Area postrema-induced inhibition of the exercise pressor
reflex.
Bonigut, Stefanie, Ann C. Bonham, and Charles L. Stebbins.
Department of Internal Medicine, Division of Cardiovascular
Medicine and Department of Human Physiology, University of
California, Davis, Davis, California 95616
APStracts 3:0446H, 1996.
The exercise pressor reflex is opposed by the arterial baroreflex, and
circulating peptides may act in the area postrema to enhance this
inhibition. Therefore, we tested the hypothesis that the area
postrema exerts an inhibitory effect on this reflex. Consequently, in
6 [alpha]-chloralose anesthetized cats, blood pressure and heart rate
responses to 30 s of electrically stimulated hindlimb contraction
were compared before and after thermal coagulation of the area
postrema. In 6 other cats, the same contraction-induced
cardiovascular responses were assessed before and after chemical
lesion of the area postrema using kainic acid (214+/-9 nl, 2.5-5 mM).
Additionally, sinoaortic denervation (SAD) was performed (n=4) and
increases in blood pressure and heart rate in response to contraction
were then compared before and after systemic vasopressin (AVP) V1
receptor antagonism. Thermal lesion of the area postrema augmented
blood pressure and heart rate responses to contraction from 29+/-5 to
47+/-7 mmHg (P<0.05) and 8+/-2 to 14+/-2 beats/min
(P<0.05), respectively. Chemical lesion of the area postrema
enhanced contraction-evoked blood pressure (30+/-7 vs 47+/-6 mmHg,
P<0.05) and heart rate (12+/-4 vs 17+/-4 beats/min,
P<0.05) responses. Additionally, SAD abolished the
augmentation of the blood pressure response to contraction, which
previously has been shown to occur in response to systemic AVP V1
receptor blockade in intact cats. These data suggest that the area
postrema attenuates the exercise pressor reflex, possibly through the
actions of circulating peptides on baroreflex function.
Received 12 July 1996; accepted in final form 8 October 1996.
APS Manuscript Number H624-6.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996