Nonadrenergic bronchodilation in normal subjects

To investigate whether bronchial C-fiber stimulation induced by capsaicin inhalation evokes nonadrenergic inhibitory (NAI) system bronchodilation, we studied partial and maximal expiratory flow-volume (PEFV and MEFV) curves in 5 normal subjects after inhalation of oxitropium bromide and propranolol. PGF(2α) (1 mg/ml inhaled for 5 min) was administered to induce bronchoconstriction. Then aerosolized capsaicin was inhaled (2.4 x 10^-9 mol) to stimulate bronchial C-fibers. PGF(2α) produced significant bronchoconstriction; FEV₁ and flow during a PEFV curve at 30% forced vital capacity (V̇(30p)) decreased over a 15-min period. Capsaicin induced significant bronchodilation; V̇(30p) increased for 2 to 6 min (0.001 < p < 0.02), and FEV₁ increased for 2 to 4 min (p < 0.05) when compared with saline-ethanol (vehicle of capsaicin) inhalation. After treatment with the ganglionic blocking agent hexamethonium, the significant bronchodilator response disappeared. These results suggest that the NAI system has a distinct bronchodilator action in human subjects in vivo, and that the bronchial C-fiber receptors may be involved in the reflex pathway for NAI system bronchodilation in humans.