CAPSAICIN-ACTIVATED BRONCHIAL-INITIATED AND ALVEOLAR-INITIATED PATHWAYS REGULATING TRACHEAL CILIARY BEAT FREQUENCY

We questioned whether the prolonged stimulation of ciliary beat freque ncy (CBF) to a short exposure of low-dose capsaicin (Wong et al. J. Ap pl. Physiol. 68: 2574-2580, 1990) could be due to the activation of in direct pathways involving neural reflexes initiated independently in t he bronchi and alveoli. Tracheal CBF (CBFtr) was measured temporally i n anesthetized groups of 10 dogs by means of heterodyne-mode correlati on analysis laser light scattering. To elucidate the site of the affer ent neural stimulation and the efferent mediators affecting the ciliat ed epithelium, capsaicin (3 nM) aerosol was delivered for 4 min, eithe r predominantly to the bronchi or to the alveolar regions, with use of pulsed aerosol techniques. This resulted in 13 pg of bronchial (85%) and 10 pg of alveolar (96%) capsaicin deposited, which caused marked s timulation of CBFtr with maxima at 7 and 35 min, respectively. Prior a dministration of aerosolized indomethacin to the bronchi or aerosolize d cromolyn to the alveoli inhibited the bronchial and alveolar respons es, respectively. Prior administration of aerosolized hexamethonium to the tracheal lumen blocked the stimulatory CBFtr responses from both capsaicin challenges. Ipratropium or propranolol aerosols delivered to the tracheal lumen also inhibited these responses. It is proposed tha t these pathways comprise one set of sensitive mechanisms to ensure a prolonged stimulation of CBF to effect the removal of secretions and t he irritant from the lungs.