Effects of calcium antagonists on serotonin and noradrenaline venoconstriction in humans

The activity of some calcium antagonists on 5-hydroxytryptamine (5HT) and noradrenaline-induced venoconstriction has been evaluated in humans. Oral doses of nimodipine, 30 mg, and nifedipine, 10 mg, but not of verapamil, 80 mg, and flunarizine, 10 mg, inhibit 5HT-induced venoconstriction of the dorsal hand vein. Nimodipine, but not verapamil and flunarizine, inhibit noradrenaline-induced venoconstriction as well. Verapamil, locally administered into the hand vein, inhibits 5HT and noradrenaline-induced venoconstriction. These results suggest that only calcium antagonists of the dihydropyridine type have antivenoconstrictive activity in the hand vein at oral clinical doses, whereas verapamil is active only if administered by the intravenous route, which probably produces local plasma concentrations higher than those reached with the oral clinical doses.