Evidence for a single glucocorticoid regulated pool of adrenocorticotropin in sheep anterior pituitary.

The goal of this study was to determine whether separate glucocorticoid-sensitive releasable pools of adrenocorticotropic hormone (ACTH) could be distinguished in sheep anterior pituitary cells. Isolated cells were cultured in serum-free medium containing 0-10 nM cortisol (F) for 7-11 days to determine whether variation in the glucocorticoid environment selectively affected ACTH release stimulated by corticotropin-releasing hormone (CRH) or arginine vasopressin (AVP). Secretion was studied using a microperifusion system. The results indicated that while the concentration of F in the medium bathing the cells profoundly influenced the magnitude of ACTH released in response to either peptide, the fractional release of total ACTH was unchanged. F concentration in culture medium similarly did not alter the negative-feedback effectiveness of a larger dose of F applied to cells 45 min before treatment with CRH or AVP. These results support the existence of a single glucocorticoid-sensitive pool of ACTH in corticotrophs.