title: On the mechanism of guinea-pig tracheal relaxation induced by high histamine concentrations.
abstract: In concentrations higher than 1 X 10(-3)M histamine relaxed guinea-pig tracheal strips previously contracted by lower histamine concentrations. The blocker of H1-histaminergic receptors diphenhydramine (1 X 10(-6)M and 1 X 10(-5)M) and the alpha-adrenoblocker phentolamine (1 X 10(-5)M) potentiated histamine-induced relaxation. The beta-blocker propranolol (1 X 10(-4)M) decreased the histamine relaxant effect. Oxprenolol (1 X 10(-4)M) that is a less potent blocker of the tracheal beta 2-adrenoreceptors and is a partial beta-agonist did not influence histamine-induced relaxation. It is suggested that high histamine concentrations relax the guinea-pig tracheal strips by activating the H2-receptors and by depleting catecholamines in the smooth muscle.
mesh_terms: D000818:Animals; D006168:Guinea Pigs; D006632:Histamine / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009126:Muscle Relaxation / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D014132:Trachea / Q000502:physiology
chemical_list: D006632:Histamine