Effects of 3-methylhistamine and phenylethylamine on histamine action on isolated guinea-pig trachea rings

Abstract

It is well known that histamine produces constriction via H 1 receptors and decreases tracheal smooth muscle tone via H 2 and H 3 receptors. In addition, it has already been reported that 3-methylhistamine and phenylethylamine are competitive antagonists of histamine N-methyl-transferase (HMT), the enzyme responsible for rapid inactivation of histamine. Our results suggest the possibility that 3-methyl-histamine and phenylethylamine as competitive antagonists of histamine N-methyl-transferase lead to potentiation of histamine induced constriction of isiolated guinea-pig trachea, probably due to the decrease of histamine methylation and consequent inactivation. In as much, 3-methyl-histamine and phenylethylamine had no effect on the basal tone of isolated trachea smooth muscle, as well as on other mechanisms leading to increased responsiveness of guinea-pig tracheal smooth muscle (acetylcholine, KCl, electro stimulation).