Functional maturation of the primate fetal adrenal in vivo: 3. Specific zonal localization and developmental regulation of CYP21A2 (P450c21) and CYP11B1/CYP11B2 (P450c11/aldosterone synthase) lead to integrated concept of zonal and temporal steroid biosynthesis

Previous studies in the primate fetal adrenal gland have indicated that the gland is comprised of three functional zones: 1) the inner fetal zone (FZ), which has the enzymes necessary for dehydroepiandrosterone sulfate (DHEAS) production beginning early in gestation; 2) the transitional zone (TZ), which possesses enzymes necessary for cortisol production; and 3) the outer, definitive zone (DZ), which appears to function as a reservoir of progenitor cells that may populate the remainder of the gland and does not acquire a steroidogenic phenotype with the capacity to produce mineralocorticoids until near term. The enzymes CYP21A2 (P450 21 hydroxylase, or P450c21), CYP11B1 (11beta hydroxylase or P450c11) and CYP11B2 (aldosterone synthase) are necessary for glucocorticoid and mineralocorticoid synthesis but have not been localized previously in an ontogenic manner in the primate fetal adrenal gland. Therefore, we used immunocytochemistry (ICC) to assess specific zonal localization and developmental regulation of CYP21A2 and CYP11B1/CYP11B2 in the human (13-24 weeks' gestation) and rhesus monkey (109 d-term) fetal adrenal gland. In the fetal rhesus, ICC was performed with and without metyrapone administration to the fetus to assess the effects of endogenously increased fetal ACTH. In the human fetal adrenal, CYP21A2 immunoreactivity (IR) was present in only a few isolated cells in the DZ but was detectable in almost all cells in the TZ and FZ. In the fetal rhesus, CYP21A2-IR was present in cells throughout the DZ and TZ and, to a lesser degree, in the FZ. Staining intensity increased with advancing gestational age and was up-regulated in the DZ and TZ, but not the FZ, of the metyrapone-treated fetuses. In the human fetal adrenal gland, CYP11B1/CYP11B2-IR was absent in the DZ but present in the TZ and FZ. In the fetal rhesus monkey adrenal, CYP11B1/CYP11B2-IR was present in all cells of the TZ and FZ but was absent from the DZ until near term. After metyrapone, CYP11B1/CYP11B2-IR was induced in the DZ and was up-regulated in the TZ and FZ. Taken together, these data indicate that in the primate fetal adrenal gland, the FZ has the capacity to synthesize DHEA and DHEAS beginning early in development, the TZ has the capacity to synthesize cortisol after midgestation, and the DZ has the capacity to synthesize mineralocorticoids, but not until near term. The spatial localization of steroid metabolizing enzymes and steroid products in the human and rhesus monkey fetal adrenal suggests analogies of the three functional zones of the fetus (DZ, TZ, and FZ) to their adult counterparts (zona glomerulosa, zona fasciculata, and zona reticularis) and their steroid products (mineralocorticoids, glucocorticoids and androgens, respectively), although the reason for the presence of CYP11B1/CYP11B2- and CYP21A2-IR in the FZ remains to be elucidated.