The distribution, retention, and excretion of intravenously injected 241Am citrate have been investigated in a nonhuman primate. Seven adult female Kenya baboons which had been given 0.2 μCi/kg were studied for 817 days by a combination of techniques: (a) external counting of 60-keV γ of 241Am in vivo in both whole-body and partial-body geometries, (b) bioassay of liver and skull biopsy samples, and (c) radioanalysis of 241Am in excreta and baboon tissues at sacrifice. The data thus far confirm previously reported results (14, 17) that the major initial deposition sites of soluble 241Am in the baboon are the skeleton [35% of the injected dose (percentage ID) at 1 day] and liver (31% ID at 1 day). The elimination rate of 241Am from the liver was fairly rapid at 2.5%/day (T1/2 = 28 days), whereas the retention of 241Am in bone was long (at least several years). Americium-241 excreted during the first week after injection was detected principally in the urine, whereas the majority of Am excreted during the following 7 weeks was in feces, corresponding in the most part to elimination of Am from the liver. Microlocalization of Am in various soft tissues indicates general agreement with results previously reported for other species. However, americium in the baboon ovary at late times after injection is found as highly focalized sources, occurring principally in the outer cortical regions and associated with concretic structures. The implications of the findings of these studies with respect to metabolic parameters used for radiation dose calculations in man are discussed.

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