Verapamil, diltiazem and nifedipine inhibit vascular responses to noradrenaline, acetylcholine and 5-hydroxytryptamine in human saphenous vein.

Verapamil (0.02-2 microM), diltiazem (0.22-8.14 microM) and nifedipine (0.29-8.96 microM) produced concentration-dependent relaxation of human isolated saphenous vein. Based on the EC50 values of the calcium entry blockers, verapamil (relative potency = 1) was 7 and 5 times as potent as nifedipine and diltiazem, respectively, in producing relaxation of the human saphenous vein. In addition, verapamil, diltiazem and nifedipine inhibited the vascular responses (i.e. contractions) produced by noradrenaline (0.03-36 microM), acetylcholine (0.05-55 microM) and 5-hydroxytryptamine (0.02-25 microM) and to KCl (10-100 mM). It was concluded that verapamil, diltiazem and nifedipine relaxed the human isolated saphenous vein, verapamil being more potent than diltiazem or nifedipine, and modified the vascular response to vasoconstrictor agents, e.g. noradrenaline, acetylcholine, 5-hydroxytryptamine and KCl. Thus verapamil, diltiazem and nifedipine may inhibit calcium influx through both potential and receptor-operated calcium ion channels.