Inhibition of premature labor in sheep by a combined treatment of nimesulide, a prostaglandin synthase type 2 inhibitor, and atosiban, an oxytocin receptor antagonist

Objective: The aim of this study was to compare the effects of the selective prostaglandin synthase type 2 inhibitor nimesulide, alone or in combination with the oxytocin receptor antagonist atosiban, on the progression of glucocorticoid-induced premature labor in sheep. Effects on circulating maternal and fetal prostaglandin concentrations and on fetal well-being were also examined. Study Design: Premature labor was induced in ewes with long-term catheterized fetuses by infusion of dexamethasone (1 mg/d) starting at 138 ± 1 days’ gestation. Ewes also received an infusion of either nimesulide and atosiban (20.0 and 4.12 mg/kg per day, respectively; N = 5), nimesulide alone (20.0 mg/kg per day; N = 5), or vehicle only (n = 9). Plasma 13,14-dihydro-15-keto-prostaglandin F2α and prostaglandin E2 concentrations were measured before and during infusions in plasma samples obtained from the maternal and fetal carotid arteries and the utero-ovarian vein. Results: No fetuses from ewes treated with nimesulide and atosiban were delivered during treatment. These animals were killed electively 98.0 ± 6.8 hours after the commencement of dexamethasone induction. This was significantly longer than the delivery times for those ewes treated with nimesulide alone (71.2 ± 3.9 hours; N = 5) and for vehicle-treated ewes (51.4 ± 1.7 hours; N = 9). Both maternal and fetal plasma 13,14-dihydro-15-keto-prostaglandin F2α and prostaglandin E2 concentrations in nimesulide and atosiban–treated ewes and in nimesulide-treated ewes decreased during treatment. In contrast, vehicle-treated ewes showed a significant increase in maternal and fetal plasma 13,14-dihydro-15-keto-prostaglandin F2α and prostaglandin E2 concentrations during dexamethasone induction. Uterine electromyographic activity observed in nimesulide and atosiban–treated ewes was significantly suppressed with respect to activities in both vehicle- and nimesulide-treated ewes during the treatment period. All fetuses were alive at delivery or scheduled death. Conclusions: These results indicate that the combination of an inhibitor of prostaglandin endoperoxidase H synthase type 2 with an oxytocin receptor antagonist is more effective in inhibition of preterm labor than is treatment with a prostaglandin endoperoxidase H synthase type 2 inhibitor alone. The clinical use of atosiban to prevent the oxytocin-stimulated increase in uterine activity associated with labor in combination with nimesulide may permit reduction of the dose of nimesulide used to a level that has minimal impact on fetal well-being. (Am J Obstet Gynecol 2000;183:649-57.)