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Nitric Oxide Helps Humans
Adapt to High Altitudes
NEW YORK (Reuters Health) - People
living at extremely high altitudes produce higher concentrations
of a compound that facilitates oxygen flow throughout the body,
researchers report.
The compound, nitric oxide (NO), is produced in the lungs and
helps blood vessels to dilate, thereby allowing oxygen-carrying
blood to flow more freely. NO also boosts the oxygen-carrying
capacity of hemoglobin, a component of red blood cells.
The findings, which are based on information from people in Bolivia
and Tibet, shed light on how humans adapt to high altitudes, according
to Dr. Cynthia M. Beall from Case Western Reserve University in
Cleveland, Ohio, and colleagues.
``The similar responses of these two geographically separate
high-altitude populations underlines the importance of NO for
life under hypoxic stress,'' they write.
Hypoxia is a severe lack of oxygen that causes symptoms ranging
from mental confusion to a life-threatening swelling of the brain.
According to the findings in the November 22 issue of Nature,
people who live at very high altitudes adapt by producing more
NO than individuals living at sea level. The researchers measured
concentrations of NO exhaled by 105 healthy nonsmokers living
in Tibet at 4,200 meters above sea level, in 144 people living
in Bolivia at 3,900 meters above sea level, and in 33 people living
at sea level in the US.
The Tibetans were found to have more than twice the concentration
of NO that US citizens had. Similarly, the concentration of NO
exhaled by the Bolivians was 25% greater than concentrations exhaled
by US individuals.
``The functional advantage of high NO concentrations in the lungs
seems to be to offset ambient hypoxia by enhancing the uptake
of oxygen from the lungs, which presumably improves delivery of
oxygen to peripheral tissues,'' Beall and colleagues conclude.
SOURCE: Nature 2001;414:411-412.
Reference
Source 89
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