Studies on the glucocorticoid feedback control of acth secretion

Implants of cortisol acetate in the median eminence of intact rats depressed all measures of adrenocortical function compared with rats which had received cholesterol in the median eminence or an equal amount of cortisol acetate implanted in the cerebral cortex. Lesions in the median eminence of intact rats also depressed adrenocortical function. In contrast, neither implants of cortisol acetate nor lesions in the median eminence depressed adrenocortical function in hypophysectomized rats bearing 10 heterotopic pituitaries (H-T). A large dose of dexamethasone (100 µg/100 g) given systemically suppressed adrenocortical function in both intact and H-T rats. Additionally, implants of cortisol acetate in the median eminence were followed in 2 weeks by adrenal atrophy in intact rats, whereas the adrenal size of H-T rats was unaffected. These findings suggest that the median eminence does not play an important role in feedback control of heterotopic pituitary ACTH secretion. The median eminence may be of importance in feedback regulation of ACTH in intact rats only by virtue of its location at the origin of the pituitary stalk where the hypophyseal blood supply begins, rather than because of any specialized control it exerts on ACTH secretion.