Fig 6.

Schema showing the pathways and interconversions of nitrite and nitrate. 1) Nitrate enters the mouth from diet and from the plasma by a concentrating action of the salivary glands. 2) In the mouth nitrate is converted to nitrite by commensal bacteria on the tongue [21]. 3) In the acid milieu of the stomach nitrite is converted to NO by disproportionation [11] or absorbed into the circulation. Nitrite may also be converted to NO in blood and tissues by the action of metalloproteinases [1]. NO can be converted to 4) nitrate by reaction with oxyhemoglobin [41] or 5) nitrite by ceruloplasmin [42].