Metabolism of injected barium in six healthy men

Data are presented on the early metabolism and long-term retention of 133Ba (half-life 10.74 y) injected into six healthy male volunteers at ages 25-81 y. The tracer appeared to be mainly skeletal within several days, much earlier than predicted by the ICRP's model of alkaline earth metabolism. Excretion was mainly fecal, the relative fecal:urinary clearance up to 14 d ranging from 6 to 15 in the six subjects. The whole-body retention at 50 d (mean 8%, range 4.5 to 12%) was similar to that inferred from published data on the retention of injected Ra in man (mean 7%, range 3-13%). For about 1 y thereafter, the retention of Ba could be represented by simple power functions of time, with the rate of loss correlating with the excretory plasma clearance rate inferred over the first 4 d. In the subject aged 81 y, the pattern differed from that established following an earlier injection at age 60, but the differences were not necessarily related to advancing age.