The regulation and role of fetal adrenal development in human pregnancy

The rapid growth of the human fetal adrenal gland, which is primarily a ref lection of the growth of the unique fetal zone, is regulated by ACTH acting indirectly to stimulate the expression of locally produced growth factors, of which IGF-II and bFGF appear to play key roles. Through most of gestati on, the outer definitive zone appears to function as a reservoir of progeni tor cells which move centripetally to populate the rest of the gland. At th e end of pregnancy, the fetal zone undergoes senescence through an apoptoti c process. Activin and TGF-beta are capable of inducing apoptosis in the fe tal zone. Corticotropin-releasing hormone, which is produced by the placenta in marke dly increased amounts at the end of gestation, may orchestrate a variety of processes, including direct stimulation of fetal adrenal steroidogenesis, culminating in the initiation of parturition.