Myocardial dysfunction in diabetic rats: influence of beta-adrenoceptor blockade (propranolol)

The effects of a beta-blocker, propranolol, on the enzyme and isoenzyme activities in the heart muscle in vitro and concomitant histopathology of the component cells of the islets of Langerhans were studied in the Wistar rats after treatment with streptozotocin and isoproterenol. The biochemical data indicated that the isoproterenol induced myocardial infarction (MI) precipitates an acute diabetic response in the rat heart. The superimposition of MI in diabetes mellitus caused significant inhibition of phosphofructokinase and hexokinase in the heart muscle. The lactate dehydrogenase depicted shifting of H-type to M-type in diabetes with or without MI. The drugs, when administered in combination, brought distinctive histopathological changes in beta-cells of the pancreatic islets including degranulation, hyalinosis and a near-total destruction; however A and D cells remained more or less unaffected. The effect of propranolol in diabetes mellitus was uncertain but in MI with or without prior diabetes, the drug inversely altered the activities of all the cardiac enzymes, besides stimulating a mild recuperation of the cells of the endocrine parenchyma.