Prostaglandin E-type receptor subtypes and gastroduodenal bicarbonate secretion in rats

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We investigated the relationship between prostaglandin E-type receptor (EP receptor) subtypes and gastroduodenal HCO3− secretion in rats. Under urethane anaesthesia, a stomach mounted in an ex vivo chamber or a proximal duodenal loop was perfused with saline and the HCO3− secretion was measured at pH 7.0 using a pH-stat method and by adding 10 mmol/L HCl. Prostaglandin E2 (PGE2, i.v.) increased HCO3− secretion in both the stomach and duodenum; this action was verapamil sensitive and only in the duodenum was potentiated by isobutylmethyl xanthine (IBMX). Duodenal HCO3− secretion was also stimulated by both sulprostone (EP1/EP3 agonist), enprostil (EP1/EP3 agonist), misoprostol (EP2/EP3 agonist), 11-deoxy PGE1 (EP3/EP4 agonist) and ONO-NT-012 (EP3 agonist), but was not affected by either butaprost (EP2 agonist) or 17-phenyl-ω-trinor-PGE2 (EP1 agonist). In contrast, gastric HCO3− secretion was stimulated by sulprostone, enprostil and 17-phenyl-ω-trinor-PGE2, but not by misoprostol, butaprost, 11-deoxy PGE1 or ONO-NT-012. The EP1 antagonist SC-51089 inhibited the HCO3− stimulatory action of sulprostone in the stomach but not in the duodenum. Isobutylmethyl xanthine potentiated the HCO3− response to sulprostone in the duodenum, while verapamil reduced the response in both the stomach and duodenum. These results suggest that PGE2 stimulates HCO3− secretion via different EP receptor subtypes in the stomach and duodenum: in the former the EP1 receptors linked to Ca2+ and in the latter, the EP3 receptors coupled with both cAMP and Ca2+.

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