Dose response at low doses of X-irradiation and MMS on the induction of micronuclei in mouse erythroblasts

Abstract

The test of induced micronuclei in erythrocytes of mammalian bone marrow constitutes, because of its high experimental resolution power, a suitable method for the screening of induced chromosomal lesions at very low dosages of chemicals or irradiations. This test was used for a comparative investigation of the effect of low dose levels of X-irradiation and of the alkylating agent methyl methanesulphonate (MMS). The dose-effect curve of X-irradiation indicated a deviation from linearity at 10 rad, showing a significantly stronger effect than expected on extrapolation from the control to 100 rad. This deviation from linarity, however, only appeared at a low dose rate (18 R/min), whereas a linear dose-effect relation was indicated with a high dose rate (95 R/min). Experiments at 10 rad with different dose rates at two different current potentials suggested that this effect of the dose rate is more pronounced with soft than with hard X-irradiation. The induction of micronuclei with MMS follows a drastically different dose-effect curve as compared with X-irradiation. The relative efficiency of the treatment is lowest at low concentrations, presumably as a result of the efficient repair process at such dose levels. Simultaneous treatment with X-rays and MMS at low dose levels only resulted in an additive effect. This suggests that X-irradiation does not interfere with the repair process operating with MMS. The difference in the dose-effect relations of X-irradiation as compared with MMS may be brought back to the fact that X-rays, in contrast with MMS, produce double-strand breaks.