Cardiac actions of AQ-A 39, a bradycardic agent.

Abstract

Cardiac and coronary vasodilator actions of AQ-A 39, a new bradycardic agent which resembles verapamil in chemical structure, were investigated in various isolated, blood–perfused dog-heart preparations. AQ-A 39 was injected intra–arterially. In all preparations, AQ-A 39 increased blood flow. In sino-atrial(SA) node preparations, AQ-A 39 decreased sinus rate, but rarely produced atrial standstill even in large doses. In paced atrioventricular(AV) node preparations AQ-A 39 injected into the posterior septal artery supplying the AV node rather increased AV conduction time in large doses, but produced neither second- nor third-degree AV block. In the same preparations, AQ-A 39 injected into the anterior septal artery supplying the His-Purkinje-ventricular system rather prolonged AV conduction time in large doses. In paced papillary muscle preparations, AQ-A 39 reduced force of contraction only in large doses. In spontaneously beating papillary muscle preparations, AQ-A 39 decreased rate of automaticity and force of contraction as well. The order of effectiveness of AQ-A 39 on the cardiovascular variables is as follows: Ventricular automaticity = SA nodal automaticity >> AV nodal conduction = intraventricular conduction = coronary blood flow = ventricular muscle contraction. These results indicate that AQ-A 39 has a pharmacological profile entirely different from that of verapamil.