An outline of the biosynthesis of corticosteroids and androgens

Abstract

Early in human development steroid-producing cells appear; the first of these are the trophoblastic cells of the placenta. Although active in the production of progesterone and estrogens, the syncytiotrophoblast lacks several key enzymes in steroid metabolism and therefore the placenta is an incomplete steroidogenic tissue. The only cells able to synthesize glucocorticoids are those of the adult zone of the fetal adrenal cortex. The inner fetal zone of the adrenal cortex produces primarily dehydroepiandrosterone and its sulfate which can serve as precursors of estrone or estradiol-17β in the placenta. Estriol is formed in the placenta from 16-hydroxydehydroepiandrosterone, derived primarily from the fetus.The pattern of steroid metabolism in the human fetus and newborn is distinctly different from that of the adult, with a preponderance of 16-hydroxylated, Δ5-3β hydroxysulfurylated steroids in blood and urine. As gestation proceeds, the enzymes involved in cortisol synthesis increasé in activity. There is evidence that cortisol and the fetal adrenal play an important role in the onset of parturition in several species. The control of cortisol synthesis during intrauterine development probably involves ACTH, whereas dehydroepiandrosterone synthesis may be controlled by human chorionic gonadotrophin (HCG).