Two types of acquired radioresistance after low doses of X-rays in mice

Recovery from radiation injury has been extensively studied such as in split-dose irradiations. But the overshooting recovery in survival rate after multiple exposures in irradiated animals was scarcely observed. Maisin et al. first reported that pre-irradiation of rats, with as low as 5 cGy of X-rays, increased 30-day survival rate when the animals were again exposed to a sub-lethal dose about 10 weeks later. Though the increment was not statistically significant, the study suggested there may be some stimulation after low dose exposure to ionizing radiation. In a previous paper authors confirmed that acquired radioresistance was induced in (male) mice 2 months after exposure to 5-10 cGy of X-rays, and that recovery of endogenous CFUs was stimulated by the pre-irradiation. This study examines when the radioresistance appears after exposure to 5 cGy of X-rays, and how long it lasts. Result is compared with the acquired radioresistance induced with the priming dose of more than 20 cGy. (author). 5 refs., 4 tabs