Salivary contribution to exhaled nitric oxide

Abstract

Dietary and metabolic nitrate is distributed from the blood to the saliva by active uptake in the salivary glands, and is reduced to nitrite in the oral cavity by the action of certain bacteria. Since it has been reported that nitric oxide may be formed nonenzymatically from nitrite this study aimed to determine whether salivary nitrite could influence measurements of exhaled NO.Ten healthy subjects fasted overnight and ingested 400 mg potassium nitrate, equivalent to~200 g spinach. Exhaled NO and nasal NO were regularly measured with a chemiluminescence technique up to 3 h after the ingestion. Measurements of exhaled NO were performed with a single-breath procedure, standardized to a 20-s exhalation, at a flow of 0.15 L . s -1 , and oral pressure of 8±10 cmH 2 O. Values of NO were registered as NO release rate (pmol . s -1 ) during the plateau of exhalation.Exhaled NO increased steadily over time after nitrate load and a maximum was seen at 120 min (77.0 15.2 versus 31.2 3.0 pmol . s -1 , p<0.01), whereas no increase was detected in nasal NO levels. Salivary nitrite concentrations increased in parallel; at 120 min there was a four-fold increase compared with baseline (1.56 0.44 versus 0.37 0.09 mM, p<0.05). The nitrite-reducing conditions in the oral cavity were also manipulated by the use of different mouthwash procedures. The antibacterial agent chlorhexidine acetate (0.2%) decreased NO release by almost 50% (p<0.01) 90 min after nitrate loading and reduced the preload control levels by close to 30% (p<0.05). Sodium bicarbonate (10%) also reduced exhaled NO levels, but to a somewhat lesser extent than chlorhexidine acetate.In conclusion, salivary nitric oxide formation contributes to nitric oxide in exhaled air and a large intake of nitrate-rich foods before the investigation might be misinterpreted as an elevated inflammatory activity in the airways. This potential source of error and the means for avoiding it should be considered in the development of a future standardized method for measurements of exhaled nitric oxide. Eur Respir J 1999; 13: 327±333. In recent years there has been much interest in measurements of nitric oxide in exhaled air, since increased levels of NO were discovered in exhaled air of asthmatics [1] and enzymatically produced NO was suggested as a marker of inflammation in the respiratory tract [2,3]. However, several factors, such as mixing of NO originally produced in the paranasal sinuses, and variations in the degree of pressure and flow of the exhaled air, have been shown to influence and complicate the measurements [4]. These problems have created a need for a standardized method and a few articles have been published for methodological guidance [3,5]. Furthermore, a novel pathway of nonenzymatic NO production via chemical reduction of nitrite has recently been described [6,7] and this might complicate the methodological approach even further.A variable amount of nitrite, a potential substrate for NO formation, is found in the saliva as a product of nitrate reduction. Th...

Characterization of exhaled nitric oxide: introducing a new reproducible method for nasal nitric oxide measurements

“…The finding that a mouthwash procedure reduces oral contribution to the measurements of NO in orally exhaled air was expected and confirms the findings of ZETTERQUIST et al [17]. This, together with the reduction in methodological variation, indicates that elimination of oral NO would be preferable in future studies on orally exhaled NO.…”

“…Diurnal variation, with a rise in the NO levels in nasally and orally exhaled air over the day might be explained by dietary [17] as well as metabolic factors. A reduced level in the morning might be attributed to exercise (walking) [22], but the resting time allowed in this study should have ruled this out.…”

“…If we assume the contribution to levels of NO in nasally exhaled air from the fairly small region of the oropharynx with the posterior side of a lowered soft palate to be equal to the contribution to levels of NO in orally exhaled air from the oropharynx with the anterior side of an elevated soft palate. And, if it is assumed that the contribution from the lower airways from the hypopharynx and further down, to be equal when in nasally and orally exhaled air, and if, finally, it is assumed that the contribution from the oral cavity to be reduced tõ 0 after mouthwash [17], the contribution from the nasal cavity, paranasal sinuses and nasopharynx (supravelum space) equals NO in nasally exhaled air minus the levels of NO in orally exhaled air after mouthwash. Furthermore, it may be that nasal NO output is more dependent on airflow dynamics than the concentration gradient between luminal air and airway mucosa.…”

“…Using these methods the levels of NO in healthy human subjects in nasally and orally exhaled air was measured, to determine the normal biological variation in NO levels and variations due to errors of measurement. Finally, since it has been shown that there is a salivary contribution to orally exhaled NO [17], the effect of a mouthwash procedure on levels of nasally and orally exhaled NO was studied. All this, in order to examine the possibility of introducing an alternative method, where the level of orally exhaled NO is subtracted from nasally exhaled NO, to get a representative value of nasal NO.…”

Reference values of exhaled nitric oxide in healthy Asian children aged 5 to 18 years

“…However, other studies demonstrate different or no circadian FeNO patterns [30,37]. It has been established that there is increased FeNO after ingesting nitrate or nitrate-containing foods [38,39], while mouthwash procedures immediately before the measurement reduce such influence [38]. Thus, the rise in FeNO during the day may be attributed to dietary nitrate.…”