Institutionen för kvinnors och barns hälsa / Department of Women's and Children's Health
Abstract
Ion transport in the gastrointestinal tract is vital for cellular
homeostasis and to ensure growth during ontogeny. We have therefore
investigated the regulation and maturation of sodium, potassium and
hydrogen transport in the gastrointestinal tract.
Net jejunal sodium absorption is significantly higher in young as
compared to adult rats. During high salt intake, net sodium absorption
decreases in young but not in adult rats. When dopamine production was
inhibited we did not observe decreased sodium absorption in young rats on
high salt diet. The reduced sodium absorption during high salt intake in
young rats requires endogenous dopamine action.
Net colonic potassium absorption in young rats is five times higher than
in adult ones. The majority of colonic net potassium absorption occurs in
the distal part of the colon. Using different approaches this study shows
that apically located transporters which reabsorb potassium are
upregulated in the infant rat while secreting basolateral transporters
are upregulated in adult rats. Infant rat H+, K+- ATPase and
ouabainsensitive sodium independent ATPase were higher but Na+, K+-ATPase
was lower than in the adult rat.
Angiotensin II induces potassium secretion in rat distal colon. This
effect is mediated through both receptors (AT1, and AT2) and by at least
three different pathways (Na+, K+, 2CIcotransporter, the apical
barium-sensitive potassium channels and the Na+, K+-ATPase).
Rat gastric H+, K+- ATPase matures postnatally. The expression of H+, K+-ATPase
increases from day 10. Gastric H+, K+- ATPase increased 2.5-fold when
10-day-old rats were treated with a single dose of glucocorticoids.
A study of human gastric H+, K+- ATPase enzyme was performed on biopsies
from neonates. The amount of H+, K- ATPase increases in relation to
gestational and postnatal age. Boys have a significantly higher amount
than girls. This is the first study on a large number of infants showing
that gastric H+, K+- ATPase is present before term birth and that it
increases during development.
Conclusion: In summary, these studies of ion transport in the
gastrointestinal tract show new mechanisms that ensure proper regulation
of sodium, potassium and hydrogen transport during development. We have
found that glucorticoids and dopamine have specific actions on ion
transport during early development. In addition we have found that
angiotensin II regulates colonic potassium transport in a complex manner
