Changes in the Activities of Lysosomal Enzymes in Infarcted Canine Heart Muscle

Experimental myocardial infarction was produced in 32 mongrel dogs. The changes in activity of four lysosomal enzymes (acid phosphatase, glucuronidase, deoxyribonuclease, and γ-glutamyl-transpeptidase) were examined in the soluble and the particle-bound fraction. The pattern of changes in free and particle-bound enzyme activity observed was similar for all four enzymes. During the first 48 hours after coronary occlusion, the particle-bound enzyme activity was decreased, while the free activity was moderately increased, reflecting the autolytic phase of cell and tissue destruction. Between the second and the sixth day, the soluble hydrolytic enzyme activity was maximal and the particle-bound activity was slowly increasing. During this period, the main part of tissue degradation and removal of cell debris takes place. Ten days after myocardial infarction the free hydrolytic activity had returned to control values, but the particle-bound enzyme activity was four to ten times higher in the infarcted tissue than in the control muscle.