A comparison of several calcium antagonists on uterine, vascular and cardiac muscles from the rat.

An assessment was made of the potencies of nifedipine, gallopamil, diltiazem, cinnarizine and salbutamol as inhibitors of tension development by the uterus and cardiovascular tissues from the term pregnant rat. The rank order of potency was nifedipine greater than gallopamil greater than diltiazem for those preparations on which these compounds were potent, viz. spontaneous and oxytocin-induced tension development of the uterus, spontaneous tension development of hepatic portal vein, potassium chloride (KCl)-induced pressure rises of perfused mesenteric bed and electrically-stimulated (0.5 Hz) ventricular muscle. The rank order of potency of nifedipine, gallopamil and diltiazem was different for those preparations on which they exhibited low potency, viz. noradrenaline-induced pressure rises of perfused mesenteric bed and tension development of aorta. Gallopamil and diltiazem, but not nifedipine, were more potent against tension development by ventricular muscle stimulated at 2.5 Hz than at 0.5 Hz, suggesting that nifedipine interacts at a different site from the other compounds. Cinnarizine was less potent than the other calcium antagonists on the uterus and portal vein, was the second most potent compound against KCl-induced pressure rises of the mesenteric bed and was equipotent against responses to noradrenaline and KCl of the mesenteric bed (unlike the other compounds). This suggests that the site of action of cinnarizine differs from that of the other calcium antagonists. Nifedipine, gallopamil and diltiazem, like salbutamol, exhibited selectivity for inhibition of tension development by the uterus relative to the cardiovascular tissues.