Spasmolytic action of histamine in airway smooth muscle of horse.
Histamine, 2-methylhistamine (a specific H1-agonist), 5-HT, PGF2alpha, SRS-A, bradykinin (BK) and carbachol contract bronchial and tracheal smooth muscles of the horse. Isoprenaline, PGE1, E2, dimaprit and 4-methylhistamine (last two = specific H2-agonists) relaxed airways which were partially contracted to carbachol. Mepyramine (a specific H1-antagonist) selectively antagonized contractions to histamine. In the presence of mepyramine, histamine caused relaxation of airways partially contracted to carbachol. Metiamide and burimamide (specific H2-antagonists) specifically antagonized or reversed histamine-induced bronchorelaxation. However the H2-antagonists, indomethacin and propranolol each failed to block histamine-induced relaxations in trachea. Thus, the results of this study show: (i) preponderence of H1-receptors-mediating contractions in horse airways; (ii) presence of H2-receptors-mediating bronchorelaxation and (iii) the existence of an atypical (relaxant) response (resistance to H2-antagonists; indomethacin and propranolol) in the horse trachea.
D000818:Animals; D001285:Atropine / Q000494:pharmacology; D001980:Bronchi / Q000187:drug effects; D002049:Burimamide / Q000494:pharmacology; D002927:Cimetidine / Q000494:pharmacology; D006632:Histamine / Q000494:pharmacology*; D006736:Horses; D066298:In Vitro Techniques; D007213:Indomethacin / Q000494:pharmacology; D008785:Metiamide / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D011433:Propranolol / Q000494:pharmacology; D011738:Pyrilamine / Q000494:pharmacology; D012137:Respiratory System / Q000187:drug effects*; D014132:Trachea / Q000187:drug effects
D008785:Metiamide; D001285:Atropine; D002927:Cimetidine; D006632:Histamine; D011433:Propranolol; D011738:Pyrilamine; D002049:Burimamide; D007213:Indomethacin