Erythropoiesis in the Rat under Continuous γ‐Irradiation at 45 rads/day

SUMMARY Radioactive iron has been used to study the response of erythropoiesis in rats during continuous γ‐irradiation at 45 rads/day. Haemoglobin and haematocrit values remain very nearly normal throughout the period of 19 weeks studied and there is only a small decrease in the red cell count at times later than 10 weeks. The lower than normal 59 Fe incorporation occurring during the first few weeks of irradiation appreciably underestimates red cell production. The marked fall in re‐populating ability indicates a considerable change in the mechanism by which red cell production is maintained after more than 6 weeks irradiation. The recovery of re‐populating ability following the termination of the irradiation after a period of 10 weeks suggests that 30 per cent of the re‐populating cells are killed each day by the continuous irradiation. The results presented do not show at which stage of erythropoiesis increased proliferation occurs. However, if all the increased proliferation should occur in the cells with re‐populating ability, an increase of 10–15 times would be required in their proliferation rate. An alternative method that has been proposed for measuring re‐populating ability employing irradiation with bone marrow shielding, instead of bone marrow transplantation is briefly discussed.