Acute intrauterine hypoxia increases amniotic fluid prostaglandin F metabolites in the pregnant sheep

OBJECTIVE: Amniotic fluid infection promotes cytokine release, prostaglandin production, and premature labor. In several tissues local hypoxia also activates the secretion of cytokines. Many patients initially seen in premature labor carry small-for-gestational-age fetuses, a condition associated with intrauterine hypoxia. The purpose of our study was to determine whether a reduction in placental blood flow and subsequent acute hypoxia affects prostaglandin secretion by the placenta. STUDY DESIGN: We chronically catheterized six pregnant sheep at 120 days of gestation. We placed catheters in the maternal and fetal femoral arteries and in the amniotic fluid cavity. A flow probe and snare were placed around the common uterine artery. RESULTS: A 30-minute uterine circulation occlusion of 30% of its control value produced an increase in prostaglandin F metabolite from 790 ± 157 to 944 ± 184 pg/ml within 10 minutes (p < 0.01). Additional uterine blood flow reduction to 60% of control increased the amniotic fluid prostaglandin F metabolites concentration to 894 ± 202 (p < 0.05, analysis of variance). No increase in mean intrauterine pressure was detected (p > 0.1). CONCLUSIONS: We speculate that the prostaglandin increase in amniotic fluid in response to intrauterine hypoxia could eventually lead to premature labor. Whether the increase in prostaglandins is mediated by changes in cytokines is unknown at the present time.