Objective To study the relation of calcium entry into myometrium and uterus phasic
contraction in vitro induced by a saponin
extract:
gongxuening. Methods Tension measurement of rat myometrium strips was used to observe the effect of nitrendipine and verapamil (calcium channel blockers) on the tensility change of rat myometrium strips which was induced by gongxuening. Results Gongxuening 50 μg/ml could induce phasic uterus contractions in Machfield Krebs′solution and in calcium-free solution. The phasic uterus contractions were not observed with the concentration of gongxuening from 25 μg/ml to 200 μg/ml.In the solution with a half concentration of calcium,the amplitude and frequence of uterus
contraction induced by different concentrations of gongxuening were significantly lower than those in common solution of calcium channel blockers,such as nitrendipine and verapamil;the inhibition of uterus contraction induced by gongxuening and oxytocin was in dose-dependent manner,but the uterus contraction induced by gongxuening was more sensitive to calcium channel blockers than that induced by oxytocin. Conclusion Gongxuening is a saponin extract,its uterotonic effect depends on the occurrence of extracellalar calcium;the action mechanism may ascribe to promoting the smooth muscle′s extracellular calcium ions to flow inwards.