Inhibition of electrically evoked contractions of guinea-pig ileum preparations mediated by the histamine H3 receptor.

We investigated the contraction responses of isolated guinea-pig ileum preparations under several conditions of electrical field stimulation. Histamine H3-agonists caused a dose-dependent inhibition of both cholinergic and nonadrenergic noncholinergic (NANC) responses (pD2 of histamine, 7.3; N alpha-methylhistamine, 8.4; (R)-alpha-methylhistamine, 8.3); H3-antagonists blocked this inhibition (pA2 of impromidine, 7.2; thioperamide, 8.5). Our results indicate that H3-receptors are present on both cholinergic and NANC nerves in the myenteric plexus and that the preparation can be used as a rapid and simple test system for histamine H3-receptors.