Persistent dose-dependent increases in cycling of haemopoietic precursor cells after irradiation.

Between 3 weeks and 36 months after irradiation of mice, there was a dose-dependent increased level of cycling in haemopoietic stem cells (CFU-S) and in granulocyte-macrophage precursor cells (GM-CFC). For CFU-S the percentage kill measured using the thymidine suicide technique increased from about 10% in controls to a high and persistent average level of about 45% after 10 Gy gamma-rays, and for GM-CFC the increase was from about 30% to about 50%.