EFFECTS OF EXTRAHYPOTHALAMIC DEXAMETHASONE IMPLANTS ON THE PITUITARY-ADRENAL SYSTEM

Abstract

ABSTRACT To study the possible involvement of extrahypothalamic regions of the brain in the negative feedback inhibition of corticotrophin (ACTH) secretion by corticoids, the effects of crystalline dexamethasone implants on compensatory adrenal hypertrophy (CAH) were investigated. Complete inhibition of CAH or actual adrenal atrophy followed implantation in a rather widespread field stretching from the anterior hypothalamus through the preoptic area to the septal and bordering regions. The effectiveness of implants in the septal-preoptic areas was not due to destruction of cerebral tissue, since electrolytic lesions in these regions had no significant effect on CAH. Although diffusion of the implanted steroid probably played some role in these results, they cannot be explained by simple diffusion to the hypothalamic median eminence, since implants just posterior or lateral to this area were generally ineffective. It was concluded that either (1) forebrain structures remote from the median eminence are sensitive to the negative feedback effects of corticosteroids, or (2) some unknown mechanism facilitates selective diffusion of implanted steroid from these regions to the basal hypothalamus, in preference to diffusion from other regions.