We examined the roles of cyclooxygenase (COX) isozymes, prostaglandins (PGs), and their receptors in the mucosal defense against ischemia/reperfusion (I/R)-induced gastric lesions in mice. Male C57BL/6 mice, including wild-type animals and those lacking prostaglandin E 2 (EP)1, EP3, or prostaglandin I 2 (IP) receptors, were used after 18 h of fasting. Under urethane anesthesia, the celiac artery was clamped (ischemia) for 30 min, and then reperfusion was achieved for 60 min through the removal of the clamp, and the stomach was examined for lesions. I/R produced hemorrhagic gastric lesions in wild-type mice. The severity of lesions was significantly increased by pretreatment with indomethacin (a nonselective COX inhibitor) and rofecoxib (a selective COX-2 inhibitor) but not 5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-(trifluoromethyl)-1H-pyrazole (SC-560; a selective COX-1 inhibitor). The expression of COX-2 mRNA was up-regulated in the stomach following I/R but not by sham operation or ischemia alone. The ulcerogenic response was markedly aggravated in IP receptor knockout mice but not those lacking EP1 or EP3 receptors. I/R increased the levels of 6-keto-PGF 1␣ and PGE 2 in the stomach of wildtype mice, and this response was attenuated by indomethacin and rofecoxib but not SC-560. Pretreatment of wild-type mice with iloprost, a prostacyclin (PGI 2 ) analog, significantly prevented the I/R-induced gastric lesions in the absence and presence of indomethacin or rofecoxib. PGE 2 also reduced the severity of I/R-induced gastric lesions, yet the effect was much less pronounced than that of iloprost. These results suggest that endogenous PGs derived from COX-2 play a crucial role in gastric mucosal defense during I/R, and this action is mainly mediated by PGI 2 through the activation of IP receptors.

Aim: We investigated the roles of NO/NOS isoforms in the pathogenesis of ischemia/reperfusion (I/R)-induced gastric injury in mouse stomachs. Methods: Under urethane anesthesia, the celiac artery was clamped, and then reperfusion was established 30 min later by removal of the clamp. After a 60-min reperfusion, the stomach was examined for macroscopic lesions. Results: Following I/R, hemorrhagic lesions were generated in the mucosa, although ischemia alone caused no visible damage. Prior administration of L-NAME (a nonselective NOS inhibitor) significantly aggravated these lesions, in a L-arginine-inhibitable manner. By contrast, the selective iNOS inhibitor 1400W significantly prevented the occurrence of I/R-induced gastric lesions. The mucosal MPO activity was increased after I/R, and this response was enhanced and attenuated by prior administration of L-NAME and 1400W, respectively. Interestingly, the later treatment with L-NAME, given 10 min before reperfusion, significantly reduced the severity of the I/R-induced gastric damage, in a L-arginine-dependent manner. The expression of iNOS mRNA was up-regulated in the stomach following I/R, with an increase of mucosal NO content, and the NO production was significantly inhibited by both L-NAME and 1400W. Conclusion: Endogenous NO plays a dual role in the pathogenesis of IR-induced gastric damage; NO/cNOS is protective while NO/iNOS is proulcerogenic during I/R.

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We investigated the roles of prostaglandin (PG) E₂ and cyclooxygenase (COX) isoenzymes in the mucosal defense of the esophagus, using subtype-selective EP agonists and antagonists as well as various COX inhibitors, in an acute rat esophagitis model. The animals were used after fasting for 18 h. Acid reflux esophagitis was induced by ligating both the pylorus and the transitional region between the forestomach and the glandular portion under ether anesthesia, and the damage was examined 3 or 4 h later. The esophageal lesions were significantly aggravated by prior administration of indomethacin and SC-560 (a selective COX-1 inhibitor) but not rofecoxib (a selective COX-2 inhibitor). PGE₂ prevented these lesions at lower doses, yet the protective effect disappeared at a high dose. This biphasic effect was mimicked by 17-phenyl PGE₂ (EP1 agonist) and antagonized by ONO-AE-829 (EP1 antagonist), while neither EP2, EP3, nor EP4 agonists had any effect on the esophageal lesions. PGE₂ and 17-phenyl PGE₂ had no effect on the acid secretion, but significantly increased the pepsin secretion, in a dose-dependent manner. The development of the esophageal lesions was totally prevented by pepstatin, a specific inhibitor of pepsin, and markedly aggravated by exogenous pepsin. We conclude that endogenous PGs derived from COX-1 are involved in the mucosal defense of the esophagus and that PGE₂ has a biphasic influence on esophageal injury, depending on the dose: a protective effect at low doses and a deleterious effect at high doses, both mediated by EP1 receptors – the latter effect of PGE₂ may be brought about by stimulation of the pepsin secretion.

We compared the HCO3(-) secretory response to capsaicin and mucosal acidification in rat duodenums, especially the relation to vanilloid receptor type 1 (VR1). 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 mM HCl. The secretion was stimulated by exposing the loop to capsaicin (0.03-0.3 mg/ml) or 10 mM HCl for 10 min. Indomethacin subcutaneously or ruthenium red intravenously, a nonspecific VR1 antagonist, was given 60 or 10 min, respectively, before exposure to capsaicin or acid, while L-NAME was given intravenously 3 hr before these treatments. Capsazepine, another VR1 antagonist, was coapplied to the loop for 10 min with capsaicin or acid. Luminal application of capsaicin increased the secretion of HCO3(-) in a dose-dependent manner; this effect was markedly attenuated by chemical ablation of capsaicin-sensitive afferent neurons (CSN) as well as pretreatment with ruthenium red or capsazepine, and significantly mitigated by indomethacin or L-NAME (in an L-arginine-sensitive manner). The HCO3(-) secretion was also stimulated by mucosal acidification, and this response was attenuated by both capsaicin pretreatment, indomethacin and L-NAME, but not ruthenium red or capsazepine. Mucosal application of capsaicin as well as acid increased the mucosal PGE2 content, and these effects were both significantly attenuated by indomethacin and L-NAME. These results suggest that both capsaicin and acid cause the CSN-dependent increase in duodenal HCO3(-) secretion mediated by NO and PG, yet the mode of their action differs in terms of the ruthenium red or capsazepine sensitivity. Although luminal H+ plays a modulatory role in duodenal HCO3(-) secretion, it is unlikely that the action results from the interaction of H+ with the ruthenium red- or capsazepine-sensitive site of VR1.