AJP - Heart and Circulatory Physiology, Vol 271, Issue 5 1728-H1733, Copyright © 1996 by American Physiological Society
Cardiac output mediates the antihypertensive effect of vasopressin in spontaneous hypertension
S. Balakrishnan and J. R. McNeill
Department of Pharmacology, College of Medicine, University of Saskatchewan, Saskatoon, Canada.
The contribution of cardiac output and total peripheral resistance to the
fall in arterial pressure that follows cessation of a 3-h intravenous
infusion of arginine vasopressin (AVP; 20 ng.kg-1.min-1) was studied in
conscious spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats
instrumented with radiotelemetric probes for recording of blood pressure
and ultrasonic transit-time flow probes for measuring cardiac output.
Cessation of a 3-h infusion of AVP resulted in a significant decrease in
arterial pressure in SHR (14-17 mmHg below preinfusion control levels) but
not in WKY or in vehicle-treated controls. The fall in pressure persisted
for several days. The fall in pressure was associated with a large decrease
in cardiac output of 22 +/- 2 ml/min below control levels in SHR, and the
time course of the cardiac output response over several days approximated
the time course of the pressure response. By contrast, total peripheral
resistance remained elevated for some time on withdrawal of the AVP
infusion. We conclude that the withdrawal-induced antihypertensive
phenomenon in SHR is mediated by a fall in cardiac output and not by a
decline in total peripheral resistance.
