AJP - Heart and Circulatory Physiology, Vol 256, Issue 2 486-H492, Copyright © 1989 by American Physiological Society
Vasopressin contributes to maintenance of arterial blood pressure in dehydrated baboons
K. L. Ryan, R. M. Thornton and D. W. Proppe
Department of Physiology, University of Texas Health Science Center, San Antonio.
This study primarily sought to determine whether the role of vasopressin
(VP) in maintenance of arterial blood pressure is enhanced in awake,
chronically instrumented baboons after 68-72 h of dehydration. This
question was approached by pharmacologically blocking vasopressin
V1-receptors in euhydrated and dehydrated baboons with or without a
normally functioning renin-angiotensin system (RAS). VP blockade during
dehydration produced a rapidly occurring (within 5 min), statistically
significant (P less than 0.05) decrease in mean arterial pressure (MAP) of
5 +/- 1 mmHg in the RAS-intact condition and an identical decline in MAP (5
+/- 1 mmHg) during blockade of the RAS by captopril, an angiotensin
I-converting enzyme inhibitor. At 15 min after induction of VP blockade,
heart rate was elevated by 9 +/- 2 beats/min in the RAS-intact condition
and by 20 +/- 5 beats/min in the RAS-blocked condition. In addition, VP
blockade in the dehydrated state produced small and equal increases in
hindlimb vascular conductance in RAS-intact and RAS-blocked conditions.
None of these cardiovascular changes were produced by VP blockade in the
euhydrated state. RAS blockade produced modest declines in MAP in both
hydration states, but the fall was larger by 7 +/- 4 mmHg in the dehydrated
state. Thus both VP and the RAS contribute to the maintenance of arterial
blood pressure during dehydration in the conscious baboon.
