Effect of nifedipine in arterial vasculature of human placenta

1. Nifedipine induced concentration-dependent relaxations in segments of human placental arteries precontracted with 40 mM K+. 2. Preincubation of segments with nifedipine induced concentration-dependent inhibition of contractions elicited by 40 mM K+ (IC50, 2.5 x 10(-9) M) and 10(-7) M 5-HT (5.9 x 10(-8) M). 3. The time-course of contractions elicited by K+ and 5-HT (responses not sustained) in the absence and in the presence of nifedipine was different. 4. Nifedipine inhibited Ca addition-evoked contractions in Ca-free medium containing 40 mM K+ or 10(-7) M 5-HT, mainly those obtained in depolarized segments. 5. These results indicate that these arteries are very sensitive to nifedipine and that the voltage-operated Ca channels are more affected by the Ca antagonist than receptor-operated ones.