In vitro spontaneous and adrenocorticotropin-dependent maturation of the steroidogenic pathway of ovine fetal adrenal cells.

Adrenal cells from intact or hypophysectomized fetuses and newborn lambs cultured for 6 days under several conditions were tested for their ability to metabolize [14C]pregnenolone (P5) (5 X 10(-5) M) during a 2-h period. Also, their ability to produce P5 was investigated. At the beginning of the culture, the metabolism of P5 by adrenal cells from hypophysectomized fetuses was lower than that of cells from intact fetuses which in turn was lower than that of cells from newborns. After 6 days in culture in the absence of ACTH-(1-24), the metabolism of P5 by cells from both intact and hypophysectomized fetuses increase, whereas that of cells from newborns slightly decreases. Continuous ACTH-(1-24) (10(-8) M) treatment produced a striking increase in the capacity to metabolize P5 by cells from both intact and hypophysectomized fetuses and the maintainance of this capacity of cells from newborns was demonstrated. At the beginning of the culture the main product of [14C]P5 was corticosterone with cells from intact and hypophysectomized fetuses, and cortisol with newborn cells. After 6 days in culture in ACTH-free medium more than 50% of P5 added appeared as progesterone in all cases. Addition of ACTH-(1-24) to the culture medium induced within 5 days, a striking increase in the activation of 3 beta-hydroxysteroid dehydrogenase-isomerase, 17 alpha-, 21, and 11 beta-hydroxylases of adrenal cells from fetuses. However, the activity of 17 alpha-hydroxylase in adrenal cells from hypophysectomized fetuses was lower than that of cells from intact fetuses. ACTH-(1-24) treatment maintained the enzymatic activity of cultured newborn adrenal cells, except for 11 beta-hydroxylase which declined to about 50% of its activity on day 0. The capacity of fetal adrenal cells to produce P5 after acute ACTH-(1-24) stimulation increased 30-fold when cells were cultured in the absence of ACTH and up to 110-fold when cells were treated with ACTH-(1-24) from day 1 on. These results, together with those reported previously, show that the spontaneous in vitro maturation of fetal adrenal cell steroidogenic pathway is related to an increased activity of the 3 beta-hydroxylase dehydrogenase-isomerase and an enhanced capacity to produce P5. Both steps were stimulated further by ACTH. In addition, the hormone is an absolute requirement for the development and/or the maintenance of 17 alpha-hydroxylase activity.