f  s p e c i a l  ( a n dn o t  d i r e c t l y  m e a s u r a b l e )  h e a t  p r o d u c t i o n  f o r  t h e r m o r e g u l a t i o n .  S e c o n d ,e x p e r i m e n t s  w i t h  f o o d  d e p r i v e d  a n i m a l s  c a n  b o  c o n t i n u e d  l o n g e r  w i  t h o u tl p f h a l  p f I p c t s -  f o r  a L  t e m n e r a t u r ( , s  i n  o r  n e a r  l l r e  L h e r m r . n e u t r a l  z o D ea n i m a l s  c a n  r n o b i l i z e  m o r e  o f  t h e i r  e n e r g y  s t u r e s  a s  s h o w n  b y  d a t a  o nb i r d s  ( K e n d e i g h ,  1 9 4 5 )  a n d  r a t s  ( K l e i b e r ,  1 9 4 5 )  s t a r v e d  t i l l  d e a c h  a td i f f e r e n t  t e m p e r a t u r e s ,  C o n s e q u e n t l y  i n  m y  e x p e r i m e n t s ,  n o t w i t h s t a n d -i n g  l o n g  p e r i o d s  o f  f o o d  d e p r i v a t i o n ,  o n l v  t w o  o u t  o f  m o r e  t h a n  o n eh u n d r e d  a n i m a l s  d i e d :  t h e  o t h e r : s  c o u l d  b e  r e f e d .T h e  e n e r g y  e x p e n d i t u r e  w a s  m c a s u r e d  b y  t w  m e t h o d s :  l )  a  b a l a n c et e c h n i q u e  ( c h a p t e r  3 ) ,  c a l c u l a t i n g  e x p e n d i t u r e  f r o m  f o o d  i n t a k e ,  f a e c e sp r o d u c t i o n  a n d  c h a n g e s  i n  b o d y  r e s e r v e s ,  a n d  2 )  i n d i r e c L  c a l o r i m e t r y ,c a l c u l a t i n g  e x p e n d i t u r e  f r o m  t h e  g a s  e x c h a n g c  o f  t h c  a n i m a l s  ( c h a p r e r st4 -7 ) .  By  i nc reas ing  t he  t empo ra l  r eso lu t i on  o f  t he  l a t t e r  me thod  andcomb in i ng  i t  w i t h  o the r  r echn iques  a  de ta i l ed  ana l ys i s  o f  t oLa l  expen -d i t u r e  i n t o  i t s  c o m p o n e n t s  w a s  m a d e  p o s s i b l e ,  T h i s  p r o c e c i u r e  w i l l  b ed e s c r i b e d  i n  d e L a i l  i n  c h a p t e r  2 .I  f i r s t  de te rm ined  t he  change  i n  t o t . a r  expend i t u re  du r i ng  f ooddep r i va t i on  ( chap re r  3 ) ,  Th i s  change  \ ^ / as  f u r t he r  ana l ysed  i n  t e rms  o ft h e  e n e r g e t i c  c o n s e q u e n c e s  o f :  l )  t h e  c e s s a E i o n  o f  f o o d  p r o c e s s i n g( c h a p t e r  4 ) ; 2 )  c h a n g e s  o f  a c r i v i r y  ( c h a p t e r  5 ) ;  a n d  3 )  c h a n g e s  o ff a s t i n g  r e s t i n g  m e t a b o l i c  r a t e  ( c h a p t e r  5 ) .  F i n a l l y  t h e  c o n s e q u e n c e so f  t he  expend i t u re  changes  f o r  r egu la t i on  o f  body  t empe ra tu re  we res t u d i e d  ( c h a p t e r  7 ) .  w i t h  r e s p e c t  t o  t h e  f i r s t  p o i n r  i u  i s  r e g r e t t a b l etha t  t he  ene rgy  expend i t u re  on  f eed ing  behav iou r  cou ld  no t  be  sepa ra -red  f r om Lha t  on  o the r  behav iou r .  The re fo re  my  es t ima te  o f  t he  ene rgye x p e n d i t u r e  a s s o c i a r e d  w i t h  f o o d  p r o c e s s i n g  i n c l u d e d  o n l y  t h e  c o s t s  o fi n t e rna l  p r : ocess ing ,  wh i l e  f o r  i ns tance  f ood  hand l i ng  was  measu red  t o -ge the r  w i t h  t he  cos t s  o f  non - f eed ing  behav iou r .

Westerterp, Klaas Roelof,

University of Groningen Digital Archive

How rats economize. Energy loss in starvation

University of Groningen

   University of GroningenHow rats economizeWesterterp, Klaas RoelofIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:1976Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Westerterp, K. R. (1976). How rats economize: Energy loss in starvation. s.n.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 12-11-2019CHAPTER IGENERAL INTRODUCTIONA d u l t  a n i r n a l s ,  l i v i n g  i n  a  c o n s t a n t  b i o l o g i c a l l y  a d e q u a t e  e n v i r o n m e n t ,ma in ta i n  a  ba lance  be tween  ene rgy  up take  and  ene rgv  expend i t u re .  Thee n e r g y  s t o r e  o f  t h e  b o d y  d o e s  n o t  f l u c t u a t e  m u c h ,  a s  t h e  c o n s t a n c y  o fbody  we igh t  and  body  compos i t i on  s t r ows ,  wh i l e  t he  s to re  i s  sma l l  i nc o m p a r i s o n  t o  t h e  d a i l y  e n e r g y  t u r n o v e r ,  e s p e c i a l l y  i n  s m a l l  a n i m a l s .T h i s  c a n  b e a c l . i e v e ' J  e i t h e r  b y  c o n t r o l  o f  t h e  u p t a k e  o r  t h e  e x p e n d i t u r eo f  e n e r g y .Tha t  an  an ima l  adap t s  i t s  up rake  t o  t he  expend i t u re  o f  ene rgy  i swe i l  known .  S tud ies  on  t h i s  po in t  we re  done  by  man ipu la t i ng  ene rgy  ex -pend i t u re  v i a  a  change  o f  env i r onmen ta l  t empe ra tu re  o r  v i a  t he  amoun to f  a c t i v i t y  i m p o s e d  o n  t h e  a n i m a l .  C o r t l e  a n d  C a r l s o n  ( 1 9 5 4 )  i n c r e a s e dt h e  e n e r g y  e x p e n d i t u r e  i n  r a E s  b y  l o w e r i n g  E h e  e n v i r o n m e n t a l  t e m p e r a -t u re  f r om 25o  C ,  a  va l ue  i n  o r  c l ose  t o  t he  t he rmoneuL ra l  zone  o f  t hese. - o ^an ima l s ,  t o  5 "  C .  An ima l s  p l aced  i n  t h i s  co l d  env i r onmen !  a te  tw i ce  asmuch  as  t he i r  con t ro l s  i n  t he  wa rm env i r onmen t .  Maye r  e t  a l .  ( 1954 )  ex -e r c i s e d  r a t s  i n  a  t r e a d m i l l  w i t h  a  s p e e d  o f  o n e  m i l e  p e r  h o u r .  T h e  a n i -ma l s  p rac t i ca l l y  doub led  t he i r  f ood  i n t ake  when  t he  du ra t i on  o f  exe r -c i se  was  i nc reased  f r om one  t o  s i x  hou rs  pe r  day ,  wh i l e  bod . v  we igh t  wasma in ta i ned .  The  measu red  changes  o f  f ood  i n t ake  we re  rep resen ta t i ve  f o re n c r g y  r . r p t a k e  b e c a u s e  i n  a d u l t  r a t s  i m p o r t a n t  c h a n g e s  o f  d i g e s r i o n  e f -f i c i ency  i n  r e l a t i on  t o  l he  l eve l  o f  f ood  i n t ake  a re  neve r  f ound( N e h r i n g  e t  a l . ,  1 9 5 9 ) .  I n  b o t h  e x p e r i m e n E s  m e n t i o n e d  a  b a l a n c e  b e t w e e nup take  and  expend i t u re  was  reached  aga in  unde r  t he  new  c i r cums tances  asshown  by  t he  cons tancy  o f  body  we igh t  du r i ng  more  t han  one  week .  Mo re -ove r ,  t he  s i ze  o f  t he  rese rves  was  p robab l y  no t  i - n f l uenced  because  t h i sbody  we igh t  had  t he  no rma l  va l ue .To  conc lude ,  an  an ima l  can  change  i t s  ene rgy  up t . ake  w i t h  a t  l eas ta  f ac to r  two  f o r  adap t i ng  i t  t o  t he  expend i t u re  o f  ene rgy .T h e  p o s s i b i L i t i r  t h a t  i t n  a n i m a l  a d a p t s  i t s  e x p e n d i c u r e  t o  t h e  u p -t a k e  o [  e n e r g y  i s  o f t e n  c a l l e d  i n  q u e s t i o n .  R e c e n L l y  L e  ] 4 a g n e n  ( 1 9 7 4 )c v c n  s L A L ( ' d  t l ) a t  L I ) e  (  L \ t ) t r r r l  d f  c n c r q y  o x p e n d i t u r e  i s  c ( , n L r ; r r y  t o  w h a Lb o d y  v i e i g h t  w o u l c i  r e q u i r e  i n  v i e w  o f  h y p e r a c t i v i t y  i n  f o o d  d e p r i v a t i o na n d  h y p o a c t i v i t y  i n  o b e s i t y .  l n v e s t i g a t i o n s  o n  t h i s  p o i n L  a v a i l a b L e  i nt h e  l i t e r a t u r e  i n v o l v e d  e i t h e r  p a r t i a l  ( K e y s  e t  a L . ,  1 9 5 0 ;  G r a n d e  e ti r 1 . ,  l 9 5 B ;  M e y e r  a n d  C l a w s o n ,  1 9 6 4 ;  l " l a l k t ' r  a n d  t l a r r e t t ,  I 9 7 0 ) ,  o r  L r o m -p l e t e  ( C u m n r i n g  a n d  M o r r i s o n ,  1 9 6 0 ;  K l e i b e r ,  l 9 6 l ;  l l o r r i s o n ,  l 9 6 B )  f o o dd e p r i v a L i o n  o r ,  o n l y  i n  m a n ,  r a i s i n g  o f  i n t a k e  b y  o v e r f e e d i n g  ( l { i 1 l e rc n d  l ' 4 u m I o r d ,  1 9 6 7 \ ,  I n  t l r e s c  e x p e r i r n c n L s ,  c o n L r . l r y  t r r  t h o s e  i n  w h i e  he x p e n d i t u r e  w a s  m a n i p u l a r e d ,  b o d y  w e i g h t  d i d  n o t  r e m a i n  a !  t h e  e q u i l i -b r i u m  1 e v e 1  f o r  a d  l i b i t u m  c o n d i t i o n s .  A  n e w  b a l a n c e  b e t w e e n  i n t a k e  a n de x p e n d i t u r e  w a s  r e a c h e d  o n l y  s o m e t i m e s  ( K e y s  e t  a 1 . ,  \ r l a l k e r  a n dG . 3 r r e t t ,  l . c ,  ) .  T l r e s e  f e c L s  c o m p l  i c a L e  t h e  i n L . " r p r e t i r I i o n  o t  L l ) c  r e -s u l t s  w i E h  r e s p e c t  t o  t h e  q u e s t  i . r n  o [  r : . :  '  :  . '  .  . r t .  i ' :  , r .  , . :  -l ; , i , t t s .  S o m e  m e t a b o l i c  s a v i n q s  w i l l  r e s u l t  f r o n  t h e  m e r e  f a c t  t h a t  t h e*u n d e r I e d  s u b j e c t " ' h a s  t o  h a n d l e  a n d  d i q e s t  l e s s  f o , r d  ] l r r r € o v € r ,  d u r i n gn ; t r l  i a l  r r r  c o n r r r l p l e  l  - - : " ^ r :  -  ' !  -  t  o l r r c , r o a n  . r n d  l e T  , r r  p r / o n  n l r t <r \  L r  u i H r  r  r ( u r r s  5 ! \ \ v F (o f  t h e  c e l  l s  t h e m s e l v e s  a r e  u s e d  a s  f u e l .  B o d y  m a s s  w i l  I  d e c r e a s e ,  a n dr h i s  i s  b o u n d  t o  c 3 u s e  d  d r o p  i r L  m e L a b o l i s m .  H o w e v e r ,  I o L l o w i n g  C u m m i n ga n d  l l o r r i s o n  ( 1 . c . ) ,  T  w i L l  n o t  c e l l  r h e s e  d e . . r e a s e s  t a d e p t i v e t .R a t h e r .  I  a m  i n c l i n e d  t o  r e s t r i c t  t h i s  t e r n  t o  t h e  c a s e  w h e r e  L h e  u n -d e r I e d  a n i r n a l  s p e n d s  I c s s  f r e e  e n e r g y  o n . r  g i v e n  I u n c t i o n  ( e . g .  p r o L e i nE u r n o v e r ,  o r  m u s c u l a r  e f f o r t  f o r  a  g i v e n  b e h a v i o u r )  t h a n  a n  a d  l i b i c u mf  ed  conspec i f  i c  t -  L i t e  se t l v  r t t : t g i 1 |  and  body  , - , c rT i r t r s r l  l . i ' r r r  wou ld  do  (p .71 ) .I f  t h i s  p h e n o m e n o n  c o u l d  b e  s h o \ r n  t o  e x i s t ,  a  b a s i s  w o u l d  t h e r e b y  b el a i d  f o r  t h e  v i e w  t h a t  e v o l u t i o n  h a s  p r o v i d e d  t h e  i n d i v i d u a l  w i t h  a^ - ^  - :  ^ 1  ^ ^ . . ^ L :  r :  + "  r f  e k i  n s  o u t  i  t s  n r o v i s i o n s  i n  o r d e r  L o  i n c r e a s e  L h eL d P a u ,  r l L y  u r  l L J  t s l uc h a n c e  L h a t  i t  m a y  t i d e  o v e r  t e m p o r c r y  t o o d  s c e r c i r y ,  a  c o n d i t i o nx_." T h i s  d i s c u s s i o n  e m p h a s i s e s  t i r e  c a s e  o f  u n d e r f e e d i n g ,  s i n c e  t h i s  i s  t h eo n l y  c o n d i t i o n  u s e d  i n  m y  e x p e r i m e n t s .  