Oxytocin, Prostaglandins, and Contractility of the Human Uterus at Term Pregnancy

The contractile properties of myometrial "mini-strips" from the upper and lower uterine segments were studied by a superfusion technique. These samples of myometrium were taken from women delivered by elective cesarean section in the 39th week of pregnancy. The frequency of spontaneous contractions was significantly higher in isthmic myometrial specimens than in corpus specimens, whereas amplitude and duration of contractions did not differ. Both isthmic and corpus myometrium were stimulated by prostaglandin E2 at low concentrations and inhibited at high concentrations. PGF2 alpha induced an excitory response in the isthmic strips but surprisingly not in preparations from the corpus. However, PGF2 alpha restored normal spontaneous activity following inhibition of the contractility with indomethacin. Oxytocin caused an excitory response over a wide concentration range in both types of specimen and this response was not reduced by pretreatment with indomethacin. These findings suggest that endogenous prostaglandin synthesis is a necessary prerequisite for spontaneous myometrial activity at term pregnancy and that prostaglandins are not essential for the excitatory effect of oxytocin.