RELAXATION OF LARGE CORONARY-ARTERY BY VERAPAMIL, D600, AND NIFEDIPINE IS CONSTRICTOR SELECTIVE - COMPARISON WITH GLYCERYL TRINITRATE

Abstract

We compared the vasodilator potencies of a number of Ca2+-entry blockers with glyceryl trinitrate (GTN) in isolated ring segments of dog coronary arteries contracted by a variety of substances. Rings were contracted to 80% of maximum by serotonin, phenylephrine (PE), noradrenaline (NA), K+ (KCl), or U46619 (stable thromboxane A2 analogue). Cumulative additions of a vasodilator then relaxed the ring towards basal tone. GTN had a similar IC50 value (0.1 - 0.3 microM) regardless of the substance used to contract the ring. In contrast, nifedipine and verapamil were weak relaxant drugs against arteries contracted by U46619. Nifedipine was most potent in rings contracted by K+, whereas verapamil w..