The influence of exercise on serum enzyme levels in the horse.

A group of clinically normal horses was subjected to controlled strenuous exercise. Elevated serum concentrations of lactic dehydrogenase, aldolase and creatine kinase were observed after exercise but no significant change in serum glutamic-oxalacetic transaminase was noted. These changes were reduced by repeated exposure to exercise suggesting that measurement of serum enzyme elevations, particularly creatine kinase, might be a useful index of fitness in the horse. Administration of prednisolone prior to exercise also reduced these changes. Since the serum enzyme concentrations had returned to normal within 72 hours of exercise, and since the cytoplasmic enzyme glutamic oxalacetic transaminase was not released from the tissues this supported the hypothesis that efflux of intracellular enzymes into the circulation was due to a temporary selective change in cell membrane permeability rather than to tissue necrosis.