High altitude adaptation, viagra, and you

| Pharma Sports
I've written before about Cynthia Beall's work on oxygen adaptation. This week's Science has a short article with some more information about the biochemistry behind it:
But exactly how do these women manage to carry extra oxygen in their blood? They do not produce more hemoglobin the way Andeans living at high altitude do. One possibility is that the women with high oxygen have an adaptation that Beall is exploring independently in these same Tibetan villagers. She found that some villagers exhale extra nitric oxide in their breath, a sign of additional amounts of the gas in their blood. In those Tibetans, nitric oxide dilates the blood vessels so they can pump more blood and oxygen to organs and tissues, as measured by images of heart and lung blood vessels. The Tibetans can boost their blood volume--and so pump more oxygen to their tissues--without producing more hemoglobin or raising the blood pressure in their lungs. That's the reverse of what happens when mountaineers suffer from oxygen deficiency: The blood pressure in their lungs rises, the blood vessels constrict, and fluid builds up, suffocating the lungs.

The next step, says Beall, is to try to see whether these two lines of research meet. She wants to find the underlying gene behind the women's high-oxygen blood--and see whether it is related to genes that regulate levels of nitric oxide in the blood. She notes, however, that it's quite possible that the Tibetans have evolved more than one way to boost blood oxygen, and that these are independent adaptations. Gladwin suggests that Beall's team also measure nitric oxide and blood pressure in the lungs in pregnant women, who are under the most physiological stress at altitude and presumably would benefit most from this adaptation. "Study the pregnant women," he says, "because that's where you'll see evolution in action."

I wish I knew more about oxygen metabolism at high altitude, but a brief lit search seems to support the nitric oxide connection, in particular that there's some evidence that low nitric oxide levels make you susceptible to high altitude pulmonary edema (HAPE), as well as that you can use nitric oxide to treat HAPE. Given this, it's not too surprising that Viagra, which also operates via nitric oxide, appears to improves high altitude exercise performance for some people. Interestingly, in both treatment studies, one group of people responded and one did not, reinforcing the genetic variation in nitric oxide response theory.

One of the notable (though not surprising) aspects of high-altitude mountaineering is the semi-controversy over the use of supplemental oxygen, which many conider prudent but some old-school climbers seem to regard it as weak. (This mirrors a general attitude split in climbing circles about whether risk is something that should be minimized to the greatest extent possible or what makes climbing fun.) I'd be interested to see how attitudes towards viagra develop, especially if it becomes clearer that there's a specific physiological basis for nitric oxide treatment, rather than just a matter of some people being tougher than others.