AJP - Regulatory, Integrative and Comparative Physiology, Vol 267, Issue 3 653-R658, Copyright © 1994 by American Physiological Society
The effect of intracarotid vasopressin infusion on ACTH release in neurohypophysectomized, conscious dogs
H. Raff, P. E. Papanek, J. F. Liard and A. W. Cowley Jr
Department of Physiology, Medical College of Wisconsin, Milwaukee 53226.
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 vasopressin (AVP) in the
cephalic circulation by carotid infusion normalizes the ACTH response to
hypotension attenuated by NHX. Five male, conditioned dogs underwent
controlled, acute decreases in arterial pressure (by approximately 25 mmHg)
by infusion of sodium nitroprusside (NP) before and > 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 attenuated after NHX (peak
ACTH 81 +/- 15 pg/ml). Simultaneous intravenous infusion of AVP (12.5
ng/min) had a small, augmenting effect on the ACTH 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 response. Neither intravenous nor
intracarotid AVP infusion per se had a great effect on ACTH. A normal ACTH
response to hypotension requires an intact neurohypophysis and is mediated
by a cephalic action of magnocellular AVP.