A n  a n a l o g o u s  d e f i n i t i o n  o f ' a -d a p t a t i o n  o f  e x p e n d i t u r e  t o  u p t a k e '  c a n  b e  f o r m u l a t e d  f o r  t h e  c a s e  o fo v e r f e e d i n e .co f i non  i n  t he  na tu ra l hab i t a t  o f  many  spec ies .  Howeve r ,  such  a  de f i n i -t i o n  o f  a d a p t i v e  r e s ! r i c t i o n  o f  e x p e n d i t u r e  i n v o l v e s  f o r m i d a b l e  o p e r a -t i o n a l  d i f f i c u l t i e s .  I  s h a 1 l  r e E u r n  t o  s o m e  a s p e c t s  o f  t h i s  p r o b l e m s  i nc h a p t e r  8 .  F o r  t h e  m o m e n t  i t  w i l l  s u f f i c e  t o  s t a t e  t h a t  c o n c l u s i o n s  i nt he  t i ce ra tu re  a re  no t  unan imous  as  t o  r he  ques t i on  whe the r  o r  no tc h a n g e s  i n  m e t a b o l i s m  c a u s e d  b y  m a n i p u l a t i o n  o f  f o o d  i n L a k e ,  c a n  b ea c c o u n t e d  f o r  e x c l u s i v e l y  i n  t e r m s  o f  c h a n g e d  b o d y  m a s s  a n d  c e s s a t i o no f  f o o d  p r o c e s s i n g .  C u m m i n g  a n d  M o r r i s o n  ( 1 9 6 0 )  s t a t e :  ' T h e  t o t a l  e n e r -g y  e x p e n d i r u r e  o . [  L h e  r a t s  I e 1 I  d u r i n g  t h e  4 B  h r  f a s t  a n d  r o s e  d u r i n gre feed ing .  L t r en  t he  changes  i n  body  we ighc  and  f ood  i n t ake  we re  a l l owedfo r ,  t he  me tabo l i c  r a te  was  f ound  t o  r ema in  cons tan t  t h roughou t  t hew h o l e  e x p e r i r n e n t a l  p e r i o d t ,  I n  c o n t r a s t ,  W a l k e r  a n d  G a r r e t t  ( 1 - o 7 0 )c o n c l u d e  t h a t  e v e n  a f t e r  c o r r e c t i o n  f o r  b o d y  s i z e  r e d u c t i o n ' t h e  e n e r g yexpend i t u re  dec l i ned  marked l y  as  t he  pe r i od  o f  unde rnu t r i t i on  was  p ro -l o n g e d ' .  ( T h e y  d i d  n o t  t a k e  i n t o  a c c o u n t  c h a n g e d  c o s t s  o f  f o o d  p r o c e s -s i n g ,  b u t  E h i s  e f f e c c  w i l l  b e  c o r ) . s t a n t  f r o m  a b o u t  t h e  s e c o n d  d a y  o n -n a r d s ,  w h e r e a s  t h e  d e c r e a s e  c o n t i n u e d  b e y o n d  t h a t  t i m e , )T h e  p r e s e n t  s E u d y  i s  a  c o n t r i b u t i o n  t o  t h e  f u r t h e r  a n a l y s i s  o ft h e  p r o b l e r n  o f  a d a p t a t i o n  o f  e n e r g y  e x p e n d i t u r e  t o  u p E a k e .  C l e a r l y ,t h i s  c a n  n o t  b e  s o l v e d  b y  t h e  s t u d y  o f  t o t a l  m e t a b o l i c  r a l e  a l o n e ,  b u ton l y  by  an  ana l ys i s  o f  t he  va r i ous  componen ts  l ha t  make  up  t h i s  t o t a l .C u s t o m a r i l y  f o u r  c o m p o n e n t s  a r e  d i s t i n g u i s h e d  i n  t h e  e n e r g y  r n e t a b o l i s mo f  a  h o m e o t h e r m  ( G e s s a m a n ,  1 9 7 3 ) :  b a s a l  m e t a b o l i s m ;  m e t a b o l i s m  a b o v et h e  b a s a l  l e v e l  w h i c h  i s  u s e d  f o r  t h e r m o r e g u l a t i o n ;  m e t a b o l i s m  a s s o c i a -t e d  w i t h  a c t i v i t ' 1 ;  a n d  m e t a b o l i c  p r o c e s s e s  i n v o l v e d  i n  t h e  d i g e s t i o n  o ff o o d .  I  s h a l l  u s e  t h e  s a m e  d i v i s i o n .  H o w e v e r ,  i t  s h o u l d  b e  p o i n r e d  o u tt ha t  wha t  I  can  rneasu re  i n  my  expe r imen ts  i s  no t  t he  ra te  o f  ene rgye x p e n d i t u r e  e . g .  o n  t h e  p r o c e s s  o f  p e r f o r m i n g  m u s c u l a r  a c t i v i E y ,  b u ton l y  t he  d i f f e rence  i n  meuabo l i c  r a te  be tween  t he  pe r i od  du r i ng  wh i chtha t  ac t i v i t y  t akes  p l ace  and  pe r i ods  i n  wh i ch  t he  an ima l  i s  no t  en -g a g e d  i n  m u s c u l a r  a c E i v i t y .  T h i s  d i f f e r e n c e  g i v e s  r h e  c o s t  o f  a c r i v i r yon l y  i f  t he  o the r  componen ts  o f  ene rgy  expend i t u re  ( d i ges t i on  and  o the rp r o c e s s e s  i n  r e s L i n g  m u r a b o i i s m )  p r o c c e d  a t  r l r e  s J m e  r a L c  i r r e s p e c L i v eo f  t h e  o c c u r r e n c e  o f  r n u s c u l a r  a c t i v i t y .  T  h a v e  n o  m e a n s  o f  a s c e r t a i n i n gw h e t h e r  t h i s . i s  : ; o ,  b u t  i t  s e e m s  l r i g h l v  d o u h t f u l  f o r  i n s t a n c e  i n  v i e wn L  I h e  e f f e ,  t s  o I  s y m p a t h e r i . '  d i s c l r a r g e  a n d  e J r e n o m e d u l  l a r y  s e c r e t i o nc a u s i n g  s p l a n c h n i c  v a s c u l a r  c o n s t r i c t i o n ,  i n l r i b i t i o n  o f  l i p o g e n e s i s ,e t c .  I n  p r i n c i p l e  t h e r t f o r e  I  c e n  s t . r t e  o n l - v  t h e  d i f f e r e n c e  i n  m e t a b o -l i c  r : a t e  b e t w e e n  t h e  f  o L l o \ ^ / i n g  , ' . ) / r r 1 1 .  f . i : r t t s : .  l )  a n i m a l  r e s t i n g  i n  t h e  p o s t; r b s o r p t i v e  s L a t c ,  2 )  e n i m a l  r e s r i n g  r n d  p r o (  e s s i n g  f o o d .  3 )  a n i m a l  a c -t i v e .  F o r  b r e v i t y ,  h o w e v e r ,  I  s h a l l  d i s c u s s  m _ v  r e s u l t s  i n  t e r m s  o f  ar e s t i n g ,  a  f o o d  p r o c e s s i n g ,  s n d  - - L n  e c t i v i t y  , z o n r t ' t '  ) t ' +  c r f  m e t a b o l i s m  (( s e e  a l s o  p . 6 5 ) .  T h e  p o s s i b l e  i n f l u e n c e  o f  L h e  d e m a n d s  o f  t h e r m o r e g u l a -t i o n  o n  m e t a b o l i c  r a L c  c o u l d  b e  s t u d i e d  i n  p r i n c i p l . ' b y  m a k i n g  o b s e r -v a t i o n s  a f  d i f f e r e n t  a m b i e n t  t e m p e r i r t u r e s .  F o r  i n s t a n c e  i f  t h e  a n i m a li s  p l a c e d  i n  t h e  c o l d ,  t h i s  s h o u l d  l e a d  t o  a n  i n c r e a s e  i n  o n e  o r  m o r eo f  t h e  o L h e r  L l r r e e  c o m l ) o n e n t s  o f  m c t l b o l i s m .  S u e l r  r e m p e r d t u r e  c x p e r i -m e n L s ,  h o w e v e r ,  f e l l  o u t s i d e  t h e  s t ' o p e  o I  t h e  p r e s e n t  s t u d y .T h e  l a b o r a t o r y  r e t  w a s  c h o s e n  a s  t h e  s r r h . i e c t  o f  m v  e x p e r i m e n t s  b e -c a u s e  i t  i s  c o m m o n l y  u s e d  i n  s t u d i e s  o n  c a l t r r i c  r e g u l a c i o n .  I n t a k e  w a sc h a n p e d  i n  o n e  d i  r e c t  i , r n  n n l v  n A h p l v  r e d r r c f i o n -  A l  I  e r n c r i m e n t s  w e r eJ  t  r r s i ' r \d o n e  a t  t h e  s a m e  t e m p e r a t u r e  i n  t h e  t h e r m o n e u t r a l  z o n e  o f  f h e  r a t s  f o rE w o  r e a s o n s ,  F i r s E ,  I  w i s h e d  ! o  a v c i d  t h e  c o n r p l i c a t i o n  o f  s p e c i a l  ( a n dn o t  d i r e c t l y  m e a s u r a b l e )  h e a t  p r o d u c t i o n  f o r  t h e r m o r e g u l a t i o n .  S e c o n d ,e x p e r i m e n t s  w i t h  f o o d  d e p r i v e d  a n i m a l s  c a n  b o  c o n t i n u e d  l o n g e r  w i  t h o u tl p f h a l  p f I p c t s -  f o r  a L  t e m n e r a t u r ( , s  i n  o r  n e a r  l l r e  L h e r m r . n e u t r a l  z o D ea n i m a l s  c a n  r n o b i l i z e  m o r e  o f  t h e i r  e n e r g y  s t u r e s  a s  s h o w n  b y  d a t a  o nb i r d s  ( K e n d e i g h ,  1 9 4 5 )  a n d  r a t s  ( K l e i b e r ,  1 9 4 5 )  s t a r v e d  t i l l  d e a c h  a td i f f e r e n t  t e m p e r a t u r e s ,  C o n s e q u e n t l y  i n  m y  e x p e r i m e n t s ,  n o t w i t h s t a n d -i n g  l o n g  p e r i o d s  o f  f o o d  d e p r i v a t i o n ,  o n l v  t w o  o u t  o f  m o r e  t h a n  o n eh u n d r e d  a n i m a l s  d i e d :  t h e  o t h e r : s  c o u l d  b e  r e f e d .T h e  e n e r g y  e x p e n d i t u r e  w a s  m c a s u r e d  b y  t w  m e t h o d s :  l )  a  b a l a n c et e c h n i q u e  ( c h a p t e r  3 ) ,  c a l c u l a t i n g  e x p e n d i t u r e  f r o m  f o o d  i n t a k e ,  f a e c e sp r o d u c t i o n  a n d  c h a n g e s  i n  b o d y  r e s e r v e s ,  a n d  2 )  i n d i r e c L  c a l o r i m e t r y ,c a l c u l a t i n g  e x p e n d i t u r e  f r o m  t h e  g a s  e x c h a n g c  o f  t h c  a n i m a l s  ( c h a p r e r st4 -7 ) .  By  i nc reas ing  t he  t empo ra l  r eso lu t i on  o f  t he  l a t t e r  me thod  andcomb in i ng  i t  w i t h  o the r  r echn iques  a  de ta i l ed  ana l ys i s  o f  t oLa l  expen -d i t u r e  i n t o  i t s  c o m p o n e n t s  w a s  m a d e  p o s s i b l e ,  T h i s  p r o c e c i u r e  w i l l  b ed e s c r i b e d  i n  d e L a i l  i n  c h a p t e r  2 .I  f i r s t  de te rm ined  t he  change  i n  t o t . a r  expend i t u re  du r i ng  f ooddep r i va t i on  ( chap re r  3 ) ,  Th i s  change  \ ^ / as  f u r t he r  ana l ysed  i n  t e rms  o ft h e  e n e r g e t i c  c o n s e q u e n c e s  o f :  l )  t h e  c e s s a E i o n  o f  f o o d  p r o c e s s i n g( c h a p t e r  4 ) ; 2 )  c h a n g e s  o f  a c r i v i r y  ( c h a p t e r  5 ) ;  a n d  3 )  c h a n g e s  o ff a s t i n g  r e s t i n g  m e t a b o l i c  r a t e  ( c h a p t e r  5 ) .  F i n a l l y  t h e  c o n s e q u e n c e so f  t he  expend i t u re  changes  f o r  r egu la t i on  o f  body  t empe ra tu re  we res t u d i e d  ( c h a p t e r  7 ) .  w i t h  r e s p e c t  t o  t h e  f i r s t  p o i n r  i u  i s  r e g r e t t a b l etha t  t he  ene rgy  expend i t u re  on  f eed ing  behav iou r  cou ld  no t  be  sepa ra -red  f r om Lha t  on  o the r  behav iou r .  The re fo re  my  es t ima te  o f  t he  ene rgye x p e n d i t u r e  a s s o c i a r e d  w i t h  f o o d  p r o c e s s i n g  i n c l u d e d  o n l y  t h e  c o s t s  o fi n t e rna l  p r : ocess ing ,  wh i l e  f o r  i ns tance  f ood  hand l i ng  was  measu red  t o -ge the r  w i t h  t he  cos t s  o f  non - f eed ing  behav iou r .

