Acid hydrolase activities in mouse cardiac and skeletal muscle following exhaustive exercise.

Acid hydrolase activities in skeletal and cardiac muscle were studied 5, 10 and 20 days after exhaustive intermittent running by untrained and endurance-trained mice. Exhaustion increased the activities of cathepsin D, beta-glucuronidase and ribonuclease, but not that of p-nitrophenylphosphatase in skeletal muscle of untrained mice. Activities were highest on the fifth day after exhaustion and decreased during the following two weeks. More intensive loading produced no changes in acid hydrolytic capacity in skeletal muscle of endurance-trained mice. Acid hydrolase activities in cardiac muscle of both untrained and trained mice were unaffected by exhaustive running. It is suggested that exhaustive running causes both lethal and sublethal hypoxic fiber injuries in the skeletal muscle of untrained mice but not in that of endurance-trained mice or in the cardiac muscle of animals of either group. These injuries manifest themselves as fiber necrosis (lethal) and as increased acid hydrolytic capacity in surviving fibers (sublethal).