THE ACTION OF HISTAMINE ON THE ISOLATED HEART.

A method is described for recording the coronary flow and the rate and the amplitude of contraction of an isolated heart maintained at constant temperature. Both histamine and noradrenaline increased the contractility of the guinea-pig heart. Pronethalol antagonized noradrenaline but not histamine. Mepyramine, 10-(2-pyrrolidin-1'-ylethyl)phenothiazine hydrochloride (pyrathiazine) and diphenhydramine reduced the contractility of the guinea-pig heart but did not antagonize the action of histamine. The influence of histamine and noradrenaline on coronary flow was variable but when the contractility of the heart increased there was a concomitant increase in coronary flow. Histamine decreased the contractility of the rat heart and the domestic fowl heart.