Cardiac cell damage: a primary myocardial disease in streptozotocin-induced chronic diabetes.

Ultrastructural changes in heart muscle due to chronic diabetes subsequent to a single injection of streptozotocin (65 mg/kg body wt, i.v.) were studied in rats. Presence of diabetes was indicated by hyperglycaemia (plasma glucose, control, 120 +/- 7; diabetic, 448 +/- 21 mg/dl) as well as hypo-insulinaemia (plasma insulin, control, 25.6 +/- 5.2; diabetic, 11.2 +/- 0.5 microU/ml). After 8 weeks of diabetes, the hearts were processed for electron microscopic examination. Cardiac muscle cells in diabetic hearts showed condensation of nuclear chromatin and folding of nuclear membranes. Swelling of mitochondria, clearing of mitochondrial matrix and incorporation of lysosomal membranes into mitochondrial matrix was also noted. A marked increase in both lysosomes and lipid droplets was apparent. Focal areas in diabetic hearts showed contracted sarcomeres, myofibrillar degeneration and separation of the intercalated disc. Atherosclerotic plaque formation as well as structural changes in the smooth muscle or endothelial cells in the small arteries, arterioles or capillaries were not seen to accompany the structural changes in the cardiac muscle cells of the diabetic hearts. This study provides strong evidence for the occurrence of primary myocardial disease in streptozotocin-induced chronic diabetes.