Flow Cytometric Analysis of Micronucleus Induction in Mouse Erythrocytes by γ-irradiation at Very Low Dose-rates

Abstract

Male CBA-S mice were subjected to protracted γ-irradiation. Two groups of five animals were each exposed to dose rates of 6 and 30 mGy/day for 56 days, respectively, upon which irradiation was terminated and the groups were followed for an additional 49 days. Frequencies of micronucleated poly-and normochromatic erythrocytes in peripheral blood samples were determined before (day 0), during (day 14, 28 and 56), and after (day 70 and 105) irradiation using flow cytometry. A second experiment was performed as above, but with exposure limited to 7 days. Frequencies of micronucleated polychromatic erythrocytes in bone marrow and peripheral blood were determined. Significantly elevated frequencies of micronuclei in peripheral blood polychromatic erythrocytes were found for the 30-mGy/day dose group on day 14, 28 and 56 and for the 6-mGy/day dose group on day 28 and 56. In normochromatic erythrocytes from peripheral blood significantly elevated frequencies were found on all sampling occasions with mouse given 30 mGy/day, while those given 6 mGy/day showed significantly elevated frequencies on day 28, 56 and 70. The frequencies of micronucleated polychromatic erythrocytes were found to be similar in bone marrow and peripheral blood, while the frequencies of micronucleated normochromatic erythrocytes were consistently lower than for micronucleated polychromatic erythrocytes at all samplings for all groups. On day 28 the frequencies (mean ± SE) of micronucleated polychromatic erythrocytes in peripheral blood were 0·0016 ± 0·0001 for the control group, 0·0019 ± 0·0001 for the 6-mGy/day group and 0·0028 ± 0·0003 for the 30-mGy/day group. The results show an elevated induction of micronuclei in erythroblasts at a dose rate of approximately 3 mGy per cell cycle.