BIOLOGICAL EFFECTS OF (CSCL)-CS-137 INJECTED IN BEAGLE DOGS OF DIFFERENT AGES

The toxicity of Cs-137 in the beagle dog was investigated at the Inhal ation Toxicology Research Institute (ITRI) and Argonne National Labora tory (ANL) as part of programs to evaluate the biological effects of b oth radionuclides in atomic bomb fallout and internally deposited fiss ion-product radionuclides. In the ITRI study, young adult dogs were ex posed once by intravenous injection to a range of Cs-137 concentration s; the results have recently been published (Nikula et al., Radiat. Re s. 142, 347-361, 1995). The purpose of the present report is to summar ize the ANL study and to compare the results of the two studies. At AN L, 63 dogs in three age groups (15 juveniles, 142-151 days old; 38 you ng adults, 388-427 days old; and 10 middle-aged dogs, 1387-2060 days o ld) were given Cs-137 intravenously at levels (61-162 MBq/kg) near tho se expected to be lethal within 30 days after injection. There were 17 control dogs from the same colony. Twenty-three of the dogs injected with Cs-137, including all middle-aged dogs, died within 52 days after injection due to hematopoietic cell damage resulting in severe pancyt openia that led to fatal hemorrhage and/or septicemia. The other signi ficant early effect was damage to the germinal epithelium of the semin iferous tubules of all male dogs. These early effects are the same as those reported for the dogs injected with Cs-137 at ITRI. In addition, the design of the ANL study revealed an age- and gender-related diffe rential 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 fem ales died significantly earlier than the middle-aged males. The most s ignificant non-neoplastic late effects in the Cs-137-injected dogs fro m ANL and ITRI were atrophy of the germinal epithelium of seminiferous tubules with azoospermia, and a significant dose-dependent decrease i n survival. However, the survival of the ANL dogs was decreased more t han that of the ITRI dogs at similar radiation doses from Cs-137. Nume rous neoplasms occurred at many different sites in the dogs injected w ith Cs-137 at ANL and ITRI. Two differences in the findings of the two studies were that (1) there was an increased risk for malignant thyro id neoplasms in the ANL male dogs injected with Cs-137, but not the IT RI dogs of either gender, and (2) there was an increased relative risk for benign neoplasms excluding mammary neoplasms in the ITRI dogs inj ected with Cs-137, but not the ANL dogs. In both groups, there were do se-related increased incidences of malignant neoplasms, malignant neop lasms 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 fin dings in Cs-137-injected dogs and might be dose-related late effects i n humans exposed to sufficient amounts of internally deposited Cs-137. (C) 1996 by Radiation Research Society