Endogenous bradykinin in the thoracic spinal cord contributes to
the exercise pressor reflex.
Stebbins, Charles L., and Stefanie Bonigut.
Department of Internal Medicine, Division of Cardiovascular
Medicine and Department of Human Physiology, University of
California, Davis, Davis, California
APStracts 3:0264A, 1996.
This investigation tested the hypothesis that bradykinin causes
excitatory effects in the thoracic spinal cord that augment the
exercise pressor reflex. Thus, we performed 30 s of electrically
-stimulated static contraction of the hindlimb in the anesthetized cat
([alpha]-chloralose) to provoke reflex-induced increases in mean
arterial pressure, maximal left ventricular dP/dt, and heart rate
(i.e., the exercise pressor reflex). These three responses were
compared before and 15 min after intrathecal injection of 2 [mu]g
(n=3), 10 [mu]g (n=6) or 50 [mu]g (n=3) of the selective bradykinin
B2 receptor antagonist HOE 140 onto the thoracic spinal cord or 10
[mu]g of this antagonist on the lumbar (n=3) spinal cord. In 3 of the
6 cats in which 10 [mu]g of HOE 140 was injected onto the thoracic
spinal cord, an additional contraction was performed 60-90 min after
treatment. The 2 [mu]g dose of HOE 140 had no effect on the exercise
pressor reflex. Injection of 10 [mu]g of this antagonist onto the
thoracic spinal cord reduced the contraction-evoked pressor, maximal
dP/dt, and heart rate responses by 49+/-7, 58+/-4, and 64+/-13%,
respectively, (P<0.05), while 50 [mu]g of HOE 140 failed to
attenuate these responses further. In the 3 cats where an additional
contraction was performed 60-90 min after treatment with 10 [mu]g of
the antagonist, blood pressure and dP/dt responses had returned, in
part, toward initial values. Neither intravenous (n=3) nor
intrathecal injection of 10 [mu]g of HOE 140 onto the lumbar spinal
cord had any effect on the contraction-induced cardiovascular
responses. Thoracic injection of 50-200 ng of bradykinin provoked a
pressor response of 26+/-5 mmHg that was abolished by similar
injection of 10 [mu]g of HOE 14O. These data suggest that endogenous
bradykinin contributes to the exercise pressor reflex by an
excitatory action in the thoracic spinal cord.
Received 16 January 1996; accepted in final form 29 April 1996.
APS Manuscript Number A52-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 17 June 96