The effect of sulfonylurea therapy on defective calcium movement associated with diabetic cardiomyopathy

Adult rats exposed to 70 mg/kg streptozocin developed characteristic symptoms of overt diabetes, such as muscle wasting and severely elevated blood glucose levels. Chronic treatment of these rats with the sulfonylurea glyburide for a period of 5 weeks did not affect either the weight of the animal or the degree of hyperglycemia. The drug also failed to influence myocardial glucose metabolism. Nevertheless, the decline in myocardial function associated with the diabetic cardiomyopathy was less in the glyburide-treated rats. At higher preload, myocardial work was significantly reduced in the untreated diabetic but was only moderately depressed in the glyburide-treated heart relative to the nondiabetic heart. The improvement in mechanical function was associated with partial recovery of sarcolemmal calcium pump activity. The drug did not alter the initial rateof Na⁺-Ca²⁺ exchange, but decreased the capacity of the transport system. The results indicate that glyburide benefits the diabetic heart by a mechanism independent of carbohydrate metabolism.