The toxicity of137 Cs in the beagle dog was investigated at the Inhalation Toxicology Research Institute (ITRI) and Argonne National Laboratory (ANL) as part of programs to evaluate the biological effects of both radionuclides in atomic bomb fallout and internally deposited fission-product radionuclides. In the ITRI study, young adult dogs were exposed once by intravenous injection to a range of137 Cs concentrations; the results have recently been published (Nikula et al., Radiat. Res. 142, 347-361, 1995). The purpose of the present report is to summarize the ANL study and to compare the results of the two studies. At ANL, 63 dogs in three age groups (15 juveniles, 142-151 days old; 38 young adults, 388-427 days old; and 10 middle-aged dogs, 1387-2060 days old) were given137 Cs intravenously at levels (61-162 MBq/kg) near those expected to be lethal within 30 days after injection. There were 17 control dogs from the same colony. Twenty-three of the dogs injected with137 Cs, including all middle-aged dogs, died within 52 days after injection due to hematopoietic cell damage resulting in severe pancytopenia that led to fatal hemorrhage and/or septicemia. The other significant early effect was damage to the germinal epithelium of the seminiferous tubules of all male dogs. These early effects are the same as those reported for the dogs injected with137 Cs at ITRI. In addition, the design of the ANL study revealed an age- and gender-related differential radiosensitivity for early effects: The middle-aged dogs died significantly earlier due to complications of hematological dyscrasia compared to the juvenile and young adult dogs, and the middle-aged females died significantly earlier than the middle-aged males. The most significant non-neoplastic late effects in the 137Cs-injected dogs from ANL and ITRI were atrophy of the germinal epithelium of seminiferous tubules with azoospermia, and a significant dose-dependent decrease in survival. However, the survival of the ANL dogs was decreased more than that of the ITRI dogs at similar radiation doses from 137Cs. Numerous neoplasms occurred at many different sites in the dogs injected with137Cs at ANL and ITRI. Two differences in the findings of the two studies were that (1) there was an increased risk for malignant thyroid neoplasms in the ANL male dogs injected with137Cs, but not the ITRI dogs of either gender, and (2) there was an increased relative risk for benign neoplasms excluding mammary neoplasms in the ITRI dogs injected with137 Cs, but not the ANL dogs. In both groups, there were dose-related increased incidences of malignant neoplasms, malignant neoplasms excluding mammary neoplasms, all sarcomas considered as a group, all non-mammary carcinomas considered as a group and malignant liver neoplasms. In summary, the similarity of the findings between the two studies and the dose-response relationships for survival and for large groupings of neoplasms suggests that these results are consistent findings in 137Cs-injected dogs and might be dose-related late effects in humans exposed to sufficient amounts of internally deposited137 Cs.

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