Stem cell (CFUs) proliferation inhibitor in blood of mice injected with hydroxyurea

Analysis of the mouse haemopoietic stem cell (CFUs) kinetics after hydroxyurea administration has provided an in vivo assay suitable for detection of factors which inhibit recruitment of non-proliferating G0-CFUs into cell cycle, or transit of CFU's through the G1 phase. Using this assay, it has been demonstrated that plasma obtained from mice which had received hydroxyurea approximately 12-14 hr previously, possesses a factor which inhibited the triggering of CFUs into the cell cycle. The appearance of this CFUs proliferation inhibitor occurred at a time when 60-70% of the CFUs were synchronized in the S phase of the cell cycle, as a consequence of hydroxyurea action. Some basic properties of the inhibitor were investigated.