Antiarrhythmic, Electrophysiological and Haemodynamic Effects of Prolonged Oral Dosing with Org 7797 in the Anaesthetized Rat

The antiarrhythmic, electrophysiological and haemodynamic effects of chronic oral administration of Org 7797 ((16 alpha,17 beta)-17-methylamino-oestra-1,3,5(10)-triene-3, 16-diol-(Z)-2-butonedioate) were studied in rats. During dosing (10 mg kg-1 twice a day for 10 days) no effects on the electrocardiogram, monitored in conscious animals, were observed despite modest reductions (15-18%) in the maximum rate of depolarization of papillary muscle excised 1 or 6 h after completion of the dosing regime. Following anaesthesia, Org 7797 reduced the severity of arrhythmias induced by coronary artery occlusion and prevented the accompanying decrease in the ventricular fibrillation threshold (VFT) at 1 h after completion of dosing. By 6 h the effect on VFT had waned but protection against ischaemia-induced arrhythmias was retained despite a substantial decrease in Org 7797 plasma levels. Drug treatment did not modify arterial blood pressure, heart rate or stroke volume. We conclude that Org 7797 given chronically via the oral route exerts antiarrhythmic actions which may, at least in part, be due to sodium-channel block. In addition, our results suggest the presence of an active metabolite. The protective effects of Org 7797 were seen in the absence of electrocardiographic or haemodynamic changes suggesting that multiple oral doses of Org 7797 do not compromise normal cardiac function.