DIFFERENTIAL-EFFECTS OF BETAMETHASONE AND DEXAMETHASONE FETAL ADMINISTRATION OF PARTURITION IN SHEEP

OBJECTIVE: We tested the hypothesis that betamethasone is more potent than dexamethasone in inducing the essential mechanisms of parturition in sheep. METHODS: Twenty-one sheep were instrumented under general a nesthesia with maternal and fetal arterial and venous catheters and my ometrial electromyogram electrodes at 117 days' gestation (dGA). At 12 5 dGA at 12:00 PM, after 2 days of baseline recording, either saline ( n = 7, control group), betamethasone (n = 7), or dexamethasone (n = 7) was administered into the fetal jugular vein at a rate of 10 mu g/hou r. A total dose of 0.48 mg was given over the next 48 hours. The anima ls underwent autopsy 3 days after the end of the infusion period (130 dGA), or earlier if labor resulted from the glucocorticoid administrat ion. Daily maternal and fetal arterial blood samples (4 mL) for hormon e measurement were taken at 10:00 AM throughout the study period. Addi tional arterial blood samples were taken if the animal developed labor . Maternal plasma progesterone and fetal ACTH and cortisol concentrati ons were measured by radioimmunoassay, and corticosteroid-binding glob ulin (CBG) binding capacity was determined by saturation analysis. Myo metrial activity was monitored continuously throughout the experimenta l protocol. RESULTS: All seven betamethasone-treated animals developed labor after the glucocorticoid infusion regimen. In contrast, only tw o of seven dexamethasone-treated animals developed labor. Fetal treatm ent with betamethasone produced a greater and earlier fall in maternal plasma progesterone than fetal treatment with dexamethasone. Elevated fetal plasma ACTH and cortisol concentrations at the end of the infus ion period in both betamethasone-and dexamethasone-treated animals wer e not related to the development of labor-type contraction. CONCLUSION S: These data support the hypothesis that betamethasone is more potent than dexamethasone in including the essential mechanisms of parturiti on is sheep. Copyright (C) 1996 by the Society for Gynecologic Investi gation.