   University of GroningenHow rats economizeWesterterp, Klaas RoelofIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:1976Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Westerterp, K. R. (1976). How rats economize: Energy loss in starvation. s.n.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 08-06-2022CHAPTER IGENERAL INTRODUCTIONA d u l t  a n i r n a l s ,  l i v i n g  i n  a  c o n s t a n t  b i o l o g i c a l l y  a d e q u a t e  e n v i r o n m e n t ,ma in ta i n  a  ba lance  be tween  ene rgy  up take  and  ene rgv  expend i t u re .  Thee n e r g y  s t o r e  o f  t h e  b o d y  d o e s  n o t  f l u c t u a t e  m u c h ,  a s  t h e  c o n s t a n c y  o fbody  we igh t  and  body  compos i t i on  s t r ows ,  wh i l e  t he  s to re  i s  sma l l  i nc o m p a r i s o n  t o  t h e  d a i l y  e n e r g y  t u r n o v e r ,  e s p e c i a l l y  i n  s m a l l  a n i m a l s .T h i s  c a n  b e a c l . i e v e ' J  e i t h e r  b y  c o n t r o l  o f  t h e  u p t a k e  o r  t h e  e x p e n d i t u r eo f  e n e r g y .Tha t  an  an ima l  adap t s  i t s  up rake  t o  t he  expend i t u re  o f  ene rgy  i swe i l  known .  S tud ies  on  t h i s  po in t  we re  done  by  man ipu la t i ng  ene rgy  ex -pend i t u re  v i a  a  change  o f  env i r onmen ta l  t empe ra tu re  o r  v i a  t he  amoun to f  a c t i v i t y  i m p o s e d  o n  t h e  a n i m a l .  C o r t l e  a n d  C a r l s o n  ( 1 9 5 4 )  i n c r e a s e dt h e  e n e r g y  e x p e n d i t u r e  i n  r a E s  b y  l o w e r i n g  E h e  e n v i r o n m e n t a l  t e m p e r a -t u re  f r om 25o  C ,  a  va l ue  i n  o r  c l ose  t o  t he  t he rmoneuL ra l  zone  o f  t hese. - o ^an ima l s ,  t o  5 "  C .  An ima l s  p l aced  i n  t h i s  co l d  env i r onmen !  a te  tw i ce  asmuch  as  t he i r  con t ro l s  i n  t he  wa rm env i r onmen t .  Maye r  e t  a l .  ( 1954 )  ex -e r c i s e d  r a t s  i n  a  t r e a d m i l l  w i t h  a  s p e e d  o f  o n e  m i l e  p e r  h o u r .  T h e  a n i -ma l s  p rac t i ca l l y  doub led  t he i r  f ood  i n t ake  when  t he  du ra t i on  o f  exe r -c i se  was  i nc reased  f r om one  t o  s i x  hou rs  pe r  day ,  wh i l e  bod . v  we igh t  wasma in ta i ned .  The  measu red  changes  o f  f ood  i n t ake  we re  rep resen ta t i ve  f o re n c r g y  r . r p t a k e  b e c a u s e  i n  a d u l t  r a t s  i m p o r t a n t  c h a n g e s  o f  d i g e s r i o n  e f -f i c i ency  i n  r e l a t i on  t o  l he  l eve l  o f  f ood  i n t ake  a re  neve r  f ound( N e h r i n g  e t  a l . ,  1 9 5 9 ) .  I n  b o t h  e x p e r i m e n E s  m e n t i o n e d  a  b a l a n c e  b e t w e e nup take  and  expend i t u re  was  reached  aga in  unde r  t he  new  c i r cums tances  asshown  by  t he  cons tancy  o f  body  we igh t  du r i ng  more  t han  one  week .  Mo re -ove r ,  t he  s i ze  o f  t he  rese rves  was  p robab l y  no t  i - n f l uenced  because  t h i sbody  we igh t  had  t he  no rma l  va l ue .To  conc lude ,  an  an ima l  can  change  i t s  ene rgy  up t . ake  w i t h  a t  l eas ta  f ac to r  two  f o r  adap t i ng  i t  t o  t he  expend i t u re  o f  ene rgy .T h e  p o s s i b i L i t i r  t h a t  i t n  a n i m a l  a d a p t s  i t s  e x p e n d i c u r e  t o  t h e  u p -t a k e  o [  e n e r g y  i s  o f t e n  c a l l e d  i n  q u e s t i o n .  R e c e n L l y  L e  ] 4 a g n e n  ( 1 9 7 4 )c v c n  s L A L ( ' d  t l ) a t  L I ) e  (  L \ t ) t r r r l  d f  c n c r q y  o x p e n d i t u r e  i s  c ( , n L r ; r r y  t o  w h a Lb o d y  v i e i g h t  w o u l c i  r e q u i r e  i n  v i e w  o f  h y p e r a c t i v i t y  i n  f o o d  d e p r i v a t i o na n d  h y p o a c t i v i t y  i n  o b e s i t y .  l n v e s t i g a t i o n s  o n  t h i s  p o i n L  a v a i l a b L e  i nt h e  l i t e r a t u r e  i n v o l v e d  e i t h e r  p a r t i a l  ( K e y s  e t  a L . ,  1 9 5 0 ;  G r a n d e  e ti r 1 . ,  l 9 5 B ;  M e y e r  a n d  C l a w s o n ,  1 9 6 4 ;  l " l a l k t ' r  a n d  t l a r r e t t ,  I 9 7 0 ) ,  o r  L r o m -p l e t e  ( C u m n r i n g  a n d  M o r r i s o n ,  1 9 6 0 ;  K l e i b e r ,  l 9 6 l ;  l l o r r i s o n ,  l 9 6 B )  f o o dd e p r i v a L i o n  o r ,  o n l y  i n  m a n ,  r a i s i n g  o f  i n t a k e  b y  o v e r f e e d i n g  ( l { i 1 l e rc n d  l ' 4 u m I o r d ,  1 9 6 7 \ ,  I n  t l r e s c  e x p e r i r n c n L s ,  c o n L r . l r y  t r r  t h o s e  i n  w h i e  he x p e n d i t u r e  w a s  m a n i p u l a r e d ,  b o d y  w e i g h t  d i d  n o t  r e m a i n  a !  t h e  e q u i l i -b r i u m  1 e v e 1  f o r  a d  l i b i t u m  c o n d i t i o n s .  A  n e w  b a l a n c e  b e t w e e n  i n t a k e  a n de x p e n d i t u r e  w a s  r e a c h e d  o n l y  s o m e t i m e s  ( K e y s  e t  a 1 . ,  \ r l a l k e r  a n dG . 3 r r e t t ,  l . c ,  ) .  T l r e s e  f e c L s  c o m p l  i c a L e  t h e  i n L . " r p r e t i r I i o n  o t  L l ) c  r e -s u l t s  w i E h  r e s p e c t  t o  t h e  q u e s t  i . r n  o [  r : . :  '  :  . '  .  . r t .  i ' :  , r .  , . :  -l ; , i , t t s .  S o m e  m e t a b o l i c  s a v i n q s  w i l l  r e s u l t  f r o n  t h e  m e r e  f a c t  t h a t  t h e*u n d e r I e d  s u b j e c t " ' h a s  t o  h a n d l e  a n d  d i q e s t  l e s s  f o , r d  ] l r r r € o v € r ,  d u r i n gn ; t r l  i a l  r r r  c o n r r r l p l e  l  - - : " ^ r :  -  ' !  -  t  o l r r c , r o a n  . r n d  l e T  , r r  p r / o n  n l r t <r \  L r  u i H r  r  r ( u r r s  5 ! \ \ v F (o f  t h e  c e l  l s  t h e m s e l v e s  a r e  u s e d  a s  f u e l .  B o d y  m a s s  w i l  I  d e c r e a s e ,  a n dr h i s  i s  b o u n d  t o  c 3 u s e  d  d r o p  i r L  m e L a b o l i s m .  H o w e v e r ,  I o L l o w i n g  C u m m i n ga n d  l l o r r i s o n  ( 1 . c . ) ,  T  w i L l  n o t  c e l l  r h e s e  d e . . r e a s e s  t a d e p t i v e t .R a t h e r .  I  a m  i n c l i n e d  t o  r e s t r i c t  t h i s  t e r n  t o  t h e  c a s e  w h e r e  L h e  u n -d e r I e d  a n i r n a l  s p e n d s  I c s s  f r e e  e n e r g y  o n . r  g i v e n  I u n c t i o n  ( e . g .  p r o L e i nE u r n o v e r ,  o r  m u s c u l a r  e f f o r t  f o r  a  g i v e n  b e h a v i o u r )  t h a n  a n  a d  l i b i c u mf  ed  conspec i f  i c  t -  L i t e  se t l v  r t t : t g i 1 |  and  body  , - , c rT i r t r s r l  l . i ' r r r  wou ld  do  (p .71 ) .I f  t h i s  p h e n o m e n o n  c o u l d  b e  s h o \ r n  t o  e x i s t ,  a  b a s i s  w o u l d  t h e r e b y  b el a i d  f o r  t h e  v i e w  t h a t  e v o l u t i o n  h a s  p r o v i d e d  t h e  i n d i v i d u a l  w i t h  a^ - ^  - :  ^ 1  ^ ^ . . ^ L :  r :  + "  r f  e k i  n s  o u t  i  t s  n r o v i s i o n s  i n  o r d e r  L o  i n c r e a s e  L h eL d P a u ,  r l L y  u r  l L J  t s l uc h a n c e  L h a t  i t  m a y  t i d e  o v e r  t e m p o r c r y  t o o d  s c e r c i r y ,  a  c o n d i t i o nx_." T h i s  d i s c u s s i o n  e m p h a s i s e s  t i r e  c a s e  o f  u n d e r f e e d i n g ,  s i n c e  t h i s  i s  t h eo n l y  c o n d i t i o n  u s e d  i n  m y  e x p e r i m e n t s .  A n  a n a l o g o u s  d e f i n i t i o n  o f ' a -d a p t a t i o n  o f  e x p e n d i t u r e  t o  u p t a k e '  c a n  b e  f o r m u l a t e d  f o r  t h e  c a s e  o fo v e r f e e d i n e .co f i non  i n  t he  na tu ra l hab i t a t  o f  many  spec ies .  Howeve r ,  such  a  de f i n i -t i o n  o f  a d a p t i v e  r e s ! r i c t i o n  o f  e x p e n d i t u r e  i n v o l v e s  f o r m i d a b l e  o p e r a -t i o n a l  d i f f i c u l t i e s .  I  s h a 1 l  r e E u r n  t o  s o m e  a s p e c t s  o f  t h i s  p r o b l e m s  i nc h a p t e r  8 .  F o r  t h e  m o m e n t  i t  w i l l  s u f f i c e  t o  s t a t e  t h a t  c o n c l u s i o n s  i nt he  t i ce ra tu re  a re  no t  unan imous  as  t o  r he  ques t i on  whe the r  o r  no tc h a n g e s  i n  m e t a b o l i s m  c a u s e d  b y  m a n i p u l a t i o n  o f  f o o d  i n L a k e ,  c a n  b ea c c o u n t e d  f o r  e x c l u s i v e l y  i n  t e r m s  o f  c h a n g e d  b o d y  m a s s  a n d  c e s s a t i o no f  f o o d  p r o c e s s i n g .  C u m m i n g  a n d  M o r r i s o n  ( 1 9 6 0 )  s t a t e :  ' T h e  t o t a l  e n e r -g y  e x p e n d i r u r e  o . [  L h e  r a t s  I e 1 I  d u r i n g  t h e  4 B  h r  f a s t  a n d  r o s e  d u r i n gre feed ing .  