Relaxant Effects of Nifedipine on Isolated, Human Myometrium

Abstract

Myometrial tissue was obtained from nonpregnant women subjected to hysterectomy due to various gynecological disorders and from women undergoing cesarean section. Strip preparations were dissected and isometric tension was recorded. Nifedipine (2.9 .times. 10-8-2.9 .times. 10-6 M) inhibited spontaneous contractile activity, mainly by reducing the amplitude of contraction in both nonpregnant and pregnant myometrium. The drug inhibited K-induced contractions in a concentration dependent manner. The effect was more pronounced in pregnant than in nonpregnant tissue. In preparations of pregnant human myometrium, normally polarized or K depolarized, oxytocin induced a contractile activity that was effectively inhibited by nifedipine. Nifedipine relaxed contractions induced by vasopressin in isolated nonpregnant myometrium. Apparently, the relaxant effect of nifedipine on isolated pregnant and non-pregnant human myometrium can be explained by inhibition of Ca influx. Apparently Ca influx is an important step in the initiation of contractile activity in human uterine smooth muscle.