The role of the reticuloendothelial system in cerium 144 metabolism

Experiments were undertaken to shed light on the part played by the reticuloendothelial system (RES) in cerium-144 metabolism. Rats were given single intravenous injections with 10 μCi 144Ce in the form of CeCl2, carrier-free, and determinations made of resultant organ burdens and concentrations for liver and spleen, the major sites of RES activity, as well as other organs and tissues. Evidence was obtained that, in case trace amounts are administered, distribution of 144Ce in RES organs is non-uniform. It is pointed out that formation of complex compounds with liver protein fractions is of primary importance in 144Ce kinetics. In the author's view binding of the isotope to plasma protein fractions hinders the occurrence of hydrolyzation reactions. In such a colloid form, the radionuclide becomes more readily available for exchange and linkage with organic radicals in organs of deposition. From these experimental findings, there are grounds for a reevaluation of existing conceptions as to the part played by the RES in 144Ce metabolism; emphasis is namely placed on formation of complex compounds with cellular biosubstrates rather than hydrolyzation reactions in the fluid body compartment. (author)