EXERCISE ALTERS CARDIAC MYOSIN ISOZYME DISTRIBUTION IN OBESE ZUCKER AND WISTAR RATS

Recent evidence suggests that exercise training may significantly increase the expression of the cardiac myosin isozyme V1 in the diabetic heart, a change associated with improved cardiac functional capacity. To test this hypothesis, cardiac myofibrillar adenosinetriphosphatase (ATPase) activity and myosin isozyme profiles were determined in trained and sedentary male hyperinsulinemic obese Zucker (OZT, OZS) and obese Wistar (OWT, OWS) rats. Lean sedentary (LZS, LWS) animals served as age-matched controls. Myofibrillar ATPase activity and the relative quantity of the high-ATPase isozyme V1 was significantly lower in both strains of sedentary obese rats than in the respective lean sedentary controls (P < 0.05). Both 5 (OZT) and 10 wk (OWT) of moderate treadmill training increased these markers of cardiac myosin biochemistry in the obese animals (P < 0.05). Thus, endurance exercise training remodels the cardiac isomyosin profile of hyperinsulinemic rats and in doing so, may enhance cardiac contractility and functional capacity. Such changes may reflect an improvement in glucose availability and utilization in these hearts.