Fetal and Postnatal Development of the Adrenal Glands in Macaca mulatta

The inner four-fifths of the fetal and newborn adrenal cortex in Macaca mulatta morphologically resembles the human adrenal fetal zone. The human adrenal fetal zone is thought to undergo a dramatic collapse in the early postpartum period, whereas the inner zone of the rhesus fetal adrenal is slowly remodeled into definitive cortex. This remodeling is accompanied by a loss of one-third of the weight of the adrenals in the first 2 weeks postpartum and then by weight constancy for 6 months, after which growth is resumed. Near parturition, groups of small cells with little cytoplasm appear in the outermost rhesus fetal zone. In the early postpartum period, these groups coalesce into a "dense band" beneath the glomerulosa. This band is found progressively nearer the medulla during the early months of postnatal life, and the zona fasciculata appears peripheral to it. The cortical cells central to this band retain their fetal pattern; remnants of the fetal zone are still visible adjacent to the medulla 6 months after birth. Fetal hypophysectomy (decapitation) at midgestation or chronic administration of dexamethasone to the mother for several weeks during the third trimester caused hypoplasia of the fetal zone and precocious formation of a dense band and a zona fasciculata. Continuous infusion of ACTH into two fetuses resulted in hypertrophy of the fetal zone. Fetal adrenal weights were increased by ACTH (943 and 1149 mg, compared with 298 ± 27 mg for controls), but they were decreased by fetal decapitation or dexamethasone (46 ± 4 mg and 87 ± 13 mg, respectively). Thus, there is concordance between the histologically assessed magnitude of the fetal zone and the previously shown extent of fetal production of dehydroepiandrosterone sulfate and androstenedione, which are substrates for estrogen biosynthesis by the placenta. These data indicate that 1) the fetal zone is present until birth in M. mulatta , and it disappears slowly after birth, with no massive necrosis; and 2) the maintenance of fetal conformation of the adrenal glands depends on a functioning fetal pituitary gland. Normal evolution from a fetal to adult anatomical structure may be the consequence of a decreased circulating level of ACTH or a changing mode of response of the inner-zone cells to the trophic hormone.