210Pb Studies in Beagles

Abstract

Carrier-free 210Pb was administered intravenously to 10 young adult beagles in a sodium citrate citric acid solution (pH 3.5). Retention was determined by total-body counting of the 47-keV gamma-ray. Total excreta collections from three dogs for the first three weeks after injection were assayed intact for their 210Pb content by gamma-ray counting. About 75% of the excreted 210Pb appeared in the feces. The fraction of the injected activity still in the circulating blood was 40% at 1 day, 14% at 1 week and 3% at 1 month. By 1 hr following injection, red cells contained more than 99% of the 210Pb that was in blood. During the first 1600 days after administration the biological retention of injected Pb could be described by the equation, R = 69.7 e−0.0555t + 16.9 e−0.00376t + 13.4 e−0.000140t, where R = per cent retention at t days after injection. One dog sacrificed 28 days after administration had about 63% of the retained 210Pb in the skeleton, 20% in the liver, 8% in the blood and 9% in other soft tissues. Assuming a skeletal mass equal to 7.5% of body weight at injection, the skeleton had the highest concentration of any tissue measured. Liver concentration was about 0.8 times that of the skeleton. Relative liver concentration was much lower in two dogs sacrificed 1100 and 1497 days after injection, 0.03 and 0.005 times that in the skeleton, which contained 97 and 99%, respectively, of the 210Pb retained in the total-body at death. The effectiveness of injected 210Pb for osteosarcoma production in beagles appeared to be not greatly different from that of 226Ra. At long times after injection, the 210Po/210Pb ratio in the skeleton was close to 1.0.