The effectiveness of repeated bronchopulmonary lavage for removing inhaled l4We fused clay particles from the lungs of Beagle dogs was investigated. Twelve Beagle dogs were exposed to a 144Ce fused clay aerosol resulting in initial lung burdens ranging from 47-64 pCi/kg body weight. Eight received 10 saline lavage treatments, five on each lung over a 56-day period. At the end of each lavage, they also received 50 mg of calcium diethylenetriaminepentaacetic acid (DTPA) intravenously. Four dogs received no treatment. A second group of four dogs was exposed to an aeorsol of fused clay only and given 10 lung lavages over a 56-day period. I n the eight treated dogs, an average of 44% of initial lung burden was removed by the 10 lavage procedures. Recovery from two of these eight dogs was considerably lower, 23 and 27%, than the average of the remaining 6, 51%. The reason for this has not been established. Examination of the urinary excretion showed that although the DTPA injections increased urinary excretion 10 fold, this difference between the treated and untreated dogs accounted for only 1.6% of the initial lung burden. Thus, for 144Ce inhaled in this form, the lavage procedure was 28 times more effective in removing '44Ce from the body than were the DTPA injections. The reduction in initial lung burden over a 56-day treatment period resulted in a decrease of the cumulative radiation dose to the lung, at 90 days and infinity, to 53 and 57%, respectively, of that found for the untreated dogs. No significant clinical changes due to treatment were observed in these animals. All of the dogs in this study were alive at 90 days post-exposure and are now under observation in the colony.

To evaluate the lifetime hazards of exposure to ionizing radiation, 1,680 beagles received whole-body exposures to 60Co gamma rays or sham exposures during development. Eight groups of 120 dogs each received mean doses of 16-18 or 81-88 cGy at 8, 28 or 55 days of gestation, or at 2 days after birth. One group of 120 dogs received a mean of 83 cGy at 70 days of age and one group of 240 dogs received a mean of 81 cGy at 365 days of age. Sham irradiations were given to 360 controls. Sexes were equally represented. In 1,343 dogs allowed to live out their life span, heritable lymphocytic thyroiditis with hypothyroidism was a major contributor to mortality. Irradiated dogs had a decreased risk for hypothyroidism, a finding that was surprising and not easily explained. Of the 1,343 life-span dogs, those exposed as neonates at 2 days of age or as juveniles at 70 days of age had evidence for an increased risk for thyroid follicular cell neoplasia. Hypothyroid dogs had a significantly increased risk for thyroid neoplasia, including greater risk for carcinomas, but no evidence of a greater sensitivity to radiation-induced tumors. In dogs with normal thyroid function irradiated at 2 or 70 days of age there was increased risk for benign and malignant follicular cell neoplasms, including multiple neoplasms. No difference between sexes was noted. These findings related to age sensitivity in the dog were consistent with the high risk for radiogenic thyroid neoplasia in humans after exposure during early childhood.

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