Acquired Radioresistance: A Review of the Literature and Report of a Confirmatory Experiment

The ability of experimental animals to develop significant radioresistance by prior exposure to small doses of x radiation seems to be well established. An experiment is reported which shows that for control adult female white Swiss mice, Walter Reed strain, the LD/sub 50(30)/ is 487 plus or minus 25.7 r. If they are given 50 r WBR 10 days prior, it increases to 560 r plus or minus 31.0 r; and if the interval is 17 days, it is 617 r plus or minus 32.0 r. In this experiment radioresistance was manifest at both 10 and 17 days after the small exposure. Analysis of spleen and thymus weights under the conditions of these experiments gave no clue io the mechanism of the acquired radioresistance. Alternate hypotheses have been suggested, but the phenomenon remains unexplained. (auth)