The influence of streptozotocin-induced diabetes on myocardial contractile performance in vitro.

The influence of streptozotocin-induced diabetes has been studied on rabbit isolated cardiac muscle responses to noradrenaline and calcium. Seven weeks after treatment with streptozotocin (70 mg/kg i.v.), right atrial contractile rate was found to be depressed, whereas left ventricular papillary muscle function was markedly enhanced. Neither the atrial nor the ventricular (papillary) muscle strip exhibited a remarkable alteration in sensitivity to noradrenaline. Although sensitivity to calcium was not altered in the atrial muscle, papillary muscle strips obtained from diabetic rabbits were supersensitive to calcium. These results suggest that in diabetic animals, right atrial pacemaker function is depressed, while ventricular muscle activity is enhanced. In the diabetic state, this enhanced ventricular muscle function is likely to be associated with an alteration in calcium utilization.