Neocytolysis in the adaptation of red cell mass on descent from altitude.

Abstract

Acclimated individuals descending from high altitude must rapidly adapt to plethora, an excess in red cell mass and blood volume for their new environment. We believe that this is accomplished by neocytolysis, the selective destruction of the youngest red blood cells, physiologic process we recently discovered through studies on astronauts. On entering microgravity, an astronaut's blood distributes centrally causing acute plethora. There ensues a reproducible 10% decline in red ceil mass in the first several days in space. Red cell production does not decline in these first days, and survival of labeled older red cells is normal. The inescapable. conclusion is that neocytolysis ensues. Studies done 45 years ago in Peru and in the Himalayas clearly demonstrate hemolysis on descent from high altitude. There is a 10% decline in red cell mass in the first several days at sea level, an increase in serum bilirubin and stool urobilin, all occurring before there is any significant fall in red cell production. We preview studies on acclimated subjects descending from high altitude which will directly demonstrate neocytolysis by selectively labeling red cell cohorts of different ages. These studies will elucidate underlying mechanisms of neocytolysis, whether sub-threshold erythropoietin levels affect surface adhesion molecule expression and red cell-phagocyte interactions. Neocytolysis may have broad implications to clinical medicine, including to current dosing regimens of erythropoietin.