Effects of histamine on rat isolated atria

Abstract

The effects of histamine were studied in atria obtained from untreated and reserpine-pretreated rats. At high doses, histamine caused a positive chronotropic response that was not antagonized by either promethazine or cimetidine. In the presence of propranolol or in atria from reserpine-pretreated rats histamine caused an atropine-sensitive negative chronotropic response. Large doses of histamine also caused a positive inotropic response in left atria that were antagonized by the β adrenoceptor antagonist propranolol. Reserpine pretreatment abolished the inotropic response of histamine in the rat heart. The results indicate that in large doses histamine causes an indirect stimulation of β adrenoceptors (right and left atrium) by releasing endogenous noradrenaline and of muscarinic receptors (right atrium) by releasing acetylcholine.