Dietary nitrate is reduced to nitrite by some oral bacteria and the resulting nitrite is converted to nitric oxide (NO) in acidic gastric juice. The aim of this study is to elucidate the pathophysiological role of dietary nitrate in the stomach. Intragastric administration of nitrate rapidly increased nitrate and NO in plasma and the gastric headspace, respectively. Water-immersion-restraint stress (WIRS) increased myeloperoxidase (MPO) activity in gastric mucosa and induced hemorrhagic erosions by a nitrate-inhibitable mechanism. In animals that had received either cardiac ligation or oral treatment with povidone-iodine, a potent bactericidal agent, administration of nitrate failed to increase gastric levels of NO and to inhibit WIRS-induced mucosal injury. WIRS decreased gastric mucosal blood flow by a mechanism which was inhibited by administration of nitrate. These data suggested that the enterosalivary cycle of nitrate and related metabolites consisted of gastrointestinal absorption and salivary secretion of nitrate, its conversion to nitrite by oral bacteria and then to NO in the stomach might play important roles in the protection of gastric mucosa from hazardous stress.