Changes in cardiac contractility in IDDM and NIDDM diabetic rats

Differences in myocardial contractility were studied in type I (insulin-dependent, IDDM) and type II (non-insulin-dependent, NIDDM) diabetic rats. Using the streptozotocin-induced diabetes as an experimental model, the contractile properties of left ventricular myocardium of IDDM and NIDDM animals were compared to similar parameters of their age-matched controls. Contraction force was analyzed as a function of the pacing frequency. Paired-pulse stimulation and catecholamine treatment were applied to compare the inotropic responses obtained in the two types of diabetes. Diabetic and control preparations developed equal peak tension at each driving frequency upon the application of paired-pulse stimulation with fixed interpulse interval. The interpulse interval dependence of paired-pulse induced inotropy was altered and the velocity of contraction and relaxation decreased in IDDM, but not in NIDDM muscles. Sensitivity to isoproterenol and norepinephrine was decreased in both types of diabetes, however, the isoproterenol resistance of old diabetic animals was attributable to age rather than to the diabetic state. The results indicate that alterations in the contractile parameters and catecholamine sensitivity in IDDM differ from those observed in NIDDM form of diabetes mellitus.