The effect of continuous removal of thoracic duct lymph on plasma activities
of creatine phosphokinase (PCK), glutamic-oxaloacetic transaminase (PAST); and lactic
dehydrogenase (PLDH), was examined in pentobarbital-anaesthetised dogs over a 5.5-
hour period. PCK and PAST declined relative to levels in control dogs while PLDH was
unaltered. Lymph/plasma (L/P) ratios for AST and CPK were greater, and for LDH less,
than the L/P ratio for total protein. It was concluded that PCK, and to some extent PAST,
are normally maintained by introduction of enzyme, escaping from the intracellular
compartment, into the circulating blood via the lymphatic system. PLDH and PAST
appear to be maintained principally by introduction of enzyme directly from the intracellular
to the plasma compartment.