Human saliva contained 4-hydroxyphenylacetic acid (HPA) (2-10 μM) and nitrite (60-300 μM). HPA was nitrated to 4-hydroxy-3-nitrophenylacetic acid (NO2HPA) when HPA and sodium nitrite were mixed at pH 1.0. NO2HPA was also formed when saliva was incubated under acidic conditions. These results suggest that salivary HPA is nitrated to NO2HPA when saliva is swallowed into the stomach. © 2002 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.
Takahama, U., Oniki, T., & Murata, H. (2002). The presence of 4-hydroxyphenylacetic acid in human saliva and the possibility of its nitration by salivary nitrite in the stomach. FEBS Letters, 518(1–3), 116–118. https://doi.org/10.1016/S0014-5793(02)02659-5