The following are excerpts from the paper, “The potential use of salivary nitrite as a marker of NO status in humans” (Source: ResearchGate)
Salivary nitrite as a marker of systemic NO availability
Understanding that the use of salivary nitrite as a marker of endogenous NO generation, both from oxidation of NO and from dietary sources, is totally dependent upon the uptake and excretion of nitrate by the salivary glands and subsequent reduction of nitrate to nitrite by lingual bacteria, there are steps in the pathway that become disrupted and lead to changes in salivary nitrite. Each step is described below:
i. Nitrate (from oxidation of NO or from diet) uptake in the salivary glands: It was recently reported that the sialic acid (SA)/ H+ cotransporter is involved in nitrate uptake into salivary glands .
ii. Nitrate secretion by salivary glands: The volumes of saliva produced vary depending on the type and intensity of stimulation, the largest volumes occurring with cholinergic stimulation.
iii. Oral bacterial nitrate reduction: Humans lack a functional nitrate reductase so salivary nitrate reduction is dependent upon oral commensal nitrate reducing bacteria.
iv. Oral pH: Healthy oral pH is between 6.5 and 7.5. The pKa of nitrite is 3.4 so any condition that lowers the pH in the oral cavity may destabilize nitrite and affect the use of salivary nitrite as a measure of NO activity.
Sampling saliva is simple, non-invasive and the concentration of nitrite in both plasma and saliva is an important biomarker for NO production/availability. This provides sufficient rationale for the use of salivary nitrite as a clinical test. It is still early, but further studies will show if it will be a useful tool in the clinical setting.