A new study suggests that the body's production of nitric oxide (NO) in response to low oxygen levels could improve the recovery of critically ill patients in intensive care.

Researchers at University College London (UCL; United Kingdom) and the University of Warwick (United Kingdom) conducted a study that involved blood samples and results collected from 198 trekkers and 24 climbers (including doctors and scientists) that participated in the 2007 Caudwell Xtreme Everest (CXE) expedition. Using an integrated biochemical/whole-body physiology approach, the researchers were able to show that nitrite and nitrate--plasma biomarkers of NO production--and activity (cGMP) are elevated on acclimatization to high altitude, while S-nitrosothiols are initially consumed, suggesting multiple NOs contribute to improve hypoxia tolerance by enhancing NO availability.

The results suggest that NO is an integral part of the human physiological response to hypoxia, a finding that may be of relevance not only to healthy subjects exposed to high altitude, but also to patients in whom oxygen availability is limited by diseases affecting the heart, lung, or vasculature. The results also show that NO production and activity are elevated in people who live at near sea-level altitudes that ascend to altitude, leading to changes in blood flow in the smallest blood vessels. The results are also consistent with earlier data from residents of the Tibetan plateau, showing their normal NO levels to be much elevated compared to people living near sea-level. The study was published in the October 6, 2011, issue of Scientific Reports.

“By taking blood samples from hypoxic, but otherwise healthy, individuals we have been able to show that the body's natural response to low oxygen availability is to increase the production of nitric oxide,” said joint lead author Denny Levett, MD, of the UCL Center for Altitude, Space, and Extreme Environment Medicine. “Thus, elevated NO occurs not just in those who live at high altitudes permanently, but also in lowlanders who are trying to adapt to high altitude conditions.”

NO is a ubiquitous signaling molecule produced through the metabolism of L-arginine by nitric oxide synthases (NOS). Its formation is crucial for the control of blood pressure, blood flow, and other vital bodily functions; amongst these, it is an important antioxidant, and a regulator of intermediary metabolism and cellular energy production by mitochondria.

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