The Interaction of Yttrium with Physiological Ligands

Abstract

The deposition of radioactive yttrium in bone has generated considerable interest for a number of reasons. Not only is yytrium a fission product of some importance, but its chemistry and behavior in the animal differ markedly from that of calcium. Yttrium tends to deposit selectively in resorption cavities (1, 2). Calcium tends to concentrate in areas of new growth (3). Both, however, seem to be interacting with the inorganic crystals (4, 5). To account for these peculiar differences, several groups of investigators have sought answers in terms of the physicochemical state of yttrium in body fluids and its mode of transport in vivo (4, 6, 7). Experimentally, however, many difficulties are encountered because of yttrium's tendency to hydrolyze in near-neutral solutions. Dearnaley (8), for example, avoided the problem of hydrolysis (and simultaneously sharply delimited the physiological significance of the results) by studying the complexing of yttrium by various ligands at acid pH only (5.3 or less). Despite the difficulties involved, the present studies were undertaken to survey various physiologically important ligands for their ability to interact with yttrium at physiological pH. Admittedly, the results must be regarded as semiquantitative at best and qualitative at worst. The number of interacting variables (carrieryttrium concentration, age of colloid, size of colloid, nature of reaction vessel, etc.) is so great that it is virtually impossible to apply sophisticated methodology at the present time. Accordingly, relatively simple parameters were investigated with relatively simple techniques, such as filtration, ultrafiltration, and electrophoresis. Although final conclusions are not possible at the present time, the results are very compatible with earlier studies of beryllium transport (9): that is, (1) at