Pulmonary chemoreflexes elicited by intravenous injection of lactic
acid in anesthetized rats.
Lee, Lu-Yuan, Robert F. Morton, and Jan M. Lundberg.
Department of Physiology, University of Kentucky Medical Center,
Lexington, Kentucky 40536-0084, U.S.A. and Department of
Pharmacology, Karolinska Institute, Box 60400, S-104 01 Stockholm,
Sweden
APStracts 3:0456A, 1996.
Experiments were carried out to characterize the cardiorespiratory
reflex responses to intravenous injection of lactic acid and to
determine the involvement of vagal bronchopulmonary C-fiber afferents
in eliciting these responses in anesthetized rats. Bolus injection of
lactic acid (0.2 mmol/kg, i.v.) immediately elicited apnea,
bradycardia, and hypotension, which were then followed by a sustained
hyperpnea. The immediate apneic and bradycardiac responses to lactic
acid were completely abolished by bilateral vagotomy and were absent
when the same dose of lactic acid was injected into the left
ventricle. The subsequent hyperpneic response was substantially
attenuated by denervation of carotid body chemoreceptors. After a
perineural capsaicin treatment of both vagus nerves to block the
conduction of C-fibers, lactic acid no longer evoked the immediate
apnea and bradycardia, whereas the hyperpneic response became more
pronounced and sustained, presumably because of the removal of the
inhibitory effect on breathing mediated by pulmonary C-fiber
activation. Single-unit electrophysiological recording showed that
intravenous injection of lactic acid consistently evoked an abrupt
and intense burst of discharge from the vagal C-fiber afferent
endings in the lungs. In conclusion, the cardiorespiratory depressor
responses induced by lactic acid are predominantly elicited by
activation of vagal pulmonary C-fibers.
Received 18 April 1996; accepted in final form 22 July 1996.
APS Manuscript Number A374-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996