Kinetics of erythroid and myeloid stem cells in post-hypoxia polycythaemia

The number of erythroid burst-(BFU-E) and colony-forming units (CFU-E), as well as of myeloid-macrophage colony-forming units (CFU-C), has been evaluated in tibial marrow and spleen of ex-hypoxic polycythaemic mice, at sequential time intervals after the end of hypoxia. In both marrow and spleen, the kinetics of the CFU-E pool is characterized by a sharp fall from above normal to lower than normal values. BFU-E and CFU-C however rise from below normal to higher than normal levels. These results have been correlated with both the erythropoietin (Ep) and the erythropoietic activity curves. It is apparent that Ep levels largely control both the differentiation and the amplification of the CFU-E pool and it is suggested that Ep may act as a 'survival factor' at the CFU-E level and/or increase the flow of cells from BFU-E to CFU-E. The difference in response between CFU-E and BFU-E favours a clearcut distinction between these populations, whereas the similarity between the BFU-E and CFU-C response suggest a close relationship between these two cell populations. It is also of interest that the murine spleen functions as a large reservoir of erythroid microenvironment for hypoxia-induced stress erythropoiesis.