Role of vagal afferents in the reflex effects of capsaicin and lobeline inmonkeys

Reflex effects of pulmonary C-fiber receptor stimulation by tight atrial in jections of capsaicin and lobeline were investigated in conscious monkeys ( n = 17). Capsaicin injection (15.0 +/- 1.4 mug/kg) produced apnea mostly (n = 15, latency - 1.7 +/- 0.2 s) and bradycardia, which were abolished by va gotomy (n = 4). Lobeline administration (142 +/- 6 mug/kg) produced either apnea (n = 7, latency - 2.0 +/- 0.3 s) or excitation of breathing (n = 8, l atency - 3.5 +/- 0.3 s) and no change in heart rate. After vagotomy (n = 4) , the apneic response was abolished, but the respiratory excitation persist ed. Neither capsaicin nor lobeline produced cough. In the anesthetized monk ey also (n = 7), lobeline injection (50-150 mug/kg) did not produce any car diovascular response. However, it produced excitation of breathing, which p ersisted after vagotomy but was abolished by carotid sinus denervation. It is concluded that in the non-human primate, it is capsaicin that produces r eflexes typical of pulmonary C-fiber receptor stimulation, and cough is not a part of this reflex. (C) 2001 Elsevier Science B.V. All rights reserved.