The Retention and Distribution of 241 Am and 65 Zn, Given as DTPA Chelates in Rats and of [ 14 C]DTPA in Rats and Beagles

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Abstract
Retention and distribution of 241Am and 65Zn, given as the DTPA (diethylenetriaminepentaacetic acid) chelates, were studied in rats for 48 h following i.v. injection. The retention and distribution of [14C]DTPA, injected as the Zn chelate, was determined in rats and 2 beagles. At 24 h postinjection (PI) rats retained 5% of the 241Am, 35% of the 65Zn and 4% of the [14C]DTPA. The loss of these nuclides from blood plasma was described by the sum of 2 exponentials and in rats the respective biological half-lives (t1/2) for early times PI were t1/2 65Zn = 1.4 h, t1/2 241Am = 0.75 h and t1/2 [14C]DTPA = 0.65 h; the 2nd component t1/2 for 241Am, 65Zn and [14C]DTPA were 0.2, 6 and 1.6 days, respectively. In beagles the initial t1/2 for loss of [14C]DTPA from blood was 0.77 h and the 2nd component t1/2 was 4.4 days. The urine was the primary route of excretion in both species. In both rats and dogs, the kidney and liver contained the highest concentration of 241Am, 65Zn and [14C]DTPA. The concentration of 65Zn in the liver reached a plateau after .apprx. 4 h. Significant amounts of 65Zn, however, were found in the lung, spleen and femur. In rats the tissue: plasma concentration ratios of [14C]DTPA in most organs studied peaked at about 4 h PI. In dogs the concentration of [14C]DTPA in all soft tissues, except for the brain, exceeded that of plasma at 52 h PI. In the skeleton the concentration was less than in plasma.