FEEDBACK SUPPRESSION OF NON-STRESS PITUITARY-ADRENAL FUNCTION IN RATS WITH FOREBRAIN REMOVED

The role of hypothalamic and extrahypothalamic structures in regulation of ‘non-stress' pituitary-adrenal function was assessed by measuring plasma corticosterone (Cpd B) concentrations 24 h following forebrain removal or brainstem transection. Morning (9 a.m.) ‘non-stress’ Cpd B levels were maintained within the normal range in basal hypothalamic island (BHI), pituitary island (PI), and brainstem-transected preparations and were significantly elevated in rats with large hypothalamic islands (HI). Anterior pituitary island preparations (API) had ‘non-stress’ Cpd B levels comparable to those of hypo-physectomized (Hypox) rats. Dexamethasone-21-P04 suppressed (P<0.01) ‘non-stress’ plasma Cpd B levels in HI, BHI, and PI preparations, suggesting that negative feedback acts in part directly on anterior pituitary. These findings corroborate those obtained with hypothalamic ‘deafferentation’ and suggest considerable autonomy from central neural connections for the hypothalamo-pituitary-adrenal system. © 1969 S. Karger AG, Basel.