L t r en  t he  changes  i n  body  we ighc  and  f ood  i n t ake  we re  a l l owedfo r ,  t he  me tabo l i c  r a te  was  f ound  t o  r ema in  cons tan t  t h roughou t  t hew h o l e  e x p e r i r n e n t a l  p e r i o d t ,  I n  c o n t r a s t ,  W a l k e r  a n d  G a r r e t t  ( 1 - o 7 0 )c o n c l u d e  t h a t  e v e n  a f t e r  c o r r e c t i o n  f o r  b o d y  s i z e  r e d u c t i o n ' t h e  e n e r g yexpend i t u re  dec l i ned  marked l y  as  t he  pe r i od  o f  unde rnu t r i t i on  was  p ro -l o n g e d ' .  ( T h e y  d i d  n o t  t a k e  i n t o  a c c o u n t  c h a n g e d  c o s t s  o f  f o o d  p r o c e s -s i n g ,  b u t  E h i s  e f f e c c  w i l l  b e  c o r ) . s t a n t  f r o m  a b o u t  t h e  s e c o n d  d a y  o n -n a r d s ,  w h e r e a s  t h e  d e c r e a s e  c o n t i n u e d  b e y o n d  t h a t  t i m e , )T h e  p r e s e n t  s E u d y  i s  a  c o n t r i b u t i o n  t o  t h e  f u r t h e r  a n a l y s i s  o ft h e  p r o b l e r n  o f  a d a p t a t i o n  o f  e n e r g y  e x p e n d i t u r e  t o  u p E a k e .  C l e a r l y ,t h i s  c a n  n o t  b e  s o l v e d  b y  t h e  s t u d y  o f  t o t a l  m e t a b o l i c  r a l e  a l o n e ,  b u ton l y  by  an  ana l ys i s  o f  t he  va r i ous  componen ts  l ha t  make  up  t h i s  t o t a l .C u s t o m a r i l y  f o u r  c o m p o n e n t s  a r e  d i s t i n g u i s h e d  i n  t h e  e n e r g y  r n e t a b o l i s mo f  a  h o m e o t h e r m  ( G e s s a m a n ,  1 9 7 3 ) :  b a s a l  m e t a b o l i s m ;  m e t a b o l i s m  a b o v et h e  b a s a l  l e v e l  w h i c h  i s  u s e d  f o r  t h e r m o r e g u l a t i o n ;  m e t a b o l i s m  a s s o c i a -t e d  w i t h  a c t i v i t ' 1 ;  a n d  m e t a b o l i c  p r o c e s s e s  i n v o l v e d  i n  t h e  d i g e s t i o n  o ff o o d .  I  s h a l l  u s e  t h e  s a m e  d i v i s i o n .  H o w e v e r ,  i t  s h o u l d  b e  p o i n r e d  o u tt ha t  wha t  I  can  rneasu re  i n  my  expe r imen ts  i s  no t  t he  ra te  o f  ene rgye x p e n d i t u r e  e . g .  o n  t h e  p r o c e s s  o f  p e r f o r m i n g  m u s c u l a r  a c t i v i E y ,  b u ton l y  t he  d i f f e rence  i n  meuabo l i c  r a te  be tween  t he  pe r i od  du r i ng  wh i chtha t  ac t i v i t y  t akes  p l ace  and  pe r i ods  i n  wh i ch  t he  an ima l  i s  no t  en -g a g e d  i n  m u s c u l a r  a c E i v i t y .  T h i s  d i f f e r e n c e  g i v e s  r h e  c o s t  o f  a c r i v i r yon l y  i f  t he  o the r  componen ts  o f  ene rgy  expend i t u re  ( d i ges t i on  and  o the rp r o c e s s e s  i n  r e s L i n g  m u r a b o i i s m )  p r o c c e d  a t  r l r e  s J m e  r a L c  i r r e s p e c L i v eo f  t h e  o c c u r r e n c e  o f  r n u s c u l a r  a c t i v i t y .  T  h a v e  n o  m e a n s  o f  a s c e r t a i n i n gw h e t h e r  t h i s . i s  : ; o ,  b u t  i t  s e e m s  l r i g h l v  d o u h t f u l  f o r  i n s t a n c e  i n  v i e wn L  I h e  e f f e ,  t s  o I  s y m p a t h e r i . '  d i s c l r a r g e  a n d  e J r e n o m e d u l  l a r y  s e c r e t i o nc a u s i n g  s p l a n c h n i c  v a s c u l a r  c o n s t r i c t i o n ,  i n l r i b i t i o n  o f  l i p o g e n e s i s ,e t c .  I n  p r i n c i p l e  t h e r t f o r e  I  c e n  s t . r t e  o n l - v  t h e  d i f f e r e n c e  i n  m e t a b o -l i c  r : a t e  b e t w e e n  t h e  f  o L l o \ ^ / i n g  , ' . ) / r r 1 1 .  f . i : r t t s : .  l )  a n i m a l  r e s t i n g  i n  t h e  p o s t; r b s o r p t i v e  s L a t c ,  2 )  e n i m a l  r e s r i n g  r n d  p r o (  e s s i n g  f o o d .  3 )  a n i m a l  a c -t i v e .  F o r  b r e v i t y ,  h o w e v e r ,  I  s h a l l  d i s c u s s  m _ v  r e s u l t s  i n  t e r m s  o f  ar e s t i n g ,  a  f o o d  p r o c e s s i n g ,  s n d  - - L n  e c t i v i t y  , z o n r t ' t '  ) t ' +  c r f  m e t a b o l i s m  (( s e e  a l s o  p . 6 5 ) .  T h e  p o s s i b l e  i n f l u e n c e  o f  L h e  d e m a n d s  o f  t h e r m o r e g u l a -t i o n  o n  m e t a b o l i c  r a L c  c o u l d  b e  s t u d i e d  i n  p r i n c i p l . ' b y  m a k i n g  o b s e r -v a t i o n s  a f  d i f f e r e n t  a m b i e n t  t e m p e r i r t u r e s .  F o r  i n s t a n c e  i f  t h e  a n i m a li s  p l a c e d  i n  t h e  c o l d ,  t h i s  s h o u l d  l e a d  t o  a n  i n c r e a s e  i n  o n e  o r  m o r eo f  t h e  o L h e r  L l r r e e  c o m l ) o n e n t s  o f  m c t l b o l i s m .  S u e l r  r e m p e r d t u r e  c x p e r i -m e n L s ,  h o w e v e r ,  f e l l  o u t s i d e  t h e  s t ' o p e  o I  t h e  p r e s e n t  s t u d y .T h e  l a b o r a t o r y  r e t  w a s  c h o s e n  a s  t h e  s r r h . i e c t  o f  m v  e x p e r i m e n t s  b e -c a u s e  i t  i s  c o m m o n l y  u s e d  i n  s t u d i e s  o n  c a l t r r i c  r e g u l a c i o n .  I n t a k e  w a sc h a n p e d  i n  o n e  d i  r e c t  i , r n  n n l v  n A h p l v  r e d r r c f i o n -  A l  I  e r n c r i m e n t s  w e r eJ  t  r r s i ' r \d o n e  a t  t h e  s a m e  t e m p e r a t u r e  i n  t h e  t h e r m o n e u t r a l  z o n e  o f  f h e  r a t s  f o rE w o  r e a s o n s ,  F i r s E ,  I  w i s h e d  ! o  a v c i d  t h e  c o n r p l i c a t i o n  o f  s p e c i a l  ( a n dn o t  d i r e c t l y  m e a s u r a b l e )  h e a t  p r o d u c t i o n  f o r  t h e r m o r e g u l a t i o n .  S e c o n d ,e x p e r i m e n t s  w i t h  f o o d  d e p r i v e d  a n i m a l s  c a n  b o  c o n t i n u e d  l o n g e r  w i  t h o u tl p f h a l  p f I p c t s -  f o r  a L  t e m n e r a t u r ( , s  i n  o r  n e a r  l l r e  L h e r m r . n e u t r a l  z o D ea n i m a l s  c a n  r n o b i l i z e  m o r e  o f  t h e i r  e n e r g y  s t u r e s  a s  s h o w n  b y  d a t a  o nb i r d s  ( K e n d e i g h ,  1 9 4 5 )  a n d  r a t s  ( K l e i b e r ,  1 9 4 5 )  s t a r v e d  t i l l  d e a c h  a td i f f e r e n t  t e m p e r a t u r e s ,  C o n s e q u e n t l y  i n  m y  e x p e r i m e n t s ,  n o t w i t h s t a n d -i n g  l o n g  p e r i o d s  o f  f o o d  d e p r i v a t i o n ,  o n l v  t w o  o u t  o f  m o r e  t h a n  o n eh u n d r e d  a n i m a l s  d i e d :  t h e  o t h e r : s  c o u l d  b e  r e f e d .T h e  e n e r g y  e x p e n d i t u r e  w a s  m c a s u r e d  b y  t w  m e t h o d s :  l )  a  b a l a n c et e c h n i q u e  ( c h a p t e r  3 ) ,  c a l c u l a t i n g  e x p e n d i t u r e  f r o m  f o o d  i n t a k e ,  f a e c e sp r o d u c t i o n  a n d  c h a n g e s  i n  b o d y  r e s e r v e s ,  a n d  2 )  i n d i r e c L  c a l o r i m e t r y ,c a l c u l a t i n g  e x p e n d i t u r e  f r o m  t h e  g a s  e x c h a n g c  o f  t h c  a n i m a l s  ( c h a p r e r st4 -7 ) .  By  i nc reas ing  t he  t empo ra l  r eso lu t i on  o f  t he  l a t t e r  me thod  andcomb in i ng  i t  w i t h  o the r  r echn iques  a  de ta i l ed  ana l ys i s  o f  t oLa l  expen -d i t u r e  i n t o  i t s  c o m p o n e n t s  w a s  m a d e  p o s s i b l e ,  T h i s  p r o c e c i u r e  w i l l  b ed e s c r i b e d  i n  d e L a i l  i n  c h a p t e r  2 .I  f i r s t  de te rm ined  t he  change  i n  t o t . a r  expend i t u re  du r i ng  f ooddep r i va t i on  ( chap re r  3 ) ,  Th i s  change  \ ^ / as  f u r t he r  ana l ysed  i n  t e rms  o ft h e  e n e r g e t i c  c o n s e q u e n c e s  o f :  l )  t h e  c e s s a E i o n  o f  f o o d  p r o c e s s i n g( c h a p t e r  4 ) ; 2 )  c h a n g e s  o f  a c r i v i r y  ( c h a p t e r  5 ) ;  a n d  3 )  c h a n g e s  o ff a s t i n g  r e s t i n g  m e t a b o l i c  r a t e  ( c h a p t e r  5 ) .  F i n a l l y  t h e  c o n s e q u e n c e so f  t he  expend i t u re  changes  f o r  r egu la t i on  o f  body  t empe ra tu re  we res t u d i e d  ( c h a p t e r  7 ) .  w i t h  r e s p e c t  t o  t h e  f i r s t  p o i n r  i u  i s  r e g r e t t a b l etha t  t he  ene rgy  expend i t u re  on  f eed ing  behav iou r  cou ld  no t  be  sepa ra -red  f r om Lha t  on  o the r  behav iou r .  The re fo re  my  es t ima te  o f  t he  ene rgye x p e n d i t u r e  a s s o c i a r e d  w i t h  f o o d  p r o c e s s i n g  i n c l u d e d  o n l y  t h e  c o s t s  o fi n t e rna l  p r : ocess ing ,  wh i l e  f o r  i ns tance  f ood  hand l i ng  was  measu red  t o -ge the r  w i t h  t he  cos t s  o f  non - f eed ing  behav iou r .

