Involvement of NO-ergic neural pathway in reflex tracheal dilatation during bronchoconstriction in guinea pigs

The involvement of NOergic nerve in vagal reflex-mediated tracheal dilatation during bronchoconstriction was investigated using the guinea pig in vivo tracheo-bronchi separated preparation. Inhalation of 0.01% histamine to the bronchial site induced a biphasic, vagal reflex tracheal response, i.e., constriction followed by dilatation slightly after bronchial constriction. The reflex tracheal dilatation was inhibited by 49% by local treatment of the tracheal site with 1% propranolol. The residual dilatation in the presence of atropine and propranolol was significantly inhibited by 1% oxyhemoglobin or 1% carboxy-PTIO, NO scavengers. Cyclic GMP content in the tissue of the tracheal site during the reflex tracheal dilatation significantly increased. The increase in cyclic GMP was reduced by treatment of the tracheal site with 1% N omega-nitro-L-arginine methyl ester. These results support a hypothesis that reflex tracheal dilatation during bronchoconstriction may be mediated by not only adrenergic but also NOergic nerves in guinea pigs.