CORRELATION BETWEEN MYOCARDIAL DYSFUNCTION AND CHANGES IN MYOSIN ISOENZYMES IN DIABETIC RAT HEARTS

We investigated the relationship between papillary muscle function and the myosin isoenzyme pattern, collagen content, and the type of myoca rdial collagen in diabetic rats to elucidate the mechanism of short-te rm myocardial dysfunction in diabetes. Diabetes was induced in 9-week- oId male Wistar rats with a single intravenous injection of streptozot ocin. One-half of the diabetic rats were treated with insulin. Age-mat ched control rats were also studied. The time to peak tension (TPT) of isometric papillary muscle contraction, time to 1/2 relaxation, and t ime from the peak tension to the peak decrease in tension (TPN) were s ignificantly prolonged in diabetic rats at 4, 8, and 12 weeks. The pea k increase and decrease in tension were slower in the diabetic rats co mpared with control rats. The level of the myocardial myosin isoenzyme V3 was greater in diabetic rats than in control rats at each interval . Findings in insulin-treated rats were similar to those in controls. The collagen content and the ratio of type I collagen to type III coll agen were similar in all groups. The V3 level was significantly correl ated with mechanical parameters (TPT versus %V3: r = 0.81, p < 0.01; T PN versus %V3: r = 0.78, p < 0.01). Our findings suggest that short-te rm myocardial dysfunction in diabetic rats is related to changes in th e myosin isoenzyme pattern.