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 University of Groningen
How rats economize
Westerterp, Klaas Roelof
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1976
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Westerterp, K. R. (1976). How rats economize: Energy loss in starvation s.n.
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Download date: 11-02-2018
CHAPTER I
GENERAL INTRODUCTION
A d u l t  a n i r n a l s ,  l i v i n g  i n  a  c o n s t a n t  b i o l o g i c a l l y  a d e q u a t e  e n v i r o n m e n t ,
ma in ta i n  a  ba lance  be tween  ene rgy  up take  and  ene rgv  expend i t u re .  The
e n e r g y  s t o r e  o f  t h e  b o d y  d o e s  n o t  f l u c t u a t e  m u c h ,  a s  t h e  c o n s t a n c y  o f
body  we igh t  and  body  compos i t i on  s t r ows ,  wh i l e  t he  s to re  i s  sma l l  i n
c o m p a r i s o n  t o  t h e  d a i l y  e n e r g y  t u r n o v e r ,  e s p e c i a l l y  i n  s m a l l  a n i m a l s .
T h i s  c a n  b e a c l . i e v e ' J  e i t h e r  b y  c o n t r o l  o f  t h e  u p t a k e  o r  t h e  e x p e n d i t u r e
o f  e n e r g y .
Tha t  an  an ima l  adap t s  i t s  up rake  t o  t he  expend i t u re  o f  ene rgy  i s
we i l  known .  S tud ies  on  t h i s  po in t  we re  done  by  man ipu la t i ng  ene rgy  ex -
pend i t u re  v i a  a  change  o f  env i r onmen ta l  t empe ra tu re  o r  v i a  t he  amoun t
o f  a c t i v i t y  i m p o s e d  o n  t h e  a n i m a l .  C o r t l e  a n d  C a r l s o n  ( 1 9 5 4 )  i n c r e a s e d
t h e  e n e r g y  e x p e n d i t u r e  i n  r a E s  b y  l o w e r i n g  E h e  e n v i r o n m e n t a l  t e m p e r a -
t u re  f r om 25o  C ,  a  va l ue  i n  o r  c l ose  t o  t he  t he rmoneuL ra l  zone  o f  t hese
. - o ^
an ima l s ,  t o  5 "  C .  An ima l s  p l aced  i n  t h i s  co l d  env i r onmen !  a te  tw i ce  as
much  as  t he i r  con t ro l s  i n  t he  wa rm env i r onmen t .  Maye r  e t  a l .  ( 1954 )  ex -
e r c i s e d  r a t s  i n  a  t r e a d m i l l  w i t h  a  s p e e d  o f  o n e  m i l e  p e r  h o u r .  T h e  a n i -
ma l s  p rac t i ca l l y  doub led  t he i r  f ood  i n t ake  when  t he  du ra t i on  o f  exe r -
c i se  was  i nc reased  f r om one  t o  s i x  hou rs  pe r  day ,  wh i l e  bod . v  we igh t  was
ma in ta i ned .  The  measu red  changes  o f  f ood  i n t ake  we re  rep resen ta t i ve  f o r
e n c r g y  r . r p t a k e  b e c a u s e  i n  a d u l t  r a t s  i m p o r t a n t  c h a n g e s  o f  d i g e s r i o n  e f -
f i c i ency  i n  r e l a t i on  t o  l he  l eve l  o f  f ood  i n t ake  a re  neve r  f ound
( N e h r i n g  e t  a l . ,  1 9 5 9 ) .  I n  b o t h  e x p e r i m e n E s  m e n t i o n e d  a  b a l a n c e  b e t w e e n
up take  and  expend i t u re  was  reached  aga in  unde r  t he  new  c i r cums tances  as
shown  by  t he  cons tancy  o f  body  we igh t  du r i ng  more  t han  one  week .  Mo re -
ove r ,  t he  s i ze  o f  t he  rese rves  was  p robab l y  no t  i - n f l uenced  because  t h i s
body  we igh t  had  t he  no rma l  va l ue .
To  conc lude ,  an  an ima l  can  change  i t s  ene rgy  up t . ake  w i t h  a t  l eas t
a  f ac to r  two  f o r  adap t i ng  i t  t o  t he  expend i t u re  o f  ene rgy .
T h e  p o s s i b i L i t i r  t h a t  i t n  a n i m a l  a d a p t s  i t s  e x p e n d i c u r e  t o  t h e  u p -
t a k e  o [  e n e r g y  i s  o f t e n  c a l l e d  i n  q u e s t i o n .  R e c e n L l y  L e  ] 4 a g n e n  ( 1 9 7 4 )
c v c n  s L A L ( ' d  t l ) a t  L I ) e  (  L \ t ) t r r r l  d f  c n c r q y  o x p e n d i t u r e  i s  c ( , n L r ; r r y  t o  w h a L
b o d y  v i e i g h t  w o u l c i  r e q u i r e  i n  v i e w  o f  h y p e r a c t i v i t y  i n  f o o d  d e p r i v a t i o n
a n d  h y p o a c t i v i t y  i n  o b e s i t y .  l n v e s t i g a t i o n s  o n  t h i s  p o i n L  a v a i l a b L e  i n
t h e  l i t e r a t u r e  i n v o l v e d  e i t h e r  p a r t i a l  ( K e y s  e t  a L . ,  1 9 5 0 ;  G r a n d e  e t
i r 1 . ,  l 9 5 B ;  M e y e r  a n d  C l a w s o n ,  1 9 6 4 ;  l " l a l k t ' r  a n d  t l a r r e t t ,  I 9 7 0 ) ,  o r  L r o m -
p l e t e  ( C u m n r i n g  a n d  M o r r i s o n ,  1 9 6 0 ;  K l e i b e r ,  l 9 6 l ;  l l o r r i s o n ,  l 9 6 B )  f o o d
d e p r i v a L i o n  o r ,  o n l y  i n  m a n ,  r a i s i n g  o f  i n t a k e  b y  o v e r f e e d i n g  ( l { i 1 l e r
c n d  l ' 4 u m I o r d ,  1 9 6 7 \ ,  I n  t l r e s c  e x p e r i r n c n L s ,  c o n L r . l r y  t r r  t h o s e  i n  w h i e  h
e x p e n d i t u r e  w a s  m a n i p u l a r e d ,  b o d y  w e i g h t  d i d  n o t  r e m a i n  a !  t h e  e q u i l i -
b r i u m  1 e v e 1  f o r  a d  l i b i t u m  c o n d i t i o n s .  A  n e w  b a l a n c e  b e t w e e n  i n t a k e  a n d
e x p e n d i t u r e  w a s  r e a c h e d  o n l y  s o m e t i m e s  ( K e y s  e t  a 1 . ,  \ r l a l k e r  a n d
G . 3 r r e t t ,  l . c ,  ) .  T l r e s e  f e c L s  c o m p l  i c a L e  t h e  i n L . " r p r e t i r I i o n  o t  L l ) c  r e -
s u l t s  w i E h  r e s p e c t  t o  t h e  q u e s t  i . r n  o [  r : . :  '  :  
. '  
.  
. r t .  i ' :  , r .  , . :  -
l ; , i , t t s .  S o m e  m e t a b o l i c  s a v i n q s  w i l l  r e s u l t  f r o n  t h e  m e r e  f a c t  t h a t  t h e
*
u n d e r I e d  s u b j e c t " ' h a s  t o  h a n d l e  a n d  d i q e s t  l e s s  f o , r d  ] l r r r € o v € r ,  d u r i n g
n ; t r l  i a l  r r r  c o n r r r l p l e  l  - - : " ^ r :  -  ' !  -  t  o l r r c , r o a n  . r n d  l e T  , r r  p r / o n  n l r t <r \  L r  u i H r  r  r ( u r r s  5 ! \ \ v F (
o f  t h e  c e l  l s  t h e m s e l v e s  a r e  u s e d  a s  f u e l .  B o d y  m a s s  w i l  I  d e c r e a s e ,  a n d
r h i s  i s  b o u n d  t o  c 3 u s e  d  d r o p  i r L  m e L a b o l i s m .  H o w e v e r ,  I o L l o w i n g  C u m m i n g
a n d  l l o r r i s o n  ( 1 . c . ) ,  T  w i L l  n o t  c e l l  r h e s e  d e . . r e a s e s  t a d e p t i v e t .
R a t h e r .  I  a m  i n c l i n e d  t o  r e s t r i c t  t h i s  t e r n  t o  t h e  c a s e  w h e r e  L h e  u n -
d e r I e d  a n i r n a l  s p e n d s  I c s s  f r e e  e n e r g y  o n . r  g i v e n  I u n c t i o n  ( e . g .  p r o L e i n
E u r n o v e r ,  o r  m u s c u l a r  e f f o r t  f o r  a  g i v e n  b e h a v i o u r )  t h a n  a n  a d  l i b i c u m
f  ed  conspec i f  i c  t -  L i t e  se t l v  r t t : t g i 1 |  and  body  , - , c rT i r t r s r l  l . i ' r r r  wou ld  do  (p .71 ) .
I f  t h i s  p h e n o m e n o n  c o u l d  b e  s h o \ r n  t o  e x i s t ,  a  b a s i s  w o u l d  t h e r e b y  b e
l a i d  f o r  t h e  v i e w  t h a t  e v o l u t i o n  h a s  p r o v i d e d  t h e  i n d i v i d u a l  w i t h  a
^ - ^  - :  ^ 1  ^ ^ . . ^ L :  r :  + "  r f  e k i  n s  o u t  i  t s  n r o v i s i o n s  i n  o r d e r  L o  i n c r e a s e  L h eL d P a u ,  r l L y  u r  l L J  t s l u
c h a n c e  L h a t  i t  m a y  t i d e  o v e r  t e m p o r c r y  t o o d  s c e r c i r y ,  a  c o n d i t i o n
x_.
