Effect of BrdUrd and low doses of gamma radiation on sister chromatid exchange, chromosome breaks, and mitotic delay in mouse bone marrow cells in vivo.

We have measured, in mouse bone marrow cells in vivo, the ability of low doses of gamma radiation to induce sister chromatid exchanges (SCEs) in unifilarly 5-bromodeoxyuridine (BrdUrd)-substituted DNA. Also examined was the effect of BrdUrd incorporation on SCE induction by radiation, the comparative frequency of SCE and chromosome breaks induced by gamma radiation, the ability of ionizing radiation to interfere with normal cellular proliferation, and the relationship between proliferative inhibition and SCE and chromosome break frequency. A direct relationship between the number of SCEs and gamma radiation dose was observed, an effect which was dependent on BrdUrd incorporation. The frequency of SCE was 80 times higher than that of chromosome aberrations in cells with BrdUrd-substituted DNA, and there was no difference between the frequency of SCE in cells with or without chromosome breaks. The mitotic delay increased with the time between irradiation and harvesting. There was no relationship between the extent of mitotic delay and the number of SCEs.