Oxygen-dependence of ACTH-stimulated aldosterone and corticosterone synthesis in the rat adrenal cortex: Developmental aspects

Abstract

The control of ACTH-stimulated steroidogenesis under decreasing levels of O2 is not fully understood. The purpose of this study was to examine the effects of decreased O2 in vitro on rat adrenocortical steroid synthesis at different stages of development. Of interest was the evaluation of the effect of low O2 on steroidogenesis during the stress hyporesponsive period of the neonate. Rats were killed at 7, 14, or 42 days of age, adrenals collected and capsules (zona glomerulosa, ZG) separated from subcapsules (zona fasciculata/reticularis, ZFR). Cells were dispersed and placed into glass vials each gassed with a different level of O2 (21, 5, 2, 1, or 0% O2). The entire steroidogenic pathway was analyzed by measuring ACTH-stimulated cAMP, corticosterone and aldosterone production during a 2 h incubation. In addition, the early (P450 scc) and late (P450c11β and P450 aldo) pathway activities were examined in the presence of cyanoketone. The PO2 for half-maximal activity (P50) for aldosterone synthesis in ZG cells from 7- and 42-day-old rats was approximately 28 mmHg and 7 mmHg respectively, indicating that cells from older rats were more resistant to inhibition by low O2. The P50 for cAMP production from the ZG was ∼ 14 mmHg for both age groups. The P50 for corticosterone synthesis was ∼ 28 mmHg and < 7 mmHg in ZFR cells from 7- and 42-day-old cells respectively. The only enzyme activities affected by low O2 (< 35 mmHg) were P450 aldo and P450 scc. Moderate decreases in O2 (from ∼ 150 mmHg) decreased aldosteronogenesis, possibly due to observed decreases in cAMP generation, but not due to decreases in steroidogenic enzyme activity (7-day-old). Severe decreases in O2 presumably inhibited P450 aldo through a direct effect on enzyme activity (both ages). P450 scc activity (including cholesterol transport) also seems to be decreased by very low O2 (7-day-old). These findings illustrate a novel developmental alteration in O2-regulated steroid production, and may have implications for neonatal health and disease.