Strain differences in carcinogenic and hematopoietic responses of mice after injection of plutonium citrate

The carcinogenicity of injected (239)Pu citrate was compared in female mice of the C3H, C57BL/6 and BC3F(1) hybrid strains with different spectra of spontaneous or radiation-induced tumors. A significant reduction in survival due to early death caused particularly by the induction of osteosarcomas was noted in each strain after injection of 500 Bq or more. The dose response of osteosarcomas appeared to have a similar pattern in each strain except for the differences in the skeletal dose ranges for the maximum induction. While the incidence of lymphoid tumors decreased as that of osteosarcomas increased sharply to the maximum at higher doses, their histological phenotypes were predominantly non-thymic, pre-B-cell leukemic lymphomas compared to the controls in each strain. Myeloid leukemias were not highly induced in any of the control and (239)Pu-injected mice, and solid tumors involving the other organs were reduced in each strain after injection of 500 Bq or more. To follow up the hematological kinetics related to alpha-particle irradiation of bone marrow stem cells, sequential examinations were done in mice of each strain within 1 year after injection of 5000 Bq. The numbers of peripheral white blood cells and bone marrow cells were consistently reduced in each strain from 90 days on, while spleen cells increased from 180 days on. Granulocyte-macrophage and macrophage colony-forming cells were also consistently reduced in the bone marrow, with a compensatory increase in the spleen from 90 days on. These findings indicate that the carcinogenic and hematopoietic responses were specific to alpha-particle irradiation and were independent of mouse strain after injection with (239)Pu citrate.