Article: PDF OnlyCoronary Vasodilator Versus Cardiac Effects of MCI-176, a Novel Quinazolinone Calcium Antagonist, in the Dog HeartHosono, Makoto; Taira, NorioAuthor Information Department of Pharmacology, Tohoku University School of Medicine, Sendai, Japan Journal of Cardiovascular Pharmacology: June 1987 - Volume 9 - Issue 6 - p 633-640 Free Abstract We compared the coronary vasodilator and cardiac effects of MCI-176, a novel quinazolinone calcium antagonist, in isolated, blood-perfused sinoatrial (SA) node, atrioventricular (AV) node, and papillary muscle preparations of dogs. The drug was administered intraarterially. In SA node preparations MCI-176 reduced sinus rate and produced atrial standstill in large doses. In AV node preparations MCI-176 prolonged AV conduction time and produced second- or third-degree AV block in large doses only when administered into the artery supplying the AV node, but failed to affect AV conduction when administered into the artery supplying the His-Purkinje-ventricular system. In paced papillary muscle preparations MCI-176 reduced the force of contraction. In spontaneously beating papillary muscles MCI-I76 failed to change the beating rate. MCI-176 increased blood flow in all preparations. The dose that doubled blood flow was slightly larger than the dose that produced a 15% increase in AV conduction time, but about one-third the dose that produced a 15% decrease in sinus rate. The dose estimated to reduce the force of contraction by half was more than $10 times the dose that doubled blood flow. The results indicate that MCI-176 can be classified as a nonvasoselective calcium antagonist but that it differs from others. © Lippincott-Raven Publishers.