P855

         J Appl Physiol 1989 Oct;67(4):1428-37

        Erratum in:

        J Appl Physiol 1990 Jan;68(1):following Table of Contents

        J Appl Physiol 1990 Jun;68(6):following 2701

        Reflex responses to capsaicin: intravenous, aerosol, and intratracheal

        administration.

        Palecek F, Sant'Ambrogio G, Sant'Ambrogio FB, Mathew OP.

        Department of Physiology and Biophysics, University of Texas Medical

        Branch, Galveston 77550.

        Intravenous capsaicin elicits the "pulmonary chemoreflex" (apnea,

        bradycardia, and hypotension) presumably through the stimulation of

        "pulmonary C-fibers." The present study was designed to ascertain

        whether tracheobronchial C-fibers play a role in the above reflex

        response. We compared the effects of capsaicin injected intravenously,

        administered as an aerosol, and administered topically into the

        intrathoracic trachea in anesthetized dogs (n = 17) and rats (n = 17).

        We measured esophageal, subglottic, and arterial pressures together with

        abdominal muscle electromyogram. Changes in expiratory duration [(TE),

        measured as the ratio TEtest to TEcontrol, mean  SD] due to capsaicin

        were similar with all three routes of administration in both dogs

        (intravenous, 7.9  4.6; aerosol, 5.5  3.1; topically into

        intrathoracic trachea, 7.1  4.8) and rats (intravenous, 22.6 

        10.3; aerosol, 11.1  8.2; topically into intrathoracic trachea, 21.6

         4.6). An increase in laryngeal resistance was a constant finding in

        the rat, but it was less frequent in the dog. Cardiovascular responses

        consisting of bradycardia and hypotension occurred with all three routes

        of administration but had longer delays than the respiratory responses.

        Capsaicin instillation into the extrathoracic trachea in dogs (n = 7)

        also induced qualitatively similar cardiorespiratory responses. We

        conclude that 1) capsaicin-sensitive receptors are accessible from both

        the pulmonary circulation and the airway lumen and 2) afferents, even in

        the extrapulmonary portion of the tracheobronchial tree, can play a role

        in the reflex responses to intraluminal capsaicin.