Chronic effects of streptozotocin diabetes on myocardial sensitivity in the rat.

One month after streptozotocin treatment, basal rate in spontaneously beating right atria was decreased and basal developed force in electrically-driven right ventricular tissue was increased. Atrial sensitivity to the chronotropic effects of isoproterenol was not altered. In contrast, sensitivity in ventricular tissue to the inotropic effects of isoproterenol was decreased while sensitivity to calcium was increased. Associated with these changes was a decrease in myocardial beta-adrenoceptor density. Data obtained 3 and 6 months after streptozotocin treatment were similar to the observed alterations at 1 month. These results suggest that alterations in the chronotropic and inotropic responses that are expressed within 1 month after streptozotocin treatment do not significantly progress during the 6 months following induction of diabetes. They therefore reveal the independence of myocardial alterations from age of the animal and duration of diabetes (up to 6 months).