Figure 1. Circulation of nitrate in the body.
The recycling of dietary nitrate is mainly in salivary glands, where sialin plays a key role in active transport and concentration of nitrate. Part of the nitrate is converted to nitrite by oral bacteria and subsequently absorbed in the stomach and intestine. Nearly 25% of circulating nitrate is reabsorbed by the salivary glands, whereas the majority is excreted by the kidneys. Nitrate performs physiological functions through the exogenous NO3--NO2--NO pathway. NO, nitric oxide; NO2-, nitrite; NO3-, nitrate.