Resistance of diabetic rat hearts to Ca overload-related injury. Histochemical and ultrastructural study.

The enzymatic histochemical and ultrastructural alterations of the rat heart during development of streptozotocin (STZ) induced diabetic cardiomyopathy were studied. Moreover, the response of the isolated diabetic hearts to Ca overload-Ca paradox-was investigated. In the early stage of diabetes (1 week of diabetes), no apparent histochemical changes were observed but gentle alterations of the ultrastructure of the myocytes and particularly capillaries were found. Structural changes of the myocytes and microangiopathy accompanied by decreased activities of some enzymes (phosphorylase, various dehydrogenases, ATPase) progressed with time and were more pronounced late in diabetes (9 weeks). Ca paradox induced severe structural damage of the majority of cardiomyocytes and loss of the cellular integrity, and marked decrease in activities of all enzymes. However, in acute diabetic heart only partial Ca paradox was observed. It was manifested by transmural heterogeneity of structural and enzymatic histochemical changes. Evident preservation of the ultrastructure and enzyme activities of the myocardium was revealed in late stage (9 weeks) of diabetes. It can be concluded that diabetes results in prevention of the Ca overload in rat myocardium in vitro. Disturbances in coronary perfusion associated with microangiopathy as well as altered Ca handling and depressed heart function may account for delayed development of Ca paradox in diabetic heart.