Interaction between histamine and dichloroisoproterenol, hexamethonium, pempidine, and diphenhydramine, in normal and reserpine-treated heart preparations.

Histamine stimulated the isolated auricles and heart of the guinea-pig. The effect was best seen in auricles which had been previously depressed by treatment with reserpine. Ganglionic blocking drugs (hexamethonium and pempidine), applied to auricles which had been previously treated with reserpine, abolished the diphasic effect of nicotine, but did not alter the response to histamine. Dichloroisoproterenol did not modify the stimulant action of histamine in isolated auricles, either before or after treatment with reserpine; nor did it alter the response of the isolated heart. Diphenhydramine reduced or blocked the stimulant action of histamine in auricles which had been previously treated with reserpine. The results support the hypothesis that histamine stimulates the myocardium by a direct action on specific receptors.