Hyperresponsiveness to Non-adrenergic, Non-cholinergic Vagal Stimulation Following Multiple Antigen Challenge in Guinea-pigs

Summary: The role of airway inflammation, induced by weekly antigen challenge, in the airway hyperresponsiveness to vagal (whole and NANC components) nerve stimulation and to neurotransmitters (acetylcholine and selective agonists for tachykinin NK1 and NK2 receptors) has been studied in the guinea-pig. Primarily, the time course (3, 7 and 14 days following the last challenge) of the effects of repeated aerosol antigen challenge on airway inflammation and bronchoalveolar fluid cellular composition was investigated. At 7 days following the last antigen challenge a maximal (as compared to 3 and 14 days) inflammatory response, in terms of a diffuse mild to marked infiltration of eosinophils, neutrophils and lymphocytes, was evident throughout pulmonary tissues. Only at this time some evidence of eosinophilia and neutropenia was detectable in BAL fluids. In these animals there was a normal bronchial responsiveness to iv administration of acetylcholine, selective synthetic agonists for the tachykinin NK2 receptors and capsaicin. On the other hand a remarkable airways hyperresponsiveness to iv administration of selective agonists for tachykinin NK1 receptors, as well as electrical stimulation of the vagal nerves (in presence and in absence of atropine), was detected. As a whole, these data indicate that at the peak of the inflammatory airway response following multiple antigen challenge there is a selective hyperresponsiveness to stimulation of vagal (mainly the non-adrenergic, non-cholinergic component) nerves associated with an increase in tachykinins (NK-1)-mediated bronchospasm.