Effect of Stable Scandium on the Long-term Whole Body Retention of Intravenously Administered 46Sc Citrate in the Rat

Abstract

The effect of stable scandium on the whole-body retention and tissue distribution of 46Sc (T1/2 = 84 days) has been studied in the rat. In one group of animals high specific activity 46Sc was administered intravenously; in another group 46Sc with added stable scandium (0.5 mg/kg) was administered. The retention was followed for 333 days at which time the animals were killed and the distributions of the 46Sc in various tissues determined. In general, administration of stable scandium produced pronounced increases in tissue concentrations, particularly in liver, marrow, intestine, and brain. A least-squares analysis indicated that three exponential components were required to fit the whole-body retention data from both. groups of animals. For “carrier-free” 46Sc the three compartments observed were: (1) 21% with a biological half time of 1.0 day (turnover rate constant, lambda = 0.69 day−1); (2) 22% with a biological half time of 7.1 days (lambda = 0.098 day−1); and (3) 56% with a biological half time of 485 days (lambda = 0.0014 day−1). For 46Sc with stable scandium, the three compartments observed were: (1) 23% with a biological half-time of 1.3 days (lambda = 0.53 day 1); (2) 16% with a biological half time of 7.3 days (lambda = 0.095 day−1); and (3) 62% with a biological half time of 1200 days (lambda = 0.00058 day−1). Stable scandium thus has a pronounced effect an the long-term whole-body retention of 46Sc. The observed long-term biological half-times in rats for both 46Sc and 46Sc plus carrier were far in excess of that given in IRCP Publication 2, 1959, for 46Sc (30 days).