Influence of sex, diabetes and ethanol on intrinsic contractile performance of isolated rat myocardium.

The influence of sex on intrinsic contractile performance, diabetes-induced myocardial mechanical dysfunction and the inotropic response to clinically relevant concentrations of ethanol (ETOH) was studied using weight-matched streptozotocin-induced diabetic rats. After 8 weeks, isolated left-ventricular papillary muscles stimulated at 0.5 Hz, were studied under isometric conditions at Lmax. Peak developed tension, time-to-peak tension (TPT), time-to-90% relaxation (RT90), and the maximum velocities of tension development and rate of tension decay were assessed at baseline and in response to changes in stimulation frequency and varying extracellular calcium concentrations. In male but not in female rats, body weight and heart size were significantly correlated with glycemic status. In both sexes, diabetes was associated with prolongation of baseline TPT and RT90 values. However, diabetes-induced prolongations of contraction and relaxation duration were greater in papillary muscles obtained from male than in those from female animals. The negative staircase effect of increasing the frequency of stimulation was not influenced by sex or the diabetic state. Similarly, neither the positive, inotropic effect of increasing extracellular calcium nor the negative inotropic effect of ethanol was modified by sex or experimental diabetes. Our results suggest that: 1) myocardium from female rats is resistant to diabetes-induced myocardial dysfunction and 2) neither baseline developed tension, calcium-mediated nor ethanol-induced inotropic responsiveness are influenced by sex or experimental diabetes.