title: Histamine tachyphylaxis in human airway smooth muscle. The role of H2-receptors and the bronchial epithelium.
abstract: The role of airway epithelium and H2-receptors in the development of histamine tachyphylaxis was studied using human isolated bronchial smooth muscle strips obtained from 18 patients undergoing thoracotomy. In epithelium-intact strips, a 38% reduction in the maximal contractile response (Emax) (p less than 0.002) and a 2.14-fold increase in the EC50 (p less than 0.02; n = 18) was observed after three separate histamine cumulative concentration effect curves (CCEC). In contrast, significant differences were not seen for either Emax (p greater than 0.4; n = 10) or EC50 (p greater than 0.26; n = 10) in epithelium-denuded strips. In separate experiments, both intact and denuded muscle strips were treated with the H2-receptor antagonist ranitidine (60 microM), either 30 min prior to the first or 30 min prior to the second histamine CCEC. In epithelium-intact strips, pretreatment with ranitidine caused a 1.8-fold increase in Emax in the initial CCEC (p less than 0.02), and both ranitidine schedules prevented tachyphylaxis (n = 8). In epithelium-denuded preparations, ranitidine did not enhance the responsiveness to histamine beyond that seen in untreated epithelium-denuded strips (n = 6). These data suggest that histamine-induced tachyphylaxis occurs in human airway smooth muscle and is mediated, at least in part, via H2-receptors resident on airway epithelium. In vivo, this may function as a protective mechanism, but damage to the epithelium and loss of H2-receptors may be significant in the development of histamine bronchial hyperreactivity as seen in asthma.
authors.affiliation: Department of Medicine, University of Western Australia, Perth.
authors.forename: D A
authors.initials: DA
authors.lastname: Knight
authors.forename: G A
authors.initials: GA
authors.lastname: Stewart
authors.forename: P J
authors.initials: PJ
authors.lastname: Thompson
mesh_terms: D001980:Bronchi / Q000187:drug effects / Q000502:physiology*; D004848:Epithelium / Q000502:physiology; D006632:Histamine / Q000494:pharmacology / Q000502:physiology*; D006801:Humans; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology; D011899:Ranitidine / Q000494:pharmacology; D011970:Receptors, Histamine H2 / Q000502:physiology*; D013618:Tachyphylaxis / Q000502:physiology*
chemical_list: D011970:Receptors, Histamine H2; D006632:Histamine; D011899:Ranitidine