Effects of aerosol antigen challenge in vivo on responsiveness of guinea pig tracheal and parenchymal strips in vitro to contractile agonists.

Guinea pigs sensitized to produce IgG-like antibodies were challenged with aerosol antigen in vivo. The following day responses in vitro to histamine and carbachol of tracheal and lung parenchymal strips (LPS) from challenged animals and unchallenged controls were compared. Responses of LPS to both histamine and carbachol were increased in challenged animals but tracheal strips from challenged guinea pigs did not display increased sensitivity to histamine or carbachol compared with controls. Moreover, the sensitivity of tracheal strips to carbachol decreased in challenged animals. The increased sensitivity of LPS from challenged animals may be due to the release of chemical mediators and down regulation of postsynaptic muscarinic receptors may account for the decreased sensitivity of tracheal strips.