Comparative effects of some calcium-channel blockers on human peripheral arteries and veins

We investigated the effects of five different calcium-channel blockers (CCBs), verapamil, nifedipine, diltiazem, flunarizine and lidoflazine, on contractions evoked in vitro by noradrenaline (NA) in small human arteries and veins from the epigastric region. Vessels were obtained from patients without obvious vascular diseases undergoing surgery because of inguinal hernias. The human superficial epigastric artery has previously been shown to contain mainly alpha 1-adrenoceptors, whereas in the vein alpha 2-adrenoceptors predominate. In experiments where NA (10(-5) M) was added non-cumulatively, it was found that nifedipine was the most potent relaxant agent in both arteries and veins, but that this drug showed no preference for any type of vessel. In contrast verapamil (10(-6) M) and (10(-5) M) diltiazem, flunarizine and lidoflazine inhibited the NA-induced contractions to a significantly greater extent in the arteries than in the veins. Comparison between diltiazem and nifedipine on contractions induced by cumulative addition to NA showed that both drugs had significantly more depressive effects on arteries than on veins if the vessels were contracted by relatively high concentrations of NA (10(-6) and 10(-5) M). The results thus confirm the clinical finding that CCBs have more pronounced effects on the arterial than on the venous side of the circulation. They do not support the view that CCBs are more effective inhibitors of alpha 2- than alpha 1-adrenoceptor mediated contraction in isolated human blood vessels.