The placenta as hypothalamus and pituitary: possible impact on maternal and fetal adrenal function.

The human placenta appears capable of providing trophic support for the maternal and fetal adrenal cortices. This effect could be mediated both directly, through placental secretion of ACTH1-39 and other peptides, and indirectly via placental CRH1-41 stimulation of pituitary ACTH1-39 secretion. Thus, the placenta is likely to influence the progressive changes that occur in the maternal HPA axis during pregnancy and to promote the developmental changes that occur in the fetal HPA axis. These effects are likely to be of particular importance near term, when the maternal and fetal HPA axes are maximally active and the fetus is dependent upon elevated glucocorticoid levels for maturation of organ systems. Finally, evidence from a variety of studies implicates placental CRH1-41 and ACTH1-39 in the cascade of events involving glucocorticoids and prostaglandins that culminates in parturition.