Effects of the novel coronary selective calcium channel blocker, McN-6186, on cardiocirculatory dynamics, coronary vascular resistance, and cardiac output distribution in normal, conscious rats.

The purpose of this study was to characterize the cardiocirculatory effects of the novel calcium channel blocker, McN-6186 (McN), normal, conscious rats. Animals were instrumented under halothane anesthesia for right atrial, left ventricular, arterial, and venous pressure recordings. The radioactive microsphere technique was used to measure regional blood flow (RBF) and cardiac output (CO) before (control) and during intravenous (i.v.) infusion of either McN at three doses (0.03, 0.1, 0.3 mg/kg) or vehicle at an equal infusion rate (0.0408 ml/min). Nifedipine (NIF) was also studied at three similar blood pressure (BP)-lowering doses (0.025, 0.150, and 0.375 mg/kg). The predominant effect of McN in conscious rats was to cause coronary vasodilation. The coronary vasodilator potency of McN was similar to NIF (ED25, McN = 0.03 mg/kg, NIF = 0.025 mg/kg). Neither McN nor NIF significantly changed systemic vascular resistance (SVR) over their respective coronary vasodilator dose ranges, suggesting that both compounds are selective coronary vasodilators. The doses of McN and NIF that reduced mean arterial pressure (MAP) by 25% (ED25) were similar (McN = 0.3 mg/kg, NIF = 0.375 mg/kg). At equal BP-lowering doses, McN increased coronary flow by 145% versus 110% for NIF. McN did not have major effects on other regions of the peripheral circulation. There was, however, some vasodilator activity in the renal and cerebral vascular beds. Because McN reduced coronary vascular resistance at a dose lower than that required to reduce resistance in other vascular beds, this compound appears to be a selective coronary vasodilator and may have therapeutic efficacy as an antianginal agent.