" T h i s  d i s c u s s i o n  e m p h a s i s e s  t i r e  c a s e  o f  u n d e r f e e d i n g ,  s i n c e  t h i s  i s  t h e
o n l y  c o n d i t i o n  u s e d  i n  m y  e x p e r i m e n t s .  A n  a n a l o g o u s  d e f i n i t i o n  o f ' a -
d a p t a t i o n  o f  e x p e n d i t u r e  t o  u p t a k e '  c a n  b e  f o r m u l a t e d  f o r  t h e  c a s e  o f
o v e r f e e d i n e .
co f i non  i n  t he  na tu ra l hab i t a t  o f  many  spec ies .  Howeve r ,  such  a  de f i n i -
t i o n  o f  a d a p t i v e  r e s ! r i c t i o n  o f  e x p e n d i t u r e  i n v o l v e s  f o r m i d a b l e  o p e r a -
t i o n a l  d i f f i c u l t i e s .  I  s h a 1 l  r e E u r n  t o  s o m e  a s p e c t s  o f  t h i s  p r o b l e m s  i n
c h a p t e r  8 .  F o r  t h e  m o m e n t  i t  w i l l  s u f f i c e  t o  s t a t e  t h a t  c o n c l u s i o n s  i n
t he  t i ce ra tu re  a re  no t  unan imous  as  t o  r he  ques t i on  whe the r  o r  no t
c h a n g e s  i n  m e t a b o l i s m  c a u s e d  b y  m a n i p u l a t i o n  o f  f o o d  i n L a k e ,  c a n  b e
a c c o u n t e d  f o r  e x c l u s i v e l y  i n  t e r m s  o f  c h a n g e d  b o d y  m a s s  a n d  c e s s a t i o n
o f  f o o d  p r o c e s s i n g .  C u m m i n g  a n d  M o r r i s o n  ( 1 9 6 0 )  s t a t e :  ' T h e  t o t a l  e n e r -
g y  e x p e n d i r u r e  o . [  L h e  r a t s  I e 1 I  d u r i n g  t h e  4 B  h r  f a s t  a n d  r o s e  d u r i n g
re feed ing .  L t r en  t he  changes  i n  body  we ighc  and  f ood  i n t ake  we re  a l l owed
fo r ,  t he  me tabo l i c  r a te  was  f ound  t o  r ema in  cons tan t  t h roughou t  t he
w h o l e  e x p e r i r n e n t a l  p e r i o d t ,  I n  c o n t r a s t ,  W a l k e r  a n d  G a r r e t t  ( 1 - o 7 0 )
c o n c l u d e  t h a t  e v e n  a f t e r  c o r r e c t i o n  f o r  b o d y  s i z e  r e d u c t i o n ' t h e  e n e r g y
expend i t u re  dec l i ned  marked l y  as  t he  pe r i od  o f  unde rnu t r i t i on  was  p ro -
l o n g e d ' .  ( T h e y  d i d  n o t  t a k e  i n t o  a c c o u n t  c h a n g e d  c o s t s  o f  f o o d  p r o c e s -
s i n g ,  b u t  E h i s  e f f e c c  w i l l  b e  c o r ) . s t a n t  f r o m  a b o u t  t h e  s e c o n d  d a y  o n -
n a r d s ,  w h e r e a s  t h e  d e c r e a s e  c o n t i n u e d  b e y o n d  t h a t  t i m e , )
T h e  p r e s e n t  s E u d y  i s  a  c o n t r i b u t i o n  t o  t h e  f u r t h e r  a n a l y s i s  o f
t h e  p r o b l e r n  o f  a d a p t a t i o n  o f  e n e r g y  e x p e n d i t u r e  t o  u p E a k e .  C l e a r l y ,
t h i s  c a n  n o t  b e  s o l v e d  b y  t h e  s t u d y  o f  t o t a l  m e t a b o l i c  r a l e  a l o n e ,  b u t
on l y  by  an  ana l ys i s  o f  t he  va r i ous  componen ts  l ha t  make  up  t h i s  t o t a l .
C u s t o m a r i l y  f o u r  c o m p o n e n t s  a r e  d i s t i n g u i s h e d  i n  t h e  e n e r g y  r n e t a b o l i s m
o f  a  h o m e o t h e r m  ( G e s s a m a n ,  1 9 7 3 ) :  b a s a l  m e t a b o l i s m ;  m e t a b o l i s m  a b o v e
t h e  b a s a l  l e v e l  w h i c h  i s  u s e d  f o r  t h e r m o r e g u l a t i o n ;  m e t a b o l i s m  a s s o c i a -
t e d  w i t h  a c t i v i t ' 1 ;  a n d  m e t a b o l i c  p r o c e s s e s  i n v o l v e d  i n  t h e  d i g e s t i o n  o f
f o o d .  I  s h a l l  u s e  t h e  s a m e  d i v i s i o n .  H o w e v e r ,  i t  s h o u l d  b e  p o i n r e d  o u t
t ha t  wha t  I  can  rneasu re  i n  my  expe r imen ts  i s  no t  t he  ra te  o f  ene rgy
e x p e n d i t u r e  e . g .  o n  t h e  p r o c e s s  o f  p e r f o r m i n g  m u s c u l a r  a c t i v i E y ,  b u t
on l y  t he  d i f f e rence  i n  meuabo l i c  r a te  be tween  t he  pe r i od  du r i ng  wh i ch
tha t  ac t i v i t y  t akes  p l ace  and  pe r i ods  i n  wh i ch  t he  an ima l  i s  no t  en -
g a g e d  i n  m u s c u l a r  a c E i v i t y .  T h i s  d i f f e r e n c e  g i v e s  r h e  c o s t  o f  a c r i v i r y
on l y  i f  t he  o the r  componen ts  o f  ene rgy  expend i t u re  ( d i ges t i on  and  o the r
p r o c e s s e s  i n  r e s L i n g  m u r a b o i i s m )  p r o c c e d  a t  r l r e  s J m e  r a L c  i r r e s p e c L i v e
o f  t h e  o c c u r r e n c e  o f  r n u s c u l a r  a c t i v i t y .  T  h a v e  n o  m e a n s  o f  a s c e r t a i n i n g
w h e t h e r  t h i s . i s  : ; o ,  b u t  i t  s e e m s  l r i g h l v  d o u h t f u l  f o r  i n s t a n c e  i n  v i e w
n L  I h e  e f f e ,  t s  o I  s y m p a t h e r i . '  d i s c l r a r g e  a n d  e J r e n o m e d u l  l a r y  s e c r e t i o n
c a u s i n g  s p l a n c h n i c  v a s c u l a r  c o n s t r i c t i o n ,  i n l r i b i t i o n  o f  l i p o g e n e s i s ,
e t c .  I n  p r i n c i p l e  t h e r t f o r e  I  c e n  s t . r t e  o n l - v  t h e  d i f f e r e n c e  i n  m e t a b o -
l i c  r : a t e  b e t w e e n  t h e  f  o L l o \ ^ / i n g  , ' . ) / r r 1 1 .  f . i : r t t s : .  l )  a n i m a l  r e s t i n g  i n  t h e  p o s t
; r b s o r p t i v e  s L a t c ,  2 )  e n i m a l  r e s r i n g  r n d  p r o (  e s s i n g  f o o d .  3 )  a n i m a l  a c -
t i v e .  F o r  b r e v i t y ,  h o w e v e r ,  I  s h a l l  d i s c u s s  m _ v  r e s u l t s  i n  t e r m s  o f  a
r e s t i n g ,  a  f o o d  p r o c e s s i n g ,  s n d  - - L n  e c t i v i t y  , z o n r t ' t '  ) t ' +  c r f  m e t a b o l i s m  (
( s e e  a l s o  p . 6 5 ) .  T h e  p o s s i b l e  i n f l u e n c e  o f  L h e  d e m a n d s  o f  t h e r m o r e g u l a -
t i o n  o n  m e t a b o l i c  r a L c  c o u l d  b e  s t u d i e d  i n  p r i n c i p l . ' b y  m a k i n g  o b s e r -
v a t i o n s  a f  d i f f e r e n t  a m b i e n t  t e m p e r i r t u r e s .  F o r  i n s t a n c e  i f  t h e  a n i m a l
i s  p l a c e d  i n  t h e  c o l d ,  t h i s  s h o u l d  l e a d  t o  a n  i n c r e a s e  i n  o n e  o r  m o r e
o f  t h e  o L h e r  L l r r e e  c o m l ) o n e n t s  o f  m c t l b o l i s m .  S u e l r  r e m p e r d t u r e  c x p e r i -
m e n L s ,  h o w e v e r ,  f e l l  o u t s i d e  t h e  s t ' o p e  o I  t h e  p r e s e n t  s t u d y .
T h e  l a b o r a t o r y  r e t  w a s  c h o s e n  a s  t h e  s r r h . i e c t  o f  m v  e x p e r i m e n t s  b e -
c a u s e  i t  i s  c o m m o n l y  u s e d  i n  s t u d i e s  o n  c a l t r r i c  r e g u l a c i o n .  I n t a k e  w a s
c h a n p e d  i n  o n e  d i  r e c t  i , r n  n n l v  n A h p l v  r e d r r c f i o n -  A l  I  e r n c r i m e n t s  w e r eJ  t  r r s i ' r \
d o n e  a t  t h e  s a m e  t e m p e r a t u r e  i n  t h e  t h e r m o n e u t r a l  z o n e  o f  f h e  r a t s  f o r
E w o  r e a s o n s ,  F i r s E ,  I  w i s h e d  ! o  a v c i d  t h e  c o n r p l i c a t i o n  o f  s p e c i a l  ( a n d
n o t  d i r e c t l y  m e a s u r a b l e )  h e a t  p r o d u c t i o n  f o r  t h e r m o r e g u l a t i o n .  S e c o n d ,
e x p e r i m e n t s  w i t h  f o o d  d e p r i v e d  a n i m a l s  c a n  b o  c o n t i n u e d  l o n g e r  w i  t h o u t
l p f h a l  p f I p c t s -  f o r  a L  t e m n e r a t u r ( , s  i n  o r  n e a r  l l r e  L h e r m r . n e u t r a l  z o D e
a n i m a l s  c a n  r n o b i l i z e  m o r e  o f  t h e i r  e n e r g y  s t u r e s  a s  s h o w n  b y  d a t a  o n
b i r d s  ( K e n d e i g h ,  1 9 4 5 )  a n d  r a t s  ( K l e i b e r ,  1 9 4 5 )  s t a r v e d  t i l l  d e a c h  a t
d i f f e r e n t  t e m p e r a t u r e s ,  C o n s e q u e n t l y  i n  m y  e x p e r i m e n t s ,  n o t w i t h s t a n d -
i n g  l o n g  p e r i o d s  o f  f o o d  d e p r i v a t i o n ,  o n l v  t w o  o u t  o f  m o r e  t h a n  o n e
h u n d r e d  a n i m a l s  d i e d :  t h e  o t h e r : s  c o u l d  b e  r e f e d .
T h e  e n e r g y  e x p e n d i t u r e  w a s  m c a s u r e d  b y  t w  m e t h o d s :  l )  a  b a l a n c e
t e c h n i q u e  ( c h a p t e r  3 ) ,  c a l c u l a t i n g  e x p e n d i t u r e  f r o m  f o o d  i n t a k e ,  f a e c e s
p r o d u c t i o n  a n d  c h a n g e s  i n  b o d y  r e s e r v e s ,  a n d  2 )  i n d i r e c L  c a l o r i m e t r y ,
c a l c u l a t i n g  e x p e n d i t u r e  f r o m  t h e  g a s  e x c h a n g c  o f  t h c  a n i m a l s  ( c h a p r e r s
t
4 -7 ) .  By  i nc reas ing  t he  t empo ra l  r eso lu t i on  o f  t he  l a t t e r  me thod  and
comb in i ng  i t  w i t h  o the r  r echn iques  a  de ta i l ed  ana l ys i s  o f  t oLa l  expen -
d i t u r e  i n t o  i t s  c o m p o n e n t s  w a s  m a d e  p o s s i b l e ,  T h i s  p r o c e c i u r e  w i l l  b e
d e s c r i b e d  i n  d e L a i l  i n  c h a p t e r  2 .
