Influence of insulin treatment on the mechanical properties and inotropic response to ethanol in diabetic myocardium.

Abstract

Diabetes significantly affects cardiac performance, as does ethanol. To assess whether insulin treatment alters the inotropic response to acute ethanol exposure and reverses diabetes-induced myocardial dysfunction, male Wistar rats were made diabetic using streptozocin, 55 mg/kg intravenously. The inotropic effect of ethanol on normal, diabetic, and insulin-treated (8 weeks) diabetic animals was studied using isolated, left-ventricular papillary muscle preparations superfused with Tyrode's solution under isometric conditions. Peak tension developed, time to peak tension (TPT), time to 90% relaxation (RT90), maximum rate of tension developed (+VT), and maximum rate of fall in tension (-VT) were determined in the absence and presence of clinically relevant concentrations of ethanol for 10 minutes. In insulin-treated diabetic muscles, baseline developed tension, +VT, and -VT were enhanced, and the prolongation of TPT and RT90, characteristic of diabetic myocardium, was attenuated. The magnitude of the reduction in developed tension in response to ethanol, 80 mg/dL, was slightly greater in untreated diabetic myocardium. Higher concentrations of ethanol (120 to 240 mg/dL) decreased tension in all groups and was of similar magnitude. The negative inotropic effect of higher ethanol concentrations was associated with shortening of TPT and RT90, as well as a diminution of +VT and -VT. It is concluded that with insulin treatment, the mechanical properties of diabetic myocardium are normalized; however, neither the myocardium's sensitivity to ethanol nor the overall magnitude of ethanol's negative inotropic effect is modified by insulin treatment.