The inhibitory effect of histamine on the motility of rat uterus in vivo.

The experiments concerned the effects of histamine and its analogs 4-methylhistamine and 2-pyridyl-ethylamine on the spontaneous activity of the estrogenized rat uterus in vivo. These agonists given intravenously inhibited uterine activity. Histamine and 4-methylhistamine, but not 2-pyridyl ethylamine, produced this effect in a dose-dependent manner. The ability of histamine to reduce uterine activity was lowered by pretreatment with reserpine, adrenalectomy or 6-hydroxydopamine. The effect of 4-methylhistamine also was reduced by reserpine or adrenalectomy. The inhibitory effect of 2-(2-pyridyl) ethylamine was completely abolished by reserpine or adrenalectomy. Cimetidine attenuated the residual inhibitory effect of histamine in reserpinized rats. These results suggest that the uterine inhibitory action of histamine and 4-methylhistamine is mediated through catecholamine release and direct stimulation of the H2-receptors. The effect of 2-(2-pyridyl) ethylamine is only mediated by release catecholamine.