Role of vagal C-fiber afferents in the bronchomotor response to lactic acid in the newborn dog

Departments of Physiology, Paediatrics, and Anaesthesiology, Queen's University, Kingston, Ontario, Canada K7L 3N6 We addressed the hypothesis that vagal C-fiber afferents and cyclooxygenase products are the mechanisms responsible for lactic acid (LA)-induced bronchoconstriction in the newborn dog. Perineural capsaicin and indomethacin were used to block conduction of vagal C fibers and production of cyclooxygenase products, respectively. Perineural capsaicin eliminated (85%) the increase in lung resistance (R L; 45 ± 5.6%) due to capsaicin (25 µg/kg), whereas the increase in R L (54 ± 6.9%) due to LA (0.4 mmol/kg) was only inhibited by 37 ± 4.7% ( P