The effects of some synthetic prostanoids on the contractility of the human lower uterine segment in vitro.

We have investigated the ability of three synthetic prostanoids to directly influence uterine contractility by studying the effects in vitro. Strips of lower uterine segment smooth muscle were obtained from women undergoing elective cesarean section at term. The ability of these strips to develop tension in the presence of cumulative additions of prostanoids or oxytocin was assessed. Spontaneous contractions were inhibited by ZK 96.480, a stable synthetic analog of prostaglandin I2, with a 50th percentile effective concentration (EC50) of 8 nmol/L. Both sulprostone, an analog with selectivity for some of the actions of prostaglandin E2, and U-44069, a stable thromboxane A2 mimetic, caused excitation with EC50s of 20 and 16 nmol/L, respectively. The EC50 for oxytocin was 6 nmol/L. There were no significant differences in the maximal tensions developed in response to the excitatory prostanoids or oxytocin.