Histamine receptors of airway smooth muscle of ferret and rat

Abstract

Ferret trachea and bronchus contract to carbachol greater than 5-HT greater than bradykinin (BK) greater than PGF2alpha greater than histamine greater than 2-methylhistamine (2-MeH: a specific H1-receptor agonist). Rat trachea is insensitive to the spasmogenic actions of histamine, 2-MeH, PGF2alpha, BK and 5-HT. Ferret trachea and bronchus and rat trachea (which were partially contracted to carbachol) relax to isoproterenol greater than PGE1 greater than E2 greater than 4-methyl-histamine (4-MeH: a specific H2-histamine receptor agonist). High doses of histamine also relax rat trachea. The contractions of ferret airways to 2-MeH coupled with the antagonism of histamine-induced contractions by mepyramine showed the presence of H1-histamine receptors in the trachea and bronchus of ferret. After H1-blockade, the relaxant responses to histamine on ferret bronchus and trachea, and rat trachea were not affecte by "specific" doses of burimamide, metiamide, and cimetidine (H2-receptor antagonists), indomethacin (PG-synthetase inhibitor) and propranolol (a beta-adrenoceptor blocker). These results appear to suggest the existence of an atypical histamine receptor subtype (i.e. not of the classical H1 or H2 type) in the airways of rat and ferret.