PRE-EXPOSURE OF MICE TO LOW DOSE OR LOW DOSE RATE IONIZING RADIATION REDUCES CHROMOSOME ABERRATIONS INDUCED BY SUBSEQUENT EXPOSURE TO HIGH DOSE OF RADIATION OR MITOMYCIN C

The phenomenon of cytogenetic adaptive and cross-adaptive response induced by low dose irradiation and chemical mutagen in mice is described. We found, firstly, that adapration can be induced by acute low dose X-irracliation (0—100 mGy). Secondly, a cross-adaptation can occur between X-irradiatlon and rrdto-mycin C (MMC). And finally, mice pre-exposed to chronic low dose rate ^60Co-Gamma irradiation (0-226. 0 mGy/day) are less susceptible to chromosome aberration induced by subsequent acute higher X-irradiation. Therefore, our data suggest that radioadaptlve respotrse depends on dose, dose rate and time interval. Possible mechanisms are also discussed.