Regulation of Haemopoietic Stem Cell Turnover in Partially Irradiated Mice

The existence of a possible local control of CFU turnover was studied in mice in which one tibia only was irradiated (LR mice) and in mice in which one tibia was shielded during whole‐body irradiation (‘TBR’mice). In both the LR and ‘TBR’mice, the increased CFU turnover continued in the irradiated tibiae even after the time when in the unirradiated (shielded) tibiae it returned to normal levels. The early temporary decrease in the CFU numbers in the shielded tibiae of ‘TBR’mice is attributed to a temporary demand for increased differentiation rather than to migration of CFU. The direct control of CFU turnover appears to be local in nature, in contrast to the stimulus for CFU differentiation.