Betamethasone effects on steroid and prostaglandin concentrations in pregnant rhesus monkeys.

Glucocorticoids delay parturition in rhesus monkeys, but the mechanism is unknown. This study was designed to determine the relationship between administration of glucocorticoids and prostaglandin levels in late pregnancy. Pregnant rhesus monkeys received intramuscular betamethasone (2 mg/day) from day 120 to day 133 of pregnancy. 13,14-Dihydro-15-keto-prostaglandin F2 alpha, progesterone, estradiol, estrone, and cortisol in amniotic fluid were measured by radioimmunoassay, and progesterone and estradiol were measured in the maternal serum. Among control animals, between 133 days and 160 days there were significant increases in adrenal size (p less than 0.05) and in amniotic fluid 13,14-Dihydro-15-keto-prostaglandin F2a metabolite, (p less than 0.005), estrone, and progesterone concentrations (p less than 0.05). The increase in adrenal size and the rise in amniotic fluid 13,14-Dihydro-15-keto-prostaglandin F2a metabolite, did not occur in betamethasone-treated monkeys. Maternal serum estradiol levels were suppressed immediately after treatment with betamethasone but recovered to control levels by day 160. Other changes in maternal serum and amniotic fluid sex steroid levels were sought but not observed. These data are consistent with the hypothesis that glucocorticoids delay primate parturition by altering intrauterine prostaglandin F2 alpha metabolism.