Effects of prolonged irradiation by low dose-rate ionizing radiation on the hemopoiesis of mice

To evaluate the effects of prolonged exposure to ionizing radiation with low dose-rate on the hemopoiesis of mice, SPF C3H/HeN female mice were irradiated by 137Cs gamma-ray with doses of 0.1-0.5 Gy at the dose rate of 1 mGy/22hr/day. After irradiation, the numbers of hemopoietic cells contained in the bone marrow and spleen were determined by CFU-S and CFU-GM assays; the numbers of peripheral blood cells were counted. Precursor cells of day 12-CFU-S, which occurs in the earlier stage of hemopoietic cell differentiation, showed no remarkable changes as doses increased. No remarkable changes of the numbers of peripheral blood cells were observed. These results were much different from those at 20 mGy/22hr/day. Furthermore, long-term irradiation up to 8 Gy with 20 mGy/22hr/day depressed regeneration capacity of the hemopoietic microenvironment after injury. (author)