Reflex control of vasopressin during hemorrhage in hypertensive
rabbits.
Courneya, C. A., and G. Weichert.
Department of Physiology, University of British Columbia, Vancouver
B.C. V6T 1Z3
APStracts 2:0257H, 1995.
Hypertensive (HT) rabbits have impaired reflex control of heart rate
and vascular tone, which is, at least in part, related to
dysfunctional baroreceptors. We hypothesized that reflex control of
vasopressin (AVP) would also be impaired in the HT rabbit. To test
this we compared hemorrhage-induced increases in AVP between
conscious normotensive (NT) and HT rabbits. The hemorrhage-induced
rise in AVP was found to be significantly (P<0.05) attenuated in
the HT rabbits. We tested a 2nd hypothesis, that the observed
impairment was related to arterial baroreceptor function, by
hemorrhaging the same rabbits after reversible cardiac denervation.
Under these conditions only the arterial baroreceptors would be
expected to contribute to reflex control of AVP. Impairment was still
evident after cardiac denervation. That is, the hemorrhage induced
rise in AVP was significantly (P<0.01) attenuated in the cardiac
denervated, HT rabbits compared to NT rabbits. Thus impairment was,
at least in part, related to arterial baroreceptors. Previously we
showed in NT rabbits, that AVP only contributed to maintenance of
arterial pressure (during hemorrhage), after the Autonomic Nervous
System (ANS) had been blocked. Thus, in the present study, we
compared the maintenance of arterial pressure during hemorrhage,
between NT and HT rabbits after ANS blockade. Blood pressure
maintenance was significantly attenuated in the HT rabbits
(P<0.05). In addition, for a given fall in pressure,
significantly less AVP (P<0.05) was released in the ANS blocked,
HT rabbits as compared to NT rabbits. We concluded that the
attenuated ability to maintain arterial pressure during hemorrhage,
in the ANS blocked HT rabbits, was in part, due to the impairment in
reflex control of AVP.
Received 10 January 1995; accepted in final form 25 May 1995.
APS Manuscript Number H25-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 July 1995.