Studies on In Vivo Formation of Nitroso Compounds (IV)

The effects of dietary nitrate, pH and temperature on nitrate reduction in the human oral cavity

“…It is obvious that the greatest physiological activity of nitrite-producing bacteria of the oral cavity is at pH 8.0, indicating that they belong to neutrophiles [23]. Shown results are in agreement with many papers [10,17,19], which prove that the pH value of the greatest reduction activity of the oral cavity is between 7 and 8. It is assumed that the difference in results of cited papers is due to variation of saliva pH of different subjects.…”

“…Ingested nitrate is adsorbed from the stomach or intestines and about 25% is secreted in the saliva by anion transport system [4,5]. As a result, salivary nitrate concentrations are approximately 10 to 20 times those found in plasma [7,10]. Saliva collected directly from salivary ducts contains nitrate but no nitrite.…”

“…Saliva collected directly from salivary ducts contains nitrate but no nitrite. However, saliva collected at other locations in the oral cavity also contains nitrite [10]. Oral bacterial flora, mainly from the posterior surface of the tongue, reduce about 20% of salivary nitrate (5% of ingested nitrate) to nitrite, which is mostly swallowed in the saliva and is normally the main source of gastric nitrite [5,6].…”

The Noncanonical Pathway for In Vivo Nitric Oxide Generation: The Nitrate-Nitrite-Nitric Oxide Pathway

“…It was known at that time that bacteria existing in the lower GI tract (Salen, 1925;Zobell, 1932;Stieglitz and Palmer, 1936) could use nitrate as a terminal electron donor in respiration instead of oxygen and, thereby, reduce nitrate to nitrite (Moreno-Vivián et al, 1999;. In addition, consumption of nitrate and corresponding formation of nitrite in human saliva in vitro at 37°C had been shown to be prevented by heating the saliva to 100°C or by passing the saliva first through a filter (Goaz and Biswell, 1961;Ishiwata et al, 1975a). If the filter residue was returned to the saliva filtrate, the changes in salivary nitrate and nitrite levels were restored, suggesting a denaturable, biologic element in the residue fraction that was necessary for nitrate reduction (Goaz and Biswell, 1961;Ishiwata et al, 1975a).…”

“…In addition, consumption of nitrate and corresponding formation of nitrite in human saliva in vitro at 37°C had been shown to be prevented by heating the saliva to 100°C or by passing the saliva first through a filter (Goaz and Biswell, 1961;Ishiwata et al, 1975a). If the filter residue was returned to the saliva filtrate, the changes in salivary nitrate and nitrite levels were restored, suggesting a denaturable, biologic element in the residue fraction that was necessary for nitrate reduction (Goaz and Biswell, 1961;Ishiwata et al, 1975a). Further studies using commercially available antibacterial mouthwash or systemic antibiotics resulted in up to 90% reduction in salivary nitrite levels after an inorganic dietary load, supporting the view that bacterial conversion of nitrate was responsible for salivary nitrite (Tannenbaum et al, 1976;Dougall et al, 1995;Duncan et al, 1995).…”