Effect of nicardipine on human placental vasculature

The effect of nicardipine on segments of human chorionic arteries and veins was studied. Nicardipine induced the concentration-dependent inhibition of K+ (75 mM) contractions in both kinds of vessels. Preincubation of these vessels with nicardipine (10(-5) M, which produced maximal reduction of K+ responses) caused a greater decrease of contractions induced by K+ (75 mM) than of those induced by serotonin (10(-6) M). Ca suppression from the medium reduced the responses elicited by serotonin and practically abolished those induced by K+. The subsequent Ca addition induced contractions which were diminished by nicardipine (10(-5) M) in both types of vessels. Nicardipine also attenuated serotonin contractions in Ca-free medium, especially in veins. Both serotonin (10(-6) M) and K+ (75 mM) increased 45Ca uptake. This effect was decreased by nicardipine (10(-5) M), mainly in veins. Basal 45Ca uptake was unaffected by this Ca antagonist. These findings indicate that human chorionic vessels are sensitive to nicardipine; the responses mediated by Ca entry through voltage-dependent Ca channels are inhibited to a greater extent by this Ca antagonist than those mediated by receptor-dependent Ca channels.