The role of H1- and H2-receptors in the modulatory effects of histaminergic agents on adrenergic neurotransmission in rat vas deferens.

The role of the H1- and H2-receptors in the modulatory effects of histamine and other histaminergic drugs on smooth muscle adrenergic neurotransmission was studied on isolated preparations from rat vas deferens. The typical biphasic action (potentiation by low concentrations and inhibition by high concentrations) of histamine and some H1- or H2-agonists on vas deferens contractions induced by low frequency electrical stimulation (ES) was markedly changed by H1- or H2-antagonists. After blockade of H1-receptors, the potentiating effect of histamine and the histaminergic agonists was diminished or even reversed. The inhibition of the smooth muscle contractions by the drugs tested was stronger after H1-antagonists. Blockade of H2-receptors usually enhanced the potentiating effect of the histaminergic agonists on ES-evoked vas deferens contractions. The inhibitory action of histamine and the histaminergic agents tested was decreased or even reversed after H2-receptor blockade. These results confirm the presence of H1-excitatory and H2-inhibitory receptors whose activation or inhibition can modulate adrenergic neurotransmission in vas deferens.