Roles of Nitric Oxide in the Formation of Acute Gastric Mucosal Lesions Induced by Water-Immersion-Restraint Stress in Rats

We examined the level of NOx and the expression of nitric oxide synthase (NOS) to determine the role of nitric oxide (NO) in the formation of acute gastric mucosal lesions induced by waterimmersion-restraint stress (WIRS) in rats. Male Wistar rats were used. Group A was subjected to WIRS (0, 5, 30, 60, 180, 360 min, n=5 per group). Group B consisted of rats given an intraperitoneal injection of L-arginine (100 mg/kg) 30 min before WIRS, which was applied as described for group A. The ulcer index was determined. In addition, the level of NOx in gastric tissue (Griess method), and the expression of NOS (eNOS, nNOS and iNOS) messenger RNA (mRNA) in gastric tissue (RT-PCR) were measured. The localization of NOS was studied by immunostaining. In group A, the ulcer index increased with time after WIRS. There were a decrease in the level of NOx and no increase in the expression of eNOS mRNA. In group B, no lesion was formed after 30 or 60 min, and the level of NOx and the expression of eNOS mRNA increased. There was no expression of iNOS mRNA in either group. No correlation was found between the expression of nNOS mRNA and ulcer index. The localization of eNOS was found in endothelial cells on immunostaining. These results suggest that a decrease in NO level and no increase in the expression of eNOS mRNA are associated with the formation of acute gastric mucosal lesions. Treatment with L-arginine increases the NO level and the expression of eNOS mRNA and inhibits the formation of acute gastric mucosal lesions, suggesting that NO derived from eNOS plays an important part in mucosal protection