I  f i r s t  de te rm ined  t he  change  i n  t o t . a r  expend i t u re  du r i ng  f ood
dep r i va t i on  ( chap re r  3 ) ,  Th i s  change  \ ^ / as  f u r t he r  ana l ysed  i n  t e rms  o f
t h e  e n e r g e t i c  c o n s e q u e n c e s  o f :  l )  t h e  c e s s a E i o n  o f  f o o d  p r o c e s s i n g
( c h a p t e r  4 ) ; 2 )  c h a n g e s  o f  a c r i v i r y  ( c h a p t e r  5 ) ;  a n d  3 )  c h a n g e s  o f
f a s t i n g  r e s t i n g  m e t a b o l i c  r a t e  ( c h a p t e r  5 ) .  F i n a l l y  t h e  c o n s e q u e n c e s
o f  t he  expend i t u re  changes  f o r  r egu la t i on  o f  body  t empe ra tu re  we re
s t u d i e d  ( c h a p t e r  7 ) .  w i t h  r e s p e c t  t o  t h e  f i r s t  p o i n r  i u  i s  r e g r e t t a b l e
tha t  t he  ene rgy  expend i t u re  on  f eed ing  behav iou r  cou ld  no t  be  sepa ra -
red  f r om Lha t  on  o the r  behav iou r .  The re fo re  my  es t ima te  o f  t he  ene rgy
e x p e n d i t u r e  a s s o c i a r e d  w i t h  f o o d  p r o c e s s i n g  i n c l u d e d  o n l y  t h e  c o s t s  o f
i n t e rna l  p r : ocess ing ,  wh i l e  f o r  i ns tance  f ood  hand l i ng  was  measu red  t o -
ge the r  w i t h  t he  cos t s  o f  non - f eed ing  behav iou r .


   University of GroningenHow rats economizeWesterterp, Klaas RoelofIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:1976Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Westerterp, K. R. (1976). 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For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 30-10-2023CHAPTER IGENERAL INTRODUCTIONA d u l t  a n i r n a l s ,  l i v i n g  i n  a  c o n s t a n t  b i o l o g i c a l l y  a d e q u a t e  e n v i r o n m e n t ,ma in ta i n  a  ba lance  be tween  ene rgy  up take  and  ene rgv  expend i t u re .  Thee n e r g y  s t o r e  o f  t h e  b o d y  d o e s  n o t  f l u c t u a t e  m u c h ,  a s  t h e  c o n s t a n c y  o fbody  we igh t  and  body  compos i t i on  s t r ows ,  wh i l e  t he  s to re  i s  sma l l  i nc o m p a r i s o n  t o  t h e  d a i l y  e n e r g y  t u r n o v e r ,  e s p e c i a l l y  i n  s m a l l  a n i m a l s .T h i s  c a n  b e a c l . i e v e ' J  e i t h e r  b y  c o n t r o l  o f  t h e  u p t a k e  o r  t h e  e x p e n d i t u r eo f  e n e r g y .Tha t  an  an ima l  adap t s  i t s  up rake  t o  t he  expend i t u re  o f  ene rgy  i swe i l  known .  S tud ies  on  t h i s  po in t  we re  done  by  man ipu la t i ng  ene rgy  ex -pend i t u re  v i a  a  change  o f  env i r onmen ta l  t empe ra tu re  o r  v i a  t he  amoun to f  a c t i v i t y  i m p o s e d  o n  t h e  a n i m a l .  C o r t l e  a n d  C a r l s o n  ( 1 9 5 4 )  i n c r e a s e dt h e  e n e r g y  e x p e n d i t u r e  i n  r a E s  b y  l o w e r i n g  E h e  e n v i r o n m e n t a l  t e m p e r a -t u re  f r om 25o  C ,  a  va l ue  i n  o r  c l ose  t o  t he  t he rmoneuL ra l  zone  o f  t hese. - o ^an ima l s ,  t o  5 "  C .  An ima l s  p l aced  i n  t h i s  co l d  env i r onmen !  a te  tw i ce  asmuch  as  t he i r  con t ro l s  i n  t he  wa rm env i r onmen t .  Maye r  e t  a l .  ( 1954 )  ex -e r c i s e d  r a t s  i n  a  t r e a d m i l l  w i t h  a  s p e e d  o f  o n e  m i l e  p e r  h o u r .  T h e  a n i -ma l s  p rac t i ca l l y  doub led  t he i r  f ood  i n t ake  when  t he  du ra t i on  o f  exe r -c i se  was  i nc reased  f r om one  t o  s i x  hou rs  pe r  day ,  wh i l e  bod . v  we igh t  wasma in ta i ned .  The  measu red  changes  o f  f ood  i n t ake  we re  rep resen ta t i ve  f o re n c r g y  r . r p t a k e  b e c a u s e  i n  a d u l t  r a t s  i m p o r t a n t  c h a n g e s  o f  d i g e s r i o n  e f -f i c i ency  i n  r e l a t i on  t o  l he  l eve l  o f  f ood  i n t ake  a re  neve r  f ound( N e h r i n g  e t  a l . ,  1 9 5 9 ) .  I n  b o t h  e x p e r i m e n E s  m e n t i o n e d  a  b a l a n c e  b e t w e e nup take  and  expend i t u re  was  reached  aga in  unde r  t he  new  c i r cums tances  asshown  by  t he  cons tancy  o f  body  we igh t  du r i ng  more  t han  one  week .  Mo re -ove r ,  t he  s i ze  o f  t he  rese rves  was  p robab l y  no t  i - n f l uenced  because  t h i sbody  we igh t  had  t he  no rma l  va l ue .To  conc lude ,  an  an ima l  can  change  i t s  ene rgy  up t . ake  w i t h  a t  l eas ta  f ac to r  two  f o r  adap t i ng  i t  t o  t he  expend i t u re  o f  ene rgy .T h e  p o s s i b i L i t i r  t h a t  i t n  a n i m a l  a d a p t s  i t s  e x p e n d i c u r e  t o  t h e  u p -t a k e  o [  e n e r g y  i s  o f t e n  c a l l e d  i n  q u e s t i o n .  R e c e n L l y  L e  ] 4 a g n e n  ( 1 9 7 4 )c v c n  s L A L ( ' d  t l ) a t  L I ) e  (  L \ t ) t r r r l  d f  c n c r q y  o x p e n d i t u r e  i s  c ( , n L r ; r r y  t o  w h a Lb o d y  v i e i g h t  w o u l c i  r e q u i r e  i n  v i e w  o f  h y p e r a c t i v i t y  i n  f o o d  d e p r i v a t i o na n d  h y p o a c t i v i t y  i n  o b e s i t y .  l n v e s t i g a t i o n s  o n  t h i s  p o i n L  a v a i l a b L e  i nt h e  l i t e r a t u r e  i n v o l v e d  e i t h e r  p a r t i a l  ( K e y s  e t  a L . ,  1 9 5 0 ;  G r a n d e  e ti r 1 . ,  l 9 5 B ;  M e y e r  a n d  C l a w s o n ,  1 9 6 4 ;  l " l a l k t ' r  a n d  t l a r r e t t ,  I 9 7 0 ) ,  o r  L r o m -p l e t e  ( C u m n r i n g  a n d  M o r r i s o n ,  1 9 6 0 ;  K l e i b e r ,  l 9 6 l ;  l l o r r i s o n ,  l 9 6 B )  f o o dd e p r i v a L i o n  o r ,  o n l y  i n  m a n ,  r a i s i n g  o f  i n t a k e  b y  o v e r f e e d i n g  ( l { i 1 l e rc n d  l ' 4 u m I o r d ,  1 9 6 7 \ ,  I n  t l r e s c  e x p e r i r n c n L s ,  c o n L r . l r y  t r r  t h o s e  i n  w h i e  he x p e n d i t u r e  w a s  m a n i p u l a r e d ,  b o d y  w e i g h t  d i d  n o t  r e m a i n  a !  t h e  e q u i l i -b r i u m  1 e v e 1  f o r  a d  l i b i t u m  c o n d i t i o n s .  A  n e w  b a l a n c e  b e t w e e n  i n t a k e  a n de x p e n d i t u r e  w a s  r e a c h e d  o n l y  s o m e t i m e s  ( K e y s  e t  a 1 . ,  \ r l a l k e r  a n dG . 3 r r e t t ,  l . c ,  ) .  T l r e s e  f e c L s  c o m p l  i c a L e  t h e  i n L . " r p r e t i r I i o n  o t  L l ) c  r e -s u l t s  w i E h  r e s p e c t  t o  t h e  q u e s t  i . r n  o [  r : . :  '  :  . '  .  . r t .  i ' :  , r .  , . :  -l ; , i , t t s .  S o m e  m e t a b o l i c  s a v i n q s  w i l l  r e s u l t  f r o n  t h e  m e r e  f a c t  t h a t  t h e*u n d e r I e d  s u b j e c t " ' h a s  t o  h a n d l e  a n d  d i q e s t  l e s s  f o , r d  ] l r r r € o v € r ,  d u r i n gn ; t r l  i a l  r r r  c o n r r r l p l e  l  - - : " ^ r :  -  ' !  -  t  o l r r c , r o a n  . r n d  l e T  , r r  p r / o n  n l r t <r \  L r  u i H r  r  r ( u r r s  5 ! \ \ v F (o f  t h e  c e l  l s  t h e m s e l v e s  a r e  u s e d  a s  f u e l .  B o d y  m a s s  w i l  I  d e c r e a s e ,  a n dr h i s  i s  b o u n d  t o  c 3 u s e  d  d r o p  i r L  m e L a b o l i s m .  H o w e v e r ,  I o L l o w i n g  C u m m i n ga n d  l l o r r i s o n  ( 1 . c . ) ,  T  w i L l  n o t  c e l l  r h e s e  d e . . r e a s e s  t a d e p t i v e t .R a t h e r .  I  a m  i n c l i n e d  t o  r e s t r i c t  t h i s  t e r n  t o  t h e  c a s e  w h e r e  L h e  u n -d e r I e d  a n i r n a l  s p e n d s  I c s s  f r e e  e n e r g y  o n . r  g i v e n  I u n c t i o n  ( e . g .  p r o L e i nE u r n o v e r ,  o r  m u s c u l a r  e f f o r t  f o r  a  g i v e n  b e h a v i o u r )  t h a n  a n  a d  l i b i c u mf  ed  conspec i f  i c  t -  L i t e  se t l v  r t t : t g i 1 |  and  body  , - , c rT i r t r s r l  l . i ' r r r  wou ld  do  (p .71 ) .I f  t h i s  p h e n o m e n o n  c o u l d  b e  s h o \ r n  t o  e x i s t ,  a  b a s i s  w o u l d  t h e r e b y  b el a i d  f o r  t h e  v i e w  t h a t  e v o l u t i o n  h a s  p r o v i d e d  t h e  i n d i v i d u a l  w i t h  a^ - ^  - :  ^ 1  ^ ^ . . ^ L :  r :  + "  r f  e k i  n s  o u t  i  t s  n r o v i s i o n s  i n  o r d e r  L o  i n c r e a s e  L h eL d P a u ,  r l L y  u r  l L J  t s l uc h a n c e  L h a t  i t  m a y  t i d e  o v e r  t e m p o r c r y  t o o d  s c e r c i r y ,  a  c o n d i t i o nx_." T h i s  d i s c u s s i o n  e m p h a s i s e s  t i r e  c a s e  o f  u n d e r f e e d i n g ,  s i n c e  t h i s  i s  t h eo n l y  c o n d i t i o n  u s e d  i n  m y  e x p e r i m e n t s .  A n  a n a l o g o u s  d e f i n i t i o n  o f ' a -d a p t a t i o n  o f  e x p e n d i t u r e  t o  u p t a k e '  c a n  b e  f o r m u l a t e d  f o r  t h e  c a s e  o fo v e r f e e d i n e .co f i non  i n  t he  na tu ra l hab i t a t  o f  many  spec ies .  Howeve r ,  such  a  de f i n i -t i o n  o f  a d a p t i v e  r e s ! r i c t i o n  o f  e x p e n d i t u r e  i n v o l v e s  f o r m i d a b l e  o p e r a -t i o n a l  d i f f i c u l t i e s .  I  s h a 1 l  r e E u r n  t o  s o m e  a s p e c t s  o f  t h i s  p r o b l e m s  i nc h a p t e r  8 .  