A marked H1-receptor-mediated vasodilator effect of histamine in the isolated perfused rat heart.

Infusion of histamine into the coronary circulation of the isolated perfused rat heart produced a marked and concentration-dependent fall in perfusion pressure. A similar effect was obtained with 2-pyridylethylamine, a histamine H1-receptor agonist. Impromidine, a potent H2-receptor agonist, however, was found to be ineffective. Mepyramine but not cimetidine competitively inhibited the fall in perfusion pressure induced by histamine and 2-pyridylethylamine. Propranolol, a non-selective beta-adrenoceptor blocker, failed to abolish the coronary vasodilator effect of both histamine and 2-pyridylethylamine. From these results it was concluded that although the rat is known to be insensitive to histamine, this amine has a marked H1-mediated vasodilator effect in the isolated perfused coronary vasculature of this species.