Inhibitory effect of iloprost on the contractility of lower uterine segment myometrium from rhesus monkeys in normal-term and androstenedione-inducedpreterm labor

OBJECTIVE: Iloprost, a combined EP1 stimulatory and IP inhibitory receptor agonist, was rested in vitro on myometrium from the lower uterine segment o f pregnant rhesus monkeys to compare its effects in spontaneous labor and i n labor induced by the administration of androstenedione to the mother. METHODS: Pregnant rhesus monkeys carrying fetuses of known gestational age were instrumented under halothane general anesthesia with femoral artery an d vein catheters and uterine electromyogram leads. Experimental animals wer e infused with androstenedione from 139 days' gestation. Control animals we re infused with intralipid vehicle from 139 days' gestation. Lower uterine segment myometrium was removed from control animals either before labor beg an (n = 6) or in spontaneous labor (n = 4) and from animals undergoing prem ature labor induced by androstenedione (n = 4). Myometrial contractility in response to iloprost was evaluated using a superfusion system in vitro. RESULTS: Iloprost was inhibitory oil myometrium obtained from the lower ute rine segment from androstenedione-treated animals as well as vehicle-infuse d animals in spontaneous term labor. In contrast, iloprost had no effect on myometrial strips from control animals not in labor. CONCLUSION: These findings indicate up-regulation of IP receptors which inh ibit myometrial contractility and/or down-regulation of EP1 receptors which stimulate myometrial contractility in the lower uterine segment during lab or. A relative increase ill inhibitory responses in the lower uterine segme nt during labor may enable this region to dilate to allow passage of fetus. Copyright (C) 2000 by the Society for Gynecologic Investigation.