NEOCYTOLYSIS - PHYSIOLOGICAL DOWN-REGULATOR OF RED-CELL MASS

It is usually considered that red-cell mass is controlled by erythropo ietin-driven bone marrow red-cell production, and no physiological mec hanisms can shorten survival of circulating red cells. In adapting to acute plethora in microgravity, astronauts' red-cell mass falls too ra pidly to be explained by diminished red-cell production. Ferrokinetics show no early decline in erythropoiesis, but red cells radiolabelled 12 days before launch survive normally. Selective destruction of the y oungest circulating red cells-a process we call neocytolysis-is the on ly plausible explanation. A fall in erythropoietin below a threshold i s likely to initiate neocytolysis, probably by influencing surface-adh esion molecules. Recognition of neocytolysis will require reexaminatio n of the pathophysiology and treatment of several blood disorders, inc luding the anaemia of renal disease.