Nonadrenergic Bronchodilation in Normal Subjects

Abstract

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 × 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 ( _30p) decreased over a 15-min period. Capsaicin induced significant bronchodilation; _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.