Abstract

Gallium-68 (Tj, 68 minutes) can be used as a scanning agent for the detection of bone lesions when sufficient carrier gallium is administered. The data obtained in this study support the hypothesis that the high blood levels of gallium that are observed at early time periods (hours) when small quantities of gallium are administered i.v. are due to its binding by serum constituents. Gallium binding by rabbit serum was demonstrated through ultrafiltration, gel filtration and equilibrium dialysis. Studies with ultrafiltration suggest that the binding component has a molecular weight greater than 10,000. Studies with gel filtration indicate that the binding component belongs to the class of 280-mµ absorbing materials with a molecular weight greater than 5000. Equilibrium dialysis experiments also suggest that a high molecular weight component in the serum is responsible for the binding of gallium. The percentage of added gallium (citrate form) bound by rabbit serum decreases at concentrations above 3.6 x 10-3 µmol/10 ml of serum and drops to 4% at a concentration of 7.2 µmol/10 ml. Increasing the concentration of citrate causes a drop in gallium binding by the serum but only at relatively high concentrations of citrate. Binding was relatively insensitive to pH change when the pH was greater than 6.5.