The coronary chemoreflex evoked by intrapericardial nicotine has a
somatic component.
Pickar, Joel G.
Department of Anatomy and Physiology, College of Veterinary
Medicine, Kansas State University, Manhattan, KS 66506
APStracts 3:0364H, 1996.
Stimulation of vagally-innervated cardiac or pulmonary receptors
reflexly evokes depressor responses called the coronary chemoreflex
and pulmonary depressor reflex, respectively. The efferent arm of the
pulmonary depressor reflex contains a somatic component wherein
monosynaptic and polysynaptic muscle reflexes are attenuated. The
purpose of the present investigation was to determine whether the
efferent arm of the coronary chemoreflex also attenuates the
monosynaptic knee jerk reflex. Cardiac receptors were stimulated by
injecting nicotine and bradykinin into the pericardial sac of 15
chloralose-anesthetized (50mg/kg) cats. The knee jerk reflex was
elicited by tapping the patellar tendon intermittently.
Intrapericardial nicotine attenuated the knee jerk reflex by -26.2
+/-6.5%. The attenuation was mediated by the vagus nerves because
vagotomy abolished the nicotine-induced attenuation. Stimulation of
cardiac receptors evoked the attenuation because blockade using
intrapericardial procaine abolished the nicotine-induced attenuation.
On the other hand, intrapericardial bradykinin augmented the knee
jerk reflex by +17.5 +/-3.3%. The effect was not mediated by the
vagus nerves; vagotomy did not abolish the bradykinin-induced
augmentation. Changes in the knee jerk reflex were not correlated
with changes in blood pressure nor heart rate evoked by
intrapericardial nicotine or bradykinin. These findings demonstrate
that reflex somatomotor responses accompany the reflex autonomic
responses elicited by cardiac receptors. The somatic component of the
vagally-mediated coronary chemoreflex could contribute to the
fainting reaction associated with exertional syncope of aortic
stenosis and vasovagal syncope.
Received 7 May 1996; accepted in final form 14 August 1996.
APS Manuscript Number H409-6.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 19 September 1996