Modulation by histamine of peripheral vagal transmission in anesthetized mongrel dogs.

Intravenous infusion of histamine (6.0 microgram/kg/min) attenuated bradycardic responses to electrical stimulation of right vagus in anesthetized mongrel dogs. Similarily histamine also reduced reflexly mediated decreases in the heart rate to phenylephrine, while bradycardia induced by exogenous acetylcholine was not altered. This inhibitory action of histamine on responses to vagal stimulation could be antagonized by pretreatment with metiamide, an H2-receptor antagonist; but not by pyrilamine, and H1-receptor blocker. Metiamide significantly potentiated the negative chronotrophic effect of vagal stimulation. These results indicate that histamine could inhibit peripheral vagal transmission via a presynaptic action. The ability of histamine to alter vagal transmission may have physiological significance and play a role in histamine-induced tachycardia.