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 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 caused a positive inotropic response in left atria that were antagonized by the .beta. adrenoceptor antagonist propranolol. Reserpine pretreatment abolished the inotropic response of histamine in the rat heart. In large doses histamine causes an indirect stimulation of .beta. adrenoceptors (right and left atrium) by releasing endogenous noradrenaline [norepinephrine] and of muscarinic receptors (right atrium) by releasing acetylcholine.