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Changes in Fetal Plasma Corticotropin-Releasing Hormone during Androstenedione-Induced Labor in the Rhesus Monkey: Lack of an Effect on the Fetal Hypothalamo-Pituitary-Adrenal Axis¹

Laboratory for Pregnancy and Newborn Research, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853-6401

Address all correspondence and requests for reprints to: Peter W. Nathanielsz, M.D., Ph.D., Sc.D., Laboratory for Pregnancy and Newborn Research, Department of Physiology, T9 015 VRT, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853-6401. E-mail: pwn1{at}cornell.edu

Androstenedione infusion to pregnant monkeys leads to premature labor and live delivery. Androstenedione-induced labor also increased placental CRH messenger RNA and peptide to concentrations observed at term in pregnant monkeys. Placental CRH may modulate fetal pituitary-adrenal function during pregnancy in primates. This study tested the hypothesis that androstenedione-induced premature delivery in pregnant monkeys results from androstenedione-induced increases in placental CRH, which stimulate premature activation of the fetal pituitary-adrenal axis. The hypothesis was tested by comparing fetal umbilical vein (FUV) plasma CRH, ACTH, dehydroepiandrosterone sulfate, and cortisol concentrations at cesarean section in fetuses from mothers undergoing spontaneous, term labor (group I), with those in fetuses from mothers undergoing androstenedione-induced, premature labor (group II) and with those from mothers not in labor (group III). In addition, gestation-related changes in maternal plasma CRH concentrations were investigated, and CRH immunoactivity was characterized by Sephadex G50 chromatography in pooled maternal plasma extracts.

FUV CRH concentrations were similarly elevated in group I and group II fetuses, compared with group III fetuses. Despite similar FUV blood gases in all fetuses, FUV ACTH and dehydroepiandrosterone sulfate concentrations were higher in group I fetuses than in group II or group III fetuses. The majority of CRH immunoactivity coeluted with synthetic human CRH. Maternal plasma CRH concentrations showed a modest increase with gestation in the rhesus monkey.

These data: 1) demonstrate that androstenedione treatment of pregnant monkeys at 0.8 of gestation elevates fetal plasma CRH to similar concentrations measured at term; 2) do not support the hypothesis that androstenedione-induced delivery in the monkey results from premature activation of the fetal pituitary-adrenal axis by placental CRH; but 3) do support a role for activation of the fetal hypothalamo-pituitary-adrenal axis in association with spontaneous term labor in the monkey; and 4) demonstrate important interprimate species differences in maternal CRH physiology.

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