THE EFFECT OF INTRACAROTID VASOPRESSIN INFUSION ON ACTH RELEASE IN NEUROHYPOPHYSECTOMIZED, CONSCIOUS DOGS

Neurohypophysectomy (NHX) attenuates the adrenocorticotropic hormone ( ACTH) response to arterial hypotension but not corticotropin-releasing hormone (CRH) or insulin-induced hypoglycemia in conscious dogs. The purpose of the present study was to determine if increasing vasopressi n (AVP) in the cephalic circulation by carotid infusion normalizes the ACTH response to hypotension attenuated by NHX. Five male, conditione d dogs underwent controlled, acute decreases in arterial pressure (by similar to 25 mmHg) by infusion of sodium nitroprusside (NP) before an d > 4 wk after selective NHX. ACTH increased from 40 +/- 3 to 242 +/- 79 pg/ml during NP in the intact state. This response was greatly atte nuated after NHX (peak ACTH 81 +/- 15 pg/ml). Simultaneous intravenous infusion of AVP (12.5 ng/min) had a small, augmenting effect on the A CTH response to NP (peak ACTH 120 +/- 27 pg/ml). Intracarotid AVP (12. 5 ng/min) greatly augmented the ACTH response to NP (peak ACTH 202 +/- 26 pg/ml) such that it was no longer different from the intact respon se. Neither intravenous nor intracarotid AVP infusion per se had a gre at effect on ACTH. A normal ACTH response to hypotension requires an i ntact neurohypophysis and is mediated by a cephalic action of magnocel lular AVP.