Changes in cardiac lactate dehydrogenase isoenzymes following experimental necrosis in rats

Following a subcutaneous injection of isoproterenol (ISO) into adult rats (30 mg/100 g, B.W.), the cardiac total lactate dehydrogenase (LDH) activity was decreased by about 53.81% in less than 24 H. Restoration of myocardial LDH activity was seen at 24 H and 48 H. LDH-I activity exceeded LDH-V in the control heart, while LDH-I, LDH-II and LDH-III decreased at 48 H following ISO injection. These changes were associated with concomitant elevation in LDH-V activity. Percentage M-LDH was less than H-LDH till 12 H in the necrotic heart muscle but exceeded the latter at 24H and 48 H. Similar changes were marked in absolute H-LDH and M-LDH activities when compared with the total LDH activity. Histopathological studies revealed and confirmed the occurrence of infarcts. The results indicate the potential of myocardial tissue for efficient shifting of H-LDH synthesis to M-LDH synthesis in the necrotic heart.