TECHNETIUM-99M-L,L-ETHYLENEDICYSTEINE - A RENAL IMAGING AGENT .1. LABELING AND EVALUATION IN ANIMALS

L,L-ethylenedicysteine (L,L-EC) can be labeled efficiently with Tc-99m at pH 12 to obtain a highly pure and very stable tracer agent (Tc-99m-L,L-EC). The biological behavior of Tc-99m-L,L-EC was studied in mice and a baboon. In mice, Tc-99m-L,L-EC demonstrated a more rapid urinary excretion and less retention in the kidneys, the liver, the intestines, and the blood than did Tc-99m-MAG3 at 10 and 60 min p.i. Urinary excretion decreased in probenecid pretreated mice, which indicates active tubular transport. In the baboon, the renograms for Tc-99m-MAG3 and Tc-99m-L,L-EC were comparable. Plasma-protein binding of Tc-99m-L,L-EC was lower than that of Tc-99m-MAG3 while its distribution volume and 1-hr plasma clearance were clearly higher. The promising results of the animal experiments suggest that Tc-99m-L,L-ethylenedicysteine may be a useful alternative to Tc-99m-MAG3 for renal function studies in humans.