Inhibition of sympathetic nervous system by histamine:studies with H1- and H2-receptor antagonists.

A study was designed to investigate the effect of histamine on sympathetic transmission to the myocardium in pentobarbital-anesthetized dogs. Intravenous infusion of histamine (1.0 and 2.0 microgram/kg/min) produced dose-related decreases in blood pressure and caused significant impairment of cardioacceleration observed during stimulation of the right postganglionic cardiac sympathetic nerve fibers. Positive chronotropic effects of intravenously administered norepinephrine as well as tyramine were not altered during histamine infusion. Blockade of neuronal reuptake with desipramine did not modify the inhibitory action of histamine on sympathetic nerve function. Prior administration of mepyramine (pyrilamine), a histamine type H1-receptor antagonist caused partial attenuation of the depressor action of histamine, but did not prevent histamine-induced inhibition of neurogenic function. Further treatment with metiamide, a histamine type H2-receptor antagonist caused nearly complete attenuation of the depressor response to histamine and also significantly antagonized the inhibitory action of histamine on sympathetic transmission to the myocardium. It is concluded that while the depressor action of histamine is due to the activation of both H1- as well as H2-receptors, histamine causes impairment of sympathetic nerve function to the myocardium by acting on H2-receptors which may be located on sympathetic nerve terminals.