The Microbial Generation of Nitric Oxide in the Human Oral Cavity

Abstract

Nitric oxide a potent antimicrobial agent and vasodilator, may be synthesized in the human mouth due to the bacterial reduction of salivary nitrate. The purpose of this study was to determine whether intra-oral pH changes produced by the oral flora may augment the production of nitric oxide. To test this hypothesis a sucrose mouthrinse was administered to human volunteers who were free from caries and periodontal disease and production of oral nitric oxide was related to intra-oral pH changes. Baseline measurements consisted of pooled supragingival plaque and anterior and posterior tongue scrapings for microbiological analysis. Additional samples of saliva were collected for nitrate and nitrite analysis. Intra-oral pH measurements were recorded with a microelectrode at selected sites and NO intra-oral levels were measured by chemiluminescence. In addition selected members of the oral flora were tested for their ability to reduce nitrate to nitrite. A decrease in pH produced by the sucrose rinse was significantly associated with an increase in the intra-oral generation of NO after 5 min (p=0.006). The most frequently recovered nitrate reducing organisms were Veillonella spp. and Actinomyces spp. whilst the acidogenic Streptococcus spp. were negative nitrate reducers. The oral generation of NO appears to be influenced by pH levels within the oral cavity.