Effect of insulin replacement on streptozotocin-induced effects in the rat heart.

Streptozotocin (65 mg/kg) was used to induce diabetes in male Sprague-Dawley rats. Isolated cardiac tissue exhibited a systematic depression in atrial pacemaker function and an enhancement in ventricular function accompanied by a supersensitivity to calcium relative to control animals. beta-Adrenoceptor density was found to be significantly lowered in the treated animals. However, no change in responsiveness of the tissues to isoproterenol was observed. The systematic changes in atria and ventricle were found to be completely and partially reversed respectively, by daily administration of 4-5 units of Ultralente (U-100) insulin, whereas the decrease in beta-adrenoceptor number and supersensitivity to calcium were completely reversed. These results suggest that STZ by itself might not have toxic effects in the heart and that its effects may be overcome by chronic insulin-replacement.