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.