Erythroid stem cell regeneration in normal and plethoric mice treated by cytosinarabinoside

Cytosinarabinoside (6 x 40 mg/kg in 4 h intervals) was used to study hemopoietic regeneration in normal and in hypertransfused mice. About 70-80% of pluripotent stem cells (CFUs), more than 80% of granuloid committed precursors (CFUc) and more than 95% of erythroid committed precursors (CFUE) were eliminated after treatment, and also more than 99% of the erythroblasts in the bone marrow smears. There was no regular difference between normal and hypertransfused groups. Regeneration started at day 2, with control levels of CFUs at day 3 and then overshooting, control levels of CFUc at days 4-5 and a single increase of CFUE at day 3. This rise in CFUE, with values well above control levels, was also present in hypertransfused mice, although less pronounced. In hypertransfused mice the CFUE peak was not allowed by an increase in erythroblast numbers in the femora or 6 h 59Fe uptake into femora or spleen-in contrast to non-plethoric controls. The results indicate the partial Ep independence of regenerating CFUE, as found after treatment with hydroxyurea.