Relaxant action of histamine on rabbit trachea: possible existence of third histamine receptor subtype.

The carbachol contracted rabbit trachea relaxes to isoproterenol, PGE1, E2, histamine and bradykinin. Histamine-induced relaxations were resistant to mepyramine (an H1-antagonist), burimamide, cimetidine, metiamide (H2-antagonists), propranolol (a beta-adrenoceptor blocker), indomethacin (a potent inhibitor of prostaglandin synthesis), trasylol (an inhibitor of kallikreins), aminophylline (a purinergic receptor blocker) and dibenzyline (a "D"-tryptamine receptor antagonist). The evidence achieved with these pharmacological agents appears to suggest that the chemical mediator responsible for the relaxant response to histamine is unlikely to be: catecholamines, prostaglandins, 5-HT, adenosine or ATP or kinins. The existence of H2-(iso or H3) histamine receptor subtype in rabbit trachea is postulated.