The combined increase in NO and blood flow levels resulted in double the amount of oxygen delivered to the capillary beds in the Tibetans arms.
The researchers hypothesize that Tibetans have a genetic mutation that allows high NO production. Genetic studies and comparable data on sea-level populations living at high altitude would be needed to test that hypothesis, said Beall.
During the study, the researchers also recognized another population difference: Tibetan women were found to have higher nitrite and lower nitrate levels than those of Tibetan men, whereas no gender differences were found in sea-level dwellers.
In this research, blood flow is determined by the length, number and width of the diameter of blood vessels. These numbers are determined partly by NO, which is a dilator of the vessels and prevents high blood pressure, which would result from increased blood flow in restricted blood vessels. NO also helps in the release of oxygen to tissues. NO reacts in the blood to produce nitrite, nitrate, nitrosothiol proteins and -nitrosyl hemoglobin, which can be used as indicators of NO production. To confirm the increases in NO, the researchers subjected the Tibetan samples to sensitive high performance liquid chromatography, where the results verified the 10-fold increase of NO in the blood.
This study continues to unravel the mysteries of high altitude adaption and follows Bealls 2001 study, published in Nature, on the NO levels in exhaled breath of Tibetans, which were found to be 25 percent greater than that of local Cleveland residents. There was also a related paper on NO and pulmonary blood flow in 2005 in the Journal of Applied Physiology. Brian Hoit of the department of medicine at the Case Western Reserve School of Medicine was the lead author on that paper.
|Contact: Susan Griffith|
Case Western Reserve University