Effects of a Continuous Irradiation with Low Dose-Rate Ionizing Radiation on the Hemopoiesis of Mice

Abstract

Since studies on the hemopoietic system have been recognized to be radio-sensitive, the mechanisms underlying cell proliferation and differentiationare well investigated.
We show here the effects of a continuous irradiation with low dose-rate ionizing radiation on the hemopoiesis of mice. SPF(specific pathogen free) female C3H/HeN mice were irradiated with various doses of 1-8 Gy ¹³⁷Cs γ-rays at the dose rate of 20 mGy/22h/day. After irradiation, the number of hemopoietic cells in the bone marrow was determined by the methods of CFU-S and CFU-GM assay, and the number of peripheral blood cells was also counted. It was shown that the day 12-CFU-S decreased as the dose increased. Decrease of 7days-CFU-S colonise and CFU-GM colonies. All of these colony-forming cells were reduced to about 50 % of the unirradiated controls at the dose of 8 Gy. Regardless of a decrease in the number of hemopoietic stem cells, no remarkable changes were observed in the number of peripheral blood cells, indicating the possibility of an enhanced differentiation of the precursor cells.