Parasympathetic inhibition of sympathetic effects on sinus rate in
anesthetized dogs.
Furukawa, Yasuyuki, Yuji Hoyano, and Shigetoshi Chiba.
Department of Pharmacology, Shinshu University School of Medicine,
Matsumoto, Japan
APStracts 3:0012H, 1996.
The intracardiac parasympathetic neural elements that control sinus
rate are found in the fatty tissue overlying the atrial junctions of
the right pulmonary veins of the mammalian hearts. We refer to these
nerves as the sinus rate-related parasympathetic nerves (SRRPN).
Thus, to elucidate the role of SRRPN, we studied the effects of
cervical vagus stimulation on the positive chronotropic responses to
cardiac sympathetic nerve stimulation and isoproterenol infusion
before and after the SRRPN were removed in the open-chest
anesthetized dog heart. Before SRRPN denervation, cervical vagus
stimulation suppressed the sinus rate and the positive chronotropic
response to sympathetic nerve stimulation or isoproterenol infusion.
After SRRPN denervation, cervical vagus stimulation hardly decreased
the sinus rate. On the other hand, even after SRRPN denervation,
cervical vagus stimulation suppressed the rate increased by
sympathetic stimulation. Cervical vagus stimulation also attenuated
the sinus rate increased by isoproterenol. The inhibition by vagus
stimulation of the chronotropic response to sympathetic stimulation
was greater than that of the response to isoproterenol. The
attenuation by cervical vagus stimulation was abolished by atropine.
These results suggest that (1) a small number of the vagus nerves to
the SA nodal area different from the SRRPN decreases the sinus rate
increased by adrenergic interventions, and (2) the same activation
that causes relatively small effects on sinus rate are capable of
causing much larger changes in sinus rate during increased
sympathetic tone or in the case of [beta]-adrenoceptor agonists
treatment in the heart in situ.
Received 19 May 1995; accepted in final form 18 December 1995.
APS Manuscript Number H470-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 22 January 96