title: Antigen- and histamine H1 receptor-mediated relaxation of guinea pig isolated trachea.
abstract: We have investigated the effect of challenge in vitro with specific antigen (ovalbumin) on actively sensitized guinea pig tracheal rings maximally precontracted with methacholine. Ovalbumin relaxed the trachea in a concentration-dependent fashion with a negative log ED50 value (g/ml) of 7.0 +/- 0.3. In 16 experiments, the maximum antigen-induced relaxation was 26 +/- 3% of complete relaxation induced by 10(-3) M papaverine (mean +/- S.E.M.). Antigen-induced relaxations were selectively antagonized by diphenhydramine. Similarly, histamine relaxed the precontracted tracheal smooth muscle with a negative log molar ED50 of about 4.5 and a maximum effect of 28 +/- 3% (mean +/- S.E.M., n = 20). Histamine-induced relaxations were antagonized by diphenhydramine and mepyramine but were unaffected by cimetidine, metiamide or burimamide. Dimaprit (10(-5)-10(-3) M) did not relax the precontracted trachea. Indomethacin significantly inhibited relaxation induced by both antigen and histamine. In contrast, phenidone or 5,8,11,14-eicosa-tetraynoic acid had no effect on relaxation but reversed the inhibition by indomethacin. Neither propranolol (10(-6) M) nor removing the tracheal epithelium inhibited histamine-induced relaxation. These results suggest that antigen-induced relaxation of guinea pig tracheal smooth muscle involves activation of histamine H1 receptors and can occur independently of arachidonic acid metabolism, beta-adrenoceptor activation or airway epithelium.
mesh_terms: D000818:Animals; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000037:antagonists & inhibitors; D004848:Epithelium / Q000502:physiology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects; D009130:Muscle, Smooth / Q000502:physiology*; D010047:Ovalbumin / Q000494:pharmacology; D011946:Receptors, Antigen / Q000502:physiology*; D011968:Receptors, Histamine / Q000502:physiology*; D011969:Receptors, Histamine H1 / Q000502:physiology*; D014132:Trachea / Q000502:physiology
chemical_list: D001095:Arachidonic Acids; D011946:Receptors, Antigen; D011968:Receptors, Histamine; D011969:Receptors, Histamine H1; D016718:Arachidonic Acid; D010047:Ovalbumin