Biological effects of 137CsCl injected in beagle dogs.

The toxicity of intravenously administered 137CsCl in the beagle dog was investigated as part of a program to evaluate the biological effects of internally deposited fission-product radionuclides. The intravenous route of exposure was chosen for simplicity and accuracy because it was known that after intravenous injection, inhalation or ingestion, internally deposited 137CsCl is rapidly absorbed and distributed throughout the body, exposing the whole body to beta-particle and gamma radiations. Fifty-four dogs were injected intravenously with 137Cs to provide one group of six dogs with mean initial body burdens of 141 MBq 137Cs/kg body mass and four groups of 12 dogs each with mean initial body burdens of 104, 72, 52 and 36 MBq 137Cs/kg. Twelve dogs were injected with isotonic saline as study controls. Because the number of study control dogs was small, data from an additional 49 control dogs from other studies at the Inhalation Toxicology Research Institute that were performed over a similar span of years were also used. There was a significant, dose-dependent decrease in survival of the 137Cs-injected dogs. Eleven 137Cs-injected dogs, including all six in the highest initial body burden group, died within 81 days after injection, primarily due to hematopoietic cell damage resulting in severe pancytopenia. An additional 25 dogs had transient hematological dyscrasia but survived for long times. All 137Cs-injected male dogs had marked damage to the germinal epithelium of the testicular seminiferous tubules with azoospermia in the long-term survivors. Benign and malignant neoplasms occurred in a variety of organs in 137Cs-injected dogs, rather than in a single target organ. When individual organs were considered, the incidence of malignant neoplasms was increased in the liver and in the nasal cavity and paranasal sinuses of the 137Cs-injected dogs. There was a 137Cs treatment effect in the incidence of malignant neoplasms (P < 0.001) in male dogs but no 137Cs-related treatment effect in female dogs. However, when malignant mammary neoplasms were excluded from the analysis, there was no gender difference, and there was a dose-related response (P < 0.001) in both males and females for the incidence of malignant neoplasms.