Estrogen regulation of the pregnant baboon placental 11beta-hydroxysteroid dehydrogenase (11beta-HSD)-catalyzed metabolism of cortisol and cortisone and its effect on the development of the fetal hypothalamic-pituitary-adrenal axis.

摘要

Pepe and Albrecht previously demonstrated that the estrogen-regulated change in transuteroplacental metabolism of cortisol (F) and cortisone (E) from preferential reduction (E to F) at midgestation to oxidation (F to E) near term results in a decline of bioactive cortisol crossing the placenta and reaching the fetus culminating in activation of the hypothalamic-pituitary adrenal axis of the baboon and the ontogenesis of rate-limiting steroidogenic enzymes culminating in de novo F secretion. Protein kinase A (PK-A) activity in the baboon fetal adrenal gland cytosolic fraction was increased 2-fold both at term [day 165 of gestation (term = 184 days)] and following treatment with estrogen at midgestation (day 100), compared to levels at mid-gestation. Protein kinase C (PK-C) activity in both cytosolic and membrane-bound fractions was similar at mid- and late gestation and not altered by treatment with estradiol.; Secondly, we determined whether maturation of the fetal adrenal reflects enhanced expression of the mRNA for the ACTH precursor proopiomelanocortin (POMC). Pituitary POMC mRNA, was greater in baboon fetuses at term than at mid-gestation and increased on day 100 in estrogen-treated animals. Immunohistochemical studies confirmed that ACTH protein paralleled changes in POMC mRNA. Next, we determined whether the ontogenetic increase in POMC/ACTH in fetal baboon pituitaries reflected an increase in hypothalamic corticotropin-releasing hormone (CRH). CRH protein and CRH mRNA at mid-gestation were similar to concentrations in fetal baboons of late gestation and were not altered in fetuses in which the mother was treated with estradiol. In conclusion, the onset of fetal adrenal steroidogenic maturation normally near term and prematurely at mid-gestation following estrogen administration reflects increased expression of fetal pituitary POMC mRNA/ACTH protein and are not associated with a concomitant increase in hypothalamic CRH peptide or CRH mRNA.; Thirdly, since the 11β-hydroxysteroid dehydrogenase (11β-HSD)-catalyzed metabolism of maternal cortisol and cortisone by the placenta is an important component in the sequence of events regulating the function of the baboon fetal pituitary-adrenocortical axis, both baboon 11β-HSD-1 and -2 gene promoters were isolated and sequenced and shown to exhibit extensive homology to their respective human sequences. Both genes were subcloned into luciferase reporter vectors and transiently-transfected into human placental JEG-3 cells. In the presence of 17β-estradiol and estrogen receptor α, basal promoter activities of both 11β-HSD-1 and -2 increased 8-fold. Finally, RT-PCR analysis demonstrated a significant reduction of both 11β-HSD-1 and -2 mRNAs in baboon placental syncytiotrophoblast-enriched fractions following reduction of maternal serum estrogen in vivo by a highly-specific P450-aromatase enzyme inhibitor, CGS 20267.