PHENYLETHYLAMINE EFFECTS ON HISTAMINE-INDUCED CONTRACTION OF ISOLATED GUINEA-PIG TRACHEA RINGS

Summary: Histamine produces constriction of tracheal smooth muscle via H1 receptors, but it also decreases tracheal smooth muscle tone via H2 and H3 receptors. In addition, it has already been reported that phenylethylamine is competitive antagonist of histamine N-methyl-transferase (HMT), enzyme responsible for rapid inactivation of histamine. Our results suggest possibility that phenylethylamine as competitive antagonist of histamine N-methyl-transferase leads to potentiation of histamine induced constriction of isolated guinea-pig trachea, which could be consequence of decreased histamine methylation and subsequent histamine inactivation. At the same time, phenylethylamine had no direct effect on basal tone of intact isolated trachea rings, as well as on other mechanisms leading to increased responsiveness of guinea-pig tracheal smooth muscle (acetylcholine, KCl, electro stimulation).