Noninvasive evaluation of cardiac dysfunction by echocardiography in streptozotocin-induced diabetic rats

Background: There has not been a noninvasive in vivo longitudinal evaluation of cardiac function in diabetic rats. The objective of this study is to examine the time course of development of cardiac dysfunction in streptozotocin (STZ)-induced diabetic rats. Methods and Results: Cardiac function was evaluated by M-mode and Doppler echocardiography in anesthetized Wistar rats at 2, 4, 5, 6, and 8 weeks after injection with 65 mg of STZ/kg and in age-matched control rats before and after the administration of isoproterenol. Body weight (BW) was significantly less and blood glucose level significantly greater in diabetic rats compared with controls at 2 weeks and remained at these levels at all time points. The calculated left ventricular (LV) mass appeared slightly decreased in diabetic rats. However, LV mass-BW ratios were similar in controls and diabetic rats at 3, 4, and 5 weeks, but were significantly greater in diabetic rats at 6 and 8 weeks. Basal heart rate (HR) was significantly lower in diabetic rats at all time points studied. Basal LV systolic and diastolic dimensions, fractional shortening (FS), velocity of circumferential shortening (Vcf), peak emptying rate (PER), peak filling rate (PFR), and aortic peak velocity (APV) were not significantly different between controls and diabetic rats at 2 and 4 weeks. PER and PFR were significantly less in 5-week diabetic rats. However, Vcf, PER, and PFR were significantly less and FS and APV were similar at 6 and 8 weeks. Administration of isoproterenol increased HR, Vcf, FS, PFR, and PER in controls at all time points, but the increases in diabetic rats at 5, 6, and 8 weeks were less compared with those in controls. The increase in APV was significantly less in diabetic rats at all time points studied. Conclusion: STZ-induced diabetic rats showed bradycardia before contractile dysfunction. Overt and covert contractile dysfunction unmasked by isoproterenol begins at 5 weeks of diabetes. The overt LV systolic and diastolic dysfunction are fully manifested after 6 weeks of diabetes.