Cardiac ultrastructural changes in streptozotocin-induced diabetic rats: effects of insulin treatment

The effect of insulin treatment on myocardial ultrastructure was studied in experimentally induced diabetic male rats. Rats received an intravenous injection of 60 mg/kg streptozotocin and were tested for glycosuria 3 days later. Half of these animals were then given 3.0 U of protamine zinc insulin daily subcutaneously and again tested for glycosuria. The significant loss in weight observed in the untreated diabetics was prevented in the insulin-treated diabetics. Electron microscopic observation of the left ventricular myocardium from 3 month untreated diabetics revealed mild edema adjacent to the sarcoplasmic reticulum. A more severe form of edema, focal in nature, was also observed. Some distended mitochondria and disrupted banding were associated with these focal areas of edema. Increased lipid levels and intramitochondrial dense staining particles were found in the untreated diabetics. On the other hand, hearts from insulin-treated diabetics did not exhibit these alterations. They did, however, exhibit mitochondrial clumping which was also seen in the untreated diabetics and the same capillary changes. The latter involved a thickening of the lamina densa, loss of the lamina lucida and an increased number of micropinocytotic vesicles in the capillary walls. These results suggest that insulin treatment is capable of preventing only some of the ultrastructural changes induced by streptozotocin-diabetes in rat hearts.