FIG. 1.

The nitrate-nitrite-NO axis. Dietary consumption of nitrates or nitrites leads to increased levels of each of these anions in the circulation. Nitrate is secreted in saliva at high concentrations and is converted to nitrite by commensal bacteria within the glands. Some nitrite is converted to NO within the low acidic environment of the stomach. The rest that is absorbed, then circulates, and can be converted to nitrite in tissues or blood by enzymes that possess nitrite reductase activity. The nitrite reductase activity of most of these enzymes is favored under conditions of hypoxia or low pH. NO, nitric oxide.