Lack of a role of adenosine in activation of ischemically sensitive
cardiac sympathetic afferents.
Pan, Hui-Lin, and John C. Longhurst.
Division of Cardiovascular Medicine, Departments of Internal
Medicine and Human Physiology, University of California, Davis,
Davis, California 95616
APStracts 2:0017H, 1995.
Adenosine has been implicated in the pathogenesis of cardiac pain
through activation of cardiac sympathetic afferents. The present
study was performed to assess directly the contribution of adenosine
in activating of ischemically sensitive cardiac sympathetic
afferents. Single-unit activity of ischemically sensitive afferents
located in either ventricles was recorded from the left thoracic
sympathetic chain or rami communicantes of anesthetized cats during 5
min of myocardial ischemia. Intracardiac injection (5 mg) or
epicardial application (1-5 mg/ml) of adenosine onto the receptive
fields failed to activate 31 ischemically sensitive A[delta]- and C-fiber
afferents, which were responsive to topical application of bradykinin
(10 _g/ml). Intracardiac injection (5 mg) or topical application (1-5
mg/ml) of an adenosine A1 receptor agonist, N6-cyclopentyladenosine,
also did not increase the discharge activity of 13 other ischemically
sensitive C-fiber afferents. Treatment with dipyridamole (1 mg/kg,
iv) to inhibit the cellular uptake of adenosine did not significantly
potentiate the response of 10 separate C-fiber afferents to 5 min of
myocardial ischemia. Furthermore, blockade of adenosine receptors
with aminophylline (5 mg/kg, iv) did not significantly attenuate the
response of 10 other C-fiber afferents to 5 min of myocardial
ischemia. The results of the present study demonstrate that exogenous
as well as endogenous adenosine do not contribute to activation of
ischemically sensitive cardiac sympathetic afferents. The findings of
the present study fail to support a substantial role for adenosine
and its A1 receptors in activation of cardiac sympathetic afferents
during myocardial ischemia.
Received 9 November 1994; accepted in final form 3 January 1995.
APS Manuscript Number H999-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 24 February 1995.