The effects of histamine and nitric oxide on the electrical field stimulated rat stomach fundus and ileum

SUMMARY Histamine effects gastrointestinal system by Hi, H2 and H3 receptors. In this study we have aimed to investigate the effects of histamine on the contractile responses of rat stomach fundus and ileum strips that have been evoked by electrical field stimulation. Both of electrical field stimulation-induced contractile responses of rat stomach fundus and ileum strips have been attenuated by H| and H2 antagonists pyrilamine and famotidine respectively.In these conditions stimulation of H3 receptors by R-(a)- Methylhistamin augmented the inhibition of the contractile responses but the blockade of H3 receptors by thioperamide attenuated the inhibition and consequently increased the contractions. Despite during the study Hi receptor blocker pyrilamine and H2 receptor blocker famotidine attenuated the electrical field stimulation induced contractile responses of rat stomach fundus and ileum strips; ranitidine another H2 receptor blocker augmented the contractions of the preparations that has been produced by electrical field stimulation. It has been suggested that this is a special situation related with ranitidine itself not with H2 receptor blockade. Because another H2 receptor blocker famotidine diminishes the electrical field stimulation-induced contractile responses of rat stomach fundus and ileum strips instead of increase. When pyrilamine combined with famotidine the inhibition of the contractile responses elicited by electrical field stimulation were maintaned. But combination of pyrilamine with ranitidine did no effect contractile responses so it has been proposed that pyrilamine and ranitidine antagonize the effect of each of them on the electrical field stimulation-induced contractile responses of rat stomach and fundus preparations. Then we have observed that in the presence of Hi receptor blocker pyrilamine or H2 receptor blocker famotidine or combination of both of them; a histamine H3 receptor blocker compound thioperamide increased the electrically-induced contractions of rat stomach and fundus preparations. Whereas in the presence of H2 receptor blocker ranitidine, because of increased contractility, thioperamide could not increase the contractile responses that elicited by electrical field stimulation. As it was observed in the pyrilamine+famotidine combination; thioperamide also increased the contractile responses of rat stomach fundus and ileum strips to the electrical field stimulation in the presence of pyrilamine+ranitidine combination. 61