Department of Pediatrics, Division of Neonatology, Loma Linda University, Loma Linda, CA 92350, USA.
Nitric Oxide. 2012 Dec 1;27(4):193-200. doi: 10.1016/j.niox.2012.07.004. Epub 2012 Jul 26.
The salivary glands of adults concentrate nitrate from plasma into saliva where it is converted to nitrite by bacterial nitrate reductases. Nitrite can play a beneficial role in adult gastrointestinal and cardiovascular physiology. When nitrite is swallowed, some of it is converted to nitric oxide (NO) in the stomach and may then exert protective effects in the gastrointestinal tract and throughout the body. It has yet to be determined either when newborn infants acquire oral nitrate reducing bacteria or what the effects of antimicrobial therapy or premature birth may be on the bacterial processing of nitrate to nitrite. We measured nitrate and nitrite levels in the saliva of adults and both preterm and term human infants in the early weeks of life. We also measured oral bacterial reductase activity in the saliva of both infants and adults, and characterized the species of nitrate reducing bacteria present. Oral bacterial conversion of nitrate to nitrite in infants was either undetectable or markedly lower than the conversion rates of adults. No measurable reductase activity was found in infants within the first two weeks of life, despite the presence of oral nitrate reducing bacteria such as Actinomyces odontolyticus, Veillonella atypica, and Rothia mucilaginosa. We conclude that relatively little nitrite reaches the infant gastrointestinal tract due to the lack of oral bacterial nitrate reductase activity. Given the importance of the nitrate-nitrite-NO axis in adults, the lack of oral nitrate-reducing bacteria in infants may be relevant to the vulnerability of newborns to hypoxic stress and gastrointestinal tract pathologies.
成人的唾液腺将血浆中的硝酸盐浓缩到唾液中，然后由细菌硝酸盐还原酶将其转化为亚硝酸盐。亚硝酸盐在成人的胃肠道和心血管生理中可以发挥有益作用。当亚硝酸盐被吞下时，其中一些在胃中被转化为一氧化氮（NO），然后可能在胃肠道和全身发挥保护作用。目前尚不清楚新生儿何时获得口腔硝酸盐还原菌，或者抗微生物治疗或早产对硝酸盐转化为亚硝酸盐的细菌处理可能产生什么影响。我们测量了成人以及早产儿和足月婴儿在生命早期几周的唾液中的硝酸盐和亚硝酸盐水平。我们还测量了婴儿和成人唾液中的口腔细菌还原酶活性，并描述了存在的硝酸盐还原细菌的种类。婴儿口腔中将硝酸盐转化为亚硝酸盐的速度要么无法检测到，要么明显低于成人的转化速度。尽管存在口腔硝酸盐还原菌，如龋齿放线菌、非典型韦荣球菌和粘滑罗斯氏菌，但在生命的头两周内，婴儿的口腔中没有发现可测量的还原酶活性。我们得出结论，由于缺乏口腔细菌硝酸盐还原酶活性，相对较少的亚硝酸盐到达婴儿的胃肠道。鉴于硝酸盐-亚硝酸盐-NO 轴在成人中的重要性，婴儿口腔中缺乏硝酸盐还原菌可能与新生儿对缺氧应激和胃肠道病理的易感性有关。
