The potencies and selectivities of four calcium antagonists as inhibitors of uterine contractions in the rat in vivo

Abstract

The potencies of four calcium antagonists (nifedipine, gallopamil, verapamil and diltiazem) at inhibiting uterine contractions in vivo have been assessed in the conscious ovariectomized, post‐partum rat. Their selectivities for this action, relative to their effects on blood pressure and heart rate, have been compared with salbutamol. All compounds produced a dose‐dependent inhibition of intra‐uterine pressure cycles. The rank order of potency was salbutamol >nifedipine > diltiazem = gallopamil > verapamil. All compounds produced a dose‐dependent fall of mean blood pressure. The rank order of potency was salbutamol > nifedipine > gallopamil > verapamil > diltiazem. Salbutamol and nifedipine produced a tachycardia, which was very marked with salbutamol. Gallopamil, verapamil and diltiazem induced a moderate tachycardia at low doses but temporary cessation of heart beat occurred at high doses. Nifedipine and diltiazem, like salbutamol, exhibited some selectivity for inhibition of uterine contractions relative to their cardiovascular actions. Gallopamil and verapamil showed no selectivity for the uterus.