Abstract
In humans and other mammals, about one-quarter of all circulating inorganic nitrate (NO3−), derived from diet or oxidation of endogenous nitric oxide (NO), is actively taken up by the salivary glands and excreted in saliva (1, 2). As a result, salivary nitrate levels are 10–20 times higher than those levels found in plasma (3). The mechanism behind this massive nitrate accumulation in saliva has remained elusive. In PNAS, the work by Qin et al. (4) reports that the protein sialin can function as an effective nitrate transporter. These results are of considerable interest, especially in light of recent research suggesting a role for salivary nitrate transport and metabolism in physiological regulation of systemic NO homeostasis (5, 6).
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