Diminishing Corticotrope Capacity to Release ACTH During Sustained Stimulation: The Twenty-four Hours After Bilateral Adrenalectomy in the Rat¹

Abstract

Pituitaries were collected from rats at various intervals up to 72 hr after adrenalectomy. Their capacity to secrete ACTH in vitro in response to crude rat median eminence extract (MEE) or lyophilized rat hypothalamic extract (NIAMD HE-RP-1) was tested against that of pituitaries from control rats. Pituitaries obtained from rats 4, 8, 18 and 24 hr after adrenalectomy had a markedly decreased capacity to respond to these agents. Pituitary release of FSH in response to MEE was not affected 24 hr after adrenalectomy. The response range was narrowed 24 hr after adrenalectomy; however, when the ACTH released in response to low doses of HE was expressed as % increase above resting output, the sensitivity of pituitaries at all times after adrenalectomy was similar to that of the unoperated controls. The results suggest that the triphasic curve in plasma ACTH levels which is observed during the first 72 hr after adrenalectomy is due to alterations in the capacity of the anterior pituitary to secrete ACTH during sustained stimulation by CRF. (Endocrinology95: 65, 1974)