Steroid Synthesis in Embryonic and Fetal Rat Adrenal Tissue

Abstract

Fetal and embryonic rat adrenal tissue was examined during gestation, particularly during the period of adrenal organogenesis, from the 12th through the 16th day of development. From the 12th day onward, the adrenal or adrenal-containing tissue produced dichloromethane-soluble acid-fluorogens in vitro at the same rate as adult glands. Much smaller quantities of lipid-soluble fluorogens were found in some incubates of younger embryos, whose tissues contained no visible adrenal blastemata. Corticosterone was found in incubates of 13 1/2 through 15 1/2 day tissue, but not in younger or older material (until the 19th day of development). The transitory period of corticosterone-secreting ability was marked by the presence of well-differentiated, polynucleolate adrenocortical cells, arranged in distinct nodules within the gland. Each nodule was covered by a layer of epithelial cells continuous with the poorly developed capsule. Adrenomedullary and large vascular elements were absent. Rapid adrenal growth and histological organization occurred after the 16th fetal day, accompanying the temporary lapse in corticosterone secretion. Neither total fluorogen nor corti-costerone secretion was stimulated in vitro by ACTH, regardless of the age of the fetal incubate. The results are discussed in terms of an early independence of adrenal development from pituitary control and a subsequent separation between the secretogogic and trophic components of ACTH activity. This separation is considered both as a possible difference between fetal and postnatal ACTH and as a consequence of the action of other fetal organs on the available fetal hormone.