Selective impairment of atrioventricular conduction by 2-(2-pyridyl)-ethylamine and 2-(2-thiazolyl)-ethylamine, two histamine H1-receptor agonists

Abstract To further characterize the receptor mediating histamine-induced impairment of atrioventricular conduction, the effects of two selective histamine H 1 -receptor agonists, 2-(2-pyridyl)-ethylamine (PEA) and 2-(2-thiazolyl)-ethylamine (ThEA), were investigated using the isolated guinea pig heart. These effects were compared with those of histamine and other selective agonists. PEA and ThEA produced a weak stimulation of cardiac rate and contractility; however, they produced a marked prolongation of atrioventricular conduction. The orders of relative potencies observed substantiate the hypothesis that H 2 -receptors mediate the positive inotropic and chronotropic effects and H 1 -receptors mediate the negative dromotropic effect of histamine.