Insulin reversal of biochemical changes in hearts from diabetic rats

Reversal of myocardial biochemical changes with insulin treatment (4 and 8 wk) was studied in 8 and 12 wk streptozotocin (STZ)-diabetic rats. STZ-induced diabetes was characterized by elevations in blood glucose, serum cholesterol, and triglycerides and depressed serum insulin levels. Insulin treatment for 4 and 8 wk completely restored the serum alterations to control values. The polyuria, polydipsia, and polyphagia were also markedly diminished by the insulin treatment. Diabetic rats had pronounced decreases in body, heart, and left ventricular weights, all of which were completely reversed by the insulin treatment. Hydroxyproline accumulation in diabetic rat hearts was only reversed by the 8-wk and not by the 4-wk insulin treatment. STZ produced a significant depletion of left ventricular magnesium content as well as depression of K+-stimulated sarcoplasmic reticulum and myofibrillar ATPase activities. Both the 4- and 8-wk insulin treatment produced a complete recovery of the myocardial magnesium content. No significant changes in sarcolemmal Na+-K+-ATPase and K+-stimulated p-nitrophenyl phosphatase activities were observed in diabetic animals compared with control. The decreased latency of the lysosomal hydrolase, N-acetyl-beta-glucosaminidase, and the increased collagen deposition observed in the diabetic hearts were only partially reversed by the 4-wk insulin treatment, but completely reversed by the 8-wk treatment period.