Tracheal responsiveness to histamine, PAF-acether and acetylcholine in normal and actively ovalbumin-sensitized guinea pigs.

The contractile effects of histamine (His), PAF-acether (PAF) and acetylcholine (Ach) were analyzed in tracheal rings from normal and ovalbumin-sensitized (OAS) guinea pigs. Although maximal responses to all agonists were enhanced in preparations from OAS guinea pigs, only the EC50 of Ach was significantly decreased. Previous treatment with 1 microM indomethacin (IND) or 10 microM quinacrine (QUIN) markedly displaced the dose-response curves for Ach on OAS preparations to the left, whereas the EC50 of His was only increased by QUIN. PAF-responses, however, were completely abolished by IND in preparations from both sensitized and unsensitized animals. These results indicate that ovalbumin sensitization significantly affects the tracheal response to Ach, His and PAF, an effect that appears to be mediated by arachidonic acid metabolites.