The work described in this thesis involved a
study of isoenzymes (multiple forms of enzymes arising
from genetically determined differences in primary
structure) in ovine tissues and serum. The study
is divided into three major parts.The first part describes the technical problems
encountered and the methods used to solve these
problems in relation to separating the isoenzymes of
lactate dehydrogenase, glucosephosphate isomerase,
aldolase, aspartate aminotransferase and creatine
kinase. Both isoelectric focusing and electrophoresis
were investigated but only the latter proved suitable
for the quantitative estimations described in parts
two and three.In the second part, normal isoenzyme levels were
established in ovine tissues and an extensive
investigation, involving 151 sheep, was carried out to
determine the effect of physiological parameters on
serum isoenzyme levels. Time after parturition in
ewes and age in lambs affected serum lactate dehydro¬
genase isoenzyme levels but sex and growth rate
produced no effects of any clinical significance. In
a separate experiment, the frequency and mode of
inheritance of two genetic variants of glucosephosphate isomerase was investigated.In the third part, the serum and tissue levels
of lactate dehydrogenase and creatine kinase were
studied in respiratory and gastrointestinal tract
disease. In chronic proliferative exudative
pneumonia and in acute pasteurella pneumonia, no
changes in serum isoenzyme levels were observed which
were likely to be of diagnostic value, despite a
marked increase in the total lactate dehydrogenase
level and changes in the distribution of its isoenzymes
in pneumonic lungs. In chronic gastrointestinal
parasitism, changes in serum lactate dehydrogenase and
creatine kinase isoenzyme levels attributable to
damage to the intestinal tract caused by Trichostrongylus vitrinus were detectable and may be of value
in following the course of experimental infections in
the live sheep. In the acute and chronic stages of
parasitic gastritis caused by Ostertagia circumcincta
or Ha emonchus contortus, no diagnostically useful
serum isoenzyme changes were observed. In acute
ID. circumcincta infection, isoenzyme levels in serum,
and lymph from the gastric lymph duct were measured.
Lymph isoenzymes were no more sensitive than serum
isoenzymes in detecting damage to the abomasal mucosa,
suggesting that the isoenzymes may have been released
from the mucosa into the lumen of the abomasum rather
than into the circulation via the lymphatic drainageChanges in the lactate dehydrogenase isoenzyme
distribution of the abomasal mucosa were observed in
acute parasitic gastritis but these were not reflected
in the serum isoenzyme levels
