Regeneration of erythroid committed precursor cells in polycythaemic mice treated with cyclophosphamide.

The recovery of erythroid stem cells and pluripotent haemopoietic stem cells (CFUS) was estimated in mice treated with cyclophosphamide (Cy) by measuring CFUS, the erythroid repopulating ability (ERA) of bone marrow cells and erythropoietin responsive cells (ERC). The experiments were performed in hypertransfused CBA mice previously injected with 200 mg/kg Cy. CFUS, ERA and response to a single dose of erythropoietin-Ep (5 U) were measured at 24 h time intervals for 7, 4 and 8 days respectively. The proliferation rate of CFUS and erythroid repopulating cells was estimated on the basis of cytosine arabinoside (AraC) suicide data. The results obtained demonstrate that CFUS and ERA do not regenerate at the same rate. ERA recovery preceded CFUS regeneration at the time when the Ep response was depressed. The proliferation rate of CFUS decreased with regeneration of CFUS while AraC suicide of erythroid repopulating cells remained high at the time when ERA had recovered to 80% of control values.