Nitrate, Nitrite and Nitric Oxide in Gastric Mucosal Defense
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
The human stomach normally contains high levels of bioactive nitric oxide (NO). This NO derives from salivary nitrate (NO3-) that is converted to nitrite (NO2-) by oral bacteria and thereafter non-enzymatically reduced in the acidic gastric lumen to NO. Nitrate is a common component in vegetables, and after ingestion it is absorbed in the small intestine. Interestingly, circulating nitrate is then concentrated by the salivary glands. Hence, intake of nitrate-rich vegetables results in high levels of NO in the stomach. The physiological effects of the high concentration of NO gas normally present in the gastric lumen have been hitherto unknown, and the present investigations were therefore conducted to address this issue.
NO produced in the gastric lumen after nitrate ingestion increased gastric mucosal blood flow and the thickness of the firmly adherent mucus layer in the stomach. The blood flow and mucus layer are essential defense mechanisms that protect the mucosa from luminal acid and noxious agents. Nonsteroidal antiinflammatory drugs (NSAID) are commonly prescribed and effective drugs for treating pain and inflammation, but are associated with severe gastrointestinal side effects. We demonstrated that a nitrate-rich diet protects against NSAID-induced gastric damage, as a result of the increased formation of NO in the stomach. We also showed that the gastroprotective effect attributed to nitrate depended completely on conversion of nitrate to nitrite by the bacterial flora colonizing the tongue, and that the oral microflora is therefore important in regulating physiological conditions in the stomach.
In summary, this thesis challenges the current dogma that nitrate intake is hazardous, and on the contrary suggests that dietary nitrate plays a direct role in regulating gastric homeostasis. It is likely that a sufficient supply of nitrate in the diet together with the oral microflora is essential for preventing pathological conditions in the gastrointestinal tract.
Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2008. , 90 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 328
dietary nitrate, mucus gel layer, mucosal blood flow, mucus thickness, laser-Doppler flowmetry, mucosal damage, intra-vital microscopy, mucosal permeability
IdentifiersURN: urn:nbn:se:uu:diva-8624ISBN: 978-91-554-7152-1OAI: oai:DiVA.org:uu-8624DiVA: diva2:171763
2008-05-09, the main building of Uppsala University, Room IV, 13:15
Grisham, Matthew, Professor
Holm, Lena, ProfessorLundberg, Jon, ProfessorPhillipson, Mia, Assistant Professor
List of papers