F o r  t h e  m o m e n t  i t  w i l l  s u f f i c e  t o  s t a t e  t h a t  c o n c l u s i o n s  i nt he  t i ce ra tu re  a re  no t  unan imous  as  t o  r he  ques t i on  whe the r  o r  no tc h a n g e s  i n  m e t a b o l i s m  c a u s e d  b y  m a n i p u l a t i o n  o f  f o o d  i n L a k e ,  c a n  b ea c c o u n t e d  f o r  e x c l u s i v e l y  i n  t e r m s  o f  c h a n g e d  b o d y  m a s s  a n d  c e s s a t i o no f  f o o d  p r o c e s s i n g .  C u m m i n g  a n d  M o r r i s o n  ( 1 9 6 0 )  s t a t e :  ' T h e  t o t a l  e n e r -g y  e x p e n d i r u r e  o . [  L h e  r a t s  I e 1 I  d u r i n g  t h e  4 B  h r  f a s t  a n d  r o s e  d u r i n gre feed ing .  L t r en  t he  changes  i n  body  we ighc  and  f ood  i n t ake  we re  a l l owedfo r ,  t he  me tabo l i c  r a te  was  f ound  t o  r ema in  cons tan t  t h roughou t  t hew h o l e  e x p e r i r n e n t a l  p e r i o d t ,  I n  c o n t r a s t ,  W a l k e r  a n d  G a r r e t t  ( 1 - o 7 0 )c o n c l u d e  t h a t  e v e n  a f t e r  c o r r e c t i o n  f o r  b o d y  s i z e  r e d u c t i o n ' t h e  e n e r g yexpend i t u re  dec l i ned  marked l y  as  t he  pe r i od  o f  unde rnu t r i t i on  was  p ro -l o n g e d ' .  ( T h e y  d i d  n o t  t a k e  i n t o  a c c o u n t  c h a n g e d  c o s t s  o f  f o o d  p r o c e s -s i n g ,  b u t  E h i s  e f f e c c  w i l l  b e  c o r ) . s t a n t  f r o m  a b o u t  t h e  s e c o n d  d a y  o n -n a r d s ,  w h e r e a s  t h e  d e c r e a s e  c o n t i n u e d  b e y o n d  t h a t  t i m e , )T h e  p r e s e n t  s E u d y  i s  a  c o n t r i b u t i o n  t o  t h e  f u r t h e r  a n a l y s i s  o ft h e  p r o b l e r n  o f  a d a p t a t i o n  o f  e n e r g y  e x p e n d i t u r e  t o  u p E a k e .  C l e a r l y ,t h i s  c a n  n o t  b e  s o l v e d  b y  t h e  s t u d y  o f  t o t a l  m e t a b o l i c  r a l e  a l o n e ,  b u ton l y  by  an  ana l ys i s  o f  t he  va r i ous  componen ts  l ha t  make  up  t h i s  t o t a l .C u s t o m a r i l y  f o u r  c o m p o n e n t s  a r e  d i s t i n g u i s h e d  i n  t h e  e n e r g y  r n e t a b o l i s mo f  a  h o m e o t h e r m  ( G e s s a m a n ,  1 9 7 3 ) :  b a s a l  m e t a b o l i s m ;  m e t a b o l i s m  a b o v et h e  b a s a l  l e v e l  w h i c h  i s  u s e d  f o r  t h e r m o r e g u l a t i o n ;  m e t a b o l i s m  a s s o c i a -t e d  w i t h  a c t i v i t ' 1 ;  a n d  m e t a b o l i c  p r o c e s s e s  i n v o l v e d  i n  t h e  d i g e s t i o n  o ff o o d .  I  s h a l l  u s e  t h e  s a m e  d i v i s i o n .  H o w e v e r ,  i t  s h o u l d  b e  p o i n r e d  o u tt ha t  wha t  I  can  rneasu re  i n  my  expe r imen ts  i s  no t  t he  ra te  o f  ene rgye x p e n d i t u r e  e . g .  o n  t h e  p r o c e s s  o f  p e r f o r m i n g  m u s c u l a r  a c t i v i E y ,  b u ton l y  t he  d i f f e rence  i n  meuabo l i c  r a te  be tween  t he  pe r i od  du r i ng  wh i chtha t  ac t i v i t y  t akes  p l ace  and  pe r i ods  i n  wh i ch  t he  an ima l  i s  no t  en -g a g e d  i n  m u s c u l a r  a c E i v i t y .  T h i s  d i f f e r e n c e  g i v e s  r h e  c o s t  o f  a c r i v i r yon l y  i f  t he  o the r  componen ts  o f  ene rgy  expend i t u re  ( d i ges t i on  and  o the rp r o c e s s e s  i n  r e s L i n g  m u r a b o i i s m )  p r o c c e d  a t  r l r e  s J m e  r a L c  i r r e s p e c L i v eo f  t h e  o c c u r r e n c e  o f  r n u s c u l a r  a c t i v i t y .  T  h a v e  n o  m e a n s  o f  a s c e r t a i n i n gw h e t h e r  t h i s . i s  : ; o ,  b u t  i t  s e e m s  l r i g h l v  d o u h t f u l  f o r  i n s t a n c e  i n  v i e wn L  I h e  e f f e ,  t s  o I  s y m p a t h e r i . '  d i s c l r a r g e  a n d  e J r e n o m e d u l  l a r y  s e c r e t i o nc a u s i n g  s p l a n c h n i c  v a s c u l a r  c o n s t r i c t i o n ,  i n l r i b i t i o n  o f  l i p o g e n e s i s ,e t c .  I n  p r i n c i p l e  t h e r t f o r e  I  c e n  s t . r t e  o n l - v  t h e  d i f f e r e n c e  i n  m e t a b o -l i c  r : a t e  b e t w e e n  t h e  f  o L l o \ ^ / i n g  , ' . ) / r r 1 1 .  f . i : r t t s : .  l )  a n i m a l  r e s t i n g  i n  t h e  p o s t; r b s o r p t i v e  s L a t c ,  2 )  e n i m a l  r e s r i n g  r n d  p r o (  e s s i n g  f o o d .  3 )  a n i m a l  a c -t i v e .  F o r  b r e v i t y ,  h o w e v e r ,  I  s h a l l  d i s c u s s  m _ v  r e s u l t s  i n  t e r m s  o f  ar e s t i n g ,  a  f o o d  p r o c e s s i n g ,  s n d  - - L n  e c t i v i t y  , z o n r t ' t '  ) t ' +  c r f  m e t a b o l i s m  (( s e e  a l s o  p . 6 5 ) .  T h e  p o s s i b l e  i n f l u e n c e  o f  L h e  d e m a n d s  o f  t h e r m o r e g u l a -t i o n  o n  m e t a b o l i c  r a L c  c o u l d  b e  s t u d i e d  i n  p r i n c i p l . ' b y  m a k i n g  o b s e r -v a t i o n s  a f  d i f f e r e n t  a m b i e n t  t e m p e r i r t u r e s .  F o r  i n s t a n c e  i f  t h e  a n i m a li s  p l a c e d  i n  t h e  c o l d ,  t h i s  s h o u l d  l e a d  t o  a n  i n c r e a s e  i n  o n e  o r  m o r eo f  t h e  o L h e r  L l r r e e  c o m l ) o n e n t s  o f  m c t l b o l i s m .  S u e l r  r e m p e r d t u r e  c x p e r i -m e n L s ,  h o w e v e r ,  f e l l  o u t s i d e  t h e  s t ' o p e  o I  t h e  p r e s e n t  s t u d y .T h e  l a b o r a t o r y  r e t  w a s  c h o s e n  a s  t h e  s r r h . i e c t  o f  m v  e x p e r i m e n t s  b e -c a u s e  i t  i s  c o m m o n l y  u s e d  i n  s t u d i e s  o n  c a l t r r i c  r e g u l a c i o n .  I n t a k e  w a sc h a n p e d  i n  o n e  d i  r e c t  i , r n  n n l v  n A h p l v  r e d r r c f i o n -  A l  I  e r n c r i m e n t s  w e r eJ  t  r r s i ' r \d o n e  a t  t h e  s a m e  t e m p e r a t u r e  i n  t h e  t h e r m o n e u t r a l  z o n e  o f  f h e  r a t s  f o rE w o  r e a s o n s ,  F i r s E ,  I  w i s h e d  ! o  a v c i d  t h e  c o n r p l i c a t i o n  o f  s p e c i a l  ( a n dn o t  d i r e c t l y  m e a s u r a b l e )  h e a t  p r o d u c t i o n  f o r  t h e r m o r e g u l a t i o n .  S e c o n d ,e x p e r i m e n t s  w i t h  f o o d  d e p r i v e d  a n i m a l s  c a n  b o  c o n t i n u e d  l o n g e r  w i  t h o u tl p f h a l  p f I p c t s -  f o r  a L  t e m n e r a t u r ( , s  i n  o r  n e a r  l l r e  L h e r m r . n e u t r a l  z o D ea n i m a l s  c a n  r n o b i l i z e  m o r e  o f  t h e i r  e n e r g y  s t u r e s  a s  s h o w n  b y  d a t a  o nb i r d s  ( K e n d e i g h ,  1 9 4 5 )  a n d  r a t s  ( K l e i b e r ,  1 9 4 5 )  s t a r v e d  t i l l  d e a c h  a td i f f e r e n t  t e m p e r a t u r e s ,  C o n s e q u e n t l y  i n  m y  e x p e r i m e n t s ,  n o t w i t h s t a n d -i n g  l o n g  p e r i o d s  o f  f o o d  d e p r i v a t i o n ,  o n l v  t w o  o u t  o f  m o r e  t h a n  o n eh u n d r e d  a n i m a l s  d i e d :  t h e  o t h e r : s  c o u l d  b e  r e f e d .T h e  e n e r g y  e x p e n d i t u r e  w a s  m c a s u r e d  b y  t w  m e t h o d s :  l )  a  b a l a n c et e c h n i q u e  ( c h a p t e r  3 ) ,  c a l c u l a t i n g  e x p e n d i t u r e  f r o m  f o o d  i n t a k e ,  f a e c e sp r o d u c t i o n  a n d  c h a n g e s  i n  b o d y  r e s e r v e s ,  a n d  2 )  i n d i r e c L  c a l o r i m e t r y ,c a l c u l a t i n g  e x p e n d i t u r e  f r o m  t h e  g a s  e x c h a n g c  o f  t h c  a n i m a l s  ( c h a p r e r st4 -7 ) .  By  i nc reas ing  t he  t empo ra l  r eso lu t i on  o f  t he  l a t t e r  me thod  andcomb in i ng  i t  w i t h  o the r  r echn iques  a  de ta i l ed  ana l ys i s  o f  t oLa l  expen -d i t u r e  i n t o  i t s  c o m p o n e n t s  w a s  m a d e  p o s s i b l e ,  T h i s  p r o c e c i u r e  w i l l  b ed e s c r i b e d  i n  d e L a i l  i n  c h a p t e r  2 .I  f i r s t  de te rm ined  t he  change  i n  t o t . a r  expend i t u re  du r i ng  f ooddep r i va t i on  ( chap re r  3 ) ,  Th i s  change  \ ^ / as  f u r t he r  ana l ysed  i n  t e rms  o ft h e  e n e r g e t i c  c o n s e q u e n c e s  o f :  l )  t h e  c e s s a E i o n  o f  f o o d  p r o c e s s i n g( c h a p t e r  4 ) ; 2 )  c h a n g e s  o f  a c r i v i r y  ( c h a p t e r  5 ) ;  a n d  3 )  c h a n g e s  o ff a s t i n g  r e s t i n g  m e t a b o l i c  r a t e  ( c h a p t e r  5 ) .  F i n a l l y  t h e  c o n s e q u e n c e so f  t he  expend i t u re  changes  f o r  r egu la t i on  o f  body  t empe ra tu re  we res t u d i e d  ( c h a p t e r  7 ) .  w i t h  r e s p e c t  t o  t h e  f i r s t  p o i n r  i u  i s  r e g r e t t a b l etha t  t he  ene rgy  expend i t u re  on  f eed ing  behav iou r  cou ld  no t  be  sepa ra -red  f r om Lha t  on  o the r  behav iou r .  The re fo re  my  es t ima te  o f  t he  ene rgye x p e n d i t u r e  a s s o c i a r e d  w i t h  f o o d  p r o c e s s i n g  i n c l u d e d  o n l y  t h e  c o s t s  o fi n t e rna l  p r : ocess ing ,  wh i l e  f o r  i ns tance  f ood  hand l i ng  was  measu red  t o -ge the r  w i t h  t he  cos t s  o f  non - f eed ing  behav iou r .

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How rats economize:Energy loss in starvation

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