Other Functions
Dietary nitrate is also an important source of nitric oxide in mammals. Green, leafy vegetables, and some root vegetables (such as beetroot) have high concentrations of nitrate. When eaten and absorbed into the bloodstream nitrate is concentrated in saliva (about 10 fold) and is reduced to nitrite on the surface of the tongue by a biofilm of commensal facultative anaerobic bacteria. This nitrite is swallowed and reacts with acid and reducing substances in the stomach (such as ascorbate) to produce high concentrations of nitric oxide. The purpose of this mechanism to create NO is thought to be both sterilization of swallowed food, to prevent food poisoning and to maintain gastric mucosal blood flow.
A similar mechanism is thought to protect the skin from fungal infections, where nitrate in sweat is reduced to nitrite by skin commensal organisms and then to NO on the slightly acidic skin surface. Alternatively, nitrite anions on sun-exposed skin may be photolyzed to free nitric oxide radicals by UVA in sunlight. This mechanism may elicit significant changes to the systemic blood circulation in humans and exploited for therapeutic purposes
Nitric oxide also acts on cardiac muscle to decrease contractility and heart rate. NO contributes to the regulation of cardiac contractility. Emerging evidence suggests that coronary artery disease (CAD) is related to defects in generation or action of NO. Reduced levels of exhaled NO have been associated with exposure to traffic related air pollution. The bacterium Deinococcus radiodurans can withstand extreme levels of radioactivity and other stresses. In 2009 it was reported that nitric oxide plays an important role in this bacteria's recovery from radiation exposure: the gas is required for division and proliferation after DNA damage has been repaired. A gene was described that increases nitric oxide production after UV radiation, and in the absence of this gene the bacteria were still able to repair DNA damage, but wouldn't grow.
Read more about this topic: Biological Functions Of Nitric Oxide
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