Decreased expression of cytochrome P450 17 alpha-hydroxylase mRNA in senescent bovine adrenal gland.
To investigate the mechanisms of age-related decline in synthesis of adrenal androgen, we studied the contents of cortisol (F) and dehydroepiandrosterone (DHEA) and the amounts of cytochrome P450 17 alpha-hydroxylase (P450c17) mRNA and cytochrome P450 11 beta-hydroxylase (P450c11) mRNA in young (1 year old) and senescent (10-12 years old) bovine adrenal glands. We also examined effects of ACTH (10(-7) M) on the secretion of F and DHEA and on the induction of P450c17 and P450c11 mRNA expression in cultured adrenal cells from young and aged cows. The content of DHEA in adrenal glands and the secretion of DHEA in response to ACTH in cultured adrenal cells from senescent cow were lower than those from young cow, while the content and ACTH-stimulated secretion of F in senescent adrenals were of a similar level to those in young adrenals. The adrenal gland from aged cow showed a significantly lower level of P450c17 mRNA compared with young bovine adrenal. However, P450c11 mRNA was expressed in senescent adrenal glands at the same level as that in young adrenals. The induction of P450c17 mRNA by ACTH (10(-7) M for 24 h) in cultured adrenal cells from aged cow also showed a decline compared with that from young cow, although there was no difference the ACTH-induced accumulation of P450c11 mRNA in cultured adrenal cells between young and senescent cow. These results suggested that the expression of P450c17 mRNA decreased in aged bovine adrenal, which may cause the age-associated decline in biosynthesis of adrenal androgen.