Alterations in intragastric nitrite and vitamin C levels during acid inhibitory therapy

Abstract

Most nitrite entering the healthy acid-secreting stomach is derived from dietary nitrate. The latter is absorbed from the small intestine, 25% then being secreted by the salivary glands into the mouth. Buccal organisms subsequently convert 20% of this nitrate to nitrite. When this nitrite is swallowed, the ascorbic acid in the acidic gastric juice reduces it to nitric oxide, which is absorbed by the mucosa. In the process, the ascorbic acid is oxidized to dehydroascorbic acid. When the intragastric pH is elevated by powerful anti-secretory agents, this gastric chemistry is profoundly modified. At a neutral pH, the swallowed nitrite does not react with ascorbic acid but accumulates in the stomach. The level of nitrite in the gastric juice during treatment with anti-secretory medication is particularly high after a nitrate-containing meal. Powerful anti-secretory medication also lowers the intragastric concentration of ascorbic acid and total vitamin C, probably because of the relative instability of the vitamin at a higher pH. These changes in the intragastric concentrations of nitrite and ascorbic acid are most marked in Helicobacter pylori -infected subjects on proton pump inhibitor therapy. It is recognized that an elevated nitrite-to-ascorbic acid ratio predisposes to the formation of potentially carcinogenic N -nitroso compounds. It is, however, unclear at present whether such compounds are formed within the human stomach.