Radium Retention in Mature Beagles Injected at 5 Years of Age

Retention of 226 Ra was substantially lower in mature beagles injected at 5 years of age compared to corresponding values for young adult beagles injected at 17 months of age. As with young adults, the percentage retention in mature dogs given about 10 μCi/kg exceeded that in mature dogs given 4 μCi/kg or less. Percentage retention, R, at t days after the injection of 10 μCi/kg in mature beagles could be represented by the equation, $R=64.1e^{-0.233t}+13.0e^{-0.00481t}+22.9e^{-0.000329t}$, and for mature beagles given 4 μCi/kg or less, $R=38.8e^{-0.40t}+30.6e^{-0.0424t}+11.9e^{-0.00567t}+18.7e^{-0.000352t}$. Measured ^{222}{\rm Rn}/{}^{226}{\rm Ra}$ ratios in bone were similar in mature and young adults. Roughly 66% of the injected radium was excreted by mature dogs during the first 3 weeks, about two-thirds of the total excretion appearing in the feces. Distribution of 226 Ra within the skeleton was similar in mature and young adult beagles.