Distribution and excretion of lanthanides: comparison between europium salts and complexes

Europium (^152,154Eu) was intravenously injected into rats as: (i) the chloride salt at pH 7.4, (ii) the chloride salt at pH 3, (iii) the albumin complex and (iv) the DTPA complex, and tissue uptake was determined 24 h later. For the chlorides, the target organ for uptake was liver (about 60% of dose) whilst europium complexes were rapidly excreted in urine and were predominantly taken up into the kidney (about 0.5% of dose) and bone. Liver uptake of EuCl₃, pH 7.4, corresponded to that of a colloidal material with most ¹⁵²Eu present in the non-hepatocyte population; however, EuCl₃, pH 3, was handled in a different manner, with significant uptake by hepatocytes. The differing tissue distributions of EuCl₃ and Eu-albumin suggest that plasma albumin does not readily bind injected EuCl₃. Renal uptake of europium, although a relatively low proportion of the injected dose, was associated with many subcellular fractions, including lysosomes, suggesting significant intracellular uptake and thus possible retention.