Central integrative role of oestrogen in the regulation of placental steroidogenic maturation and the development of the fetal pituitary-adrenocortical axis in the baboon

The purpose of this review is to summarize the experimentaldata establishing the baboon as a non-human primate model forthe study of the endocrinology of human pregnancy, and to outlinethe results of in-vivo experiments in the baboon which showthat oestrogen plays a central integrative role in the regulationof placental steroidogenic maturation as well as the functionand maturation of the fetal adrenal gland. Thus, oestrogen regulatesthe receptor-mediated uptake of low-density lipoprotein-cholesteroland the P450 cholesterol side chain cleavage system within sycytiotrophoblaststo promote the production of progesterone. Oestrogen concomitantlyacts on the fetal adrenal gland to modulate the production ofandrogen precursors which ensures maintenance of physiologiclevels of oestrogen during the course of gestation. In addition,oestrogen regulates the 11ß-hydroxysteroid dehydrogenaseenzymes controlling placental cortisol-cortisone metabolismand their secretion into the fetal circulation and thus indirectlyregulates the fetal hypothalamic-pituitary-adrenocortical axis.Collectively, these oestrogen-regulated processes ensure themaintenance of pregnancy and the maturation of the fetus includingthe development in utero of adrenocortical self-sufficiencyessential for neonatal survival.