Effects of strontium-90 plus external irradiation in C57BL/6J mice.

421 C57BL/6J female mice were subdivided into 11 groups. Five of these groups were given 300 rad total body irradiation from a 137Cs source at an age of 65 days. One day later, these irradiated mice were treated intraperitoneally with varying amounts of 90Sr (0, 0.032, 0.10, 0.32, and 1.0 mu Ci/g of body weight). Five groups of mice that had not been irradiated were treated on the same day with the same doses of 90Sr as given the five irradiated groups, and a sixth unirradiated group was treated with 2 mu Ci/g body weight. Each mouse treated with 90Sr and still alive was monitored between 249 and 303 days later in a total body well scintillation detector; mice with counts that differed by more than approximately 50% from the mean for their group were eliminated. A total of 402 mice were accepted for the experiment; these mice were followed to the end of their life span and then autopsied. Mice treated with the highest doses of 90Sr (1.0 and 2.0 mu Ci/g) experienced significantly elevated number of deaths from infections relative to the control group; these deaths occurred relatively early after 90Sr injection, and were particularly severe in the group of mice that had received 300 rad of external irradiation in addition to 1.0 mu Ci90Sr/g. There was no evidence of synergism between 90Sr injection and 300 rad external irradiation for production of bone tumors. Tumors of the type that occur spontaneously in C57BL/6J mice appeared to be more frequent in 90Sr-treated mice and in externally irradiated mice than in controls, but the numbers of excess tumors in these groups were not statistically significant (P less than 0.09).