57Co-EDTA renal imaging in rats

We studied the synthesis of Co-57-EDTA (E gamma = 122 keV), its biodistribution in Wistar rats and its blood and urinary elimination compared with that of Cr-51-EDTA. We added 6 mu mol EDTA diluted in 3-5 mi isotonic phosphate buffer (Na2HPO4) to a commercial (CoCl2)-Co-57 radioactive tracer solution. The incubation period was 15 min. Quality control was performed using TLC and HPLC. Six healthy Wistar rats underwent Co-57- EDTA renography for 30 min. In one rat, additional TLC and HPLC was performed on blood tone sample only) and urine samples (n = 3) obtained 30 min, 30 min, 2 h and 4 h following injection of 18.5 MBq Co-57- EDTA and Cr-51-EDTA respectively. Radioisotope quantification was done by means of a germanium detector. Co-57 was chelated to EDTA at high yield (K-stab = 10(E)36). No free or protein-bound Co-57 was found. The ratio of Cr-51-EDTA to Co-57-EDTA remained constant (P = 0.133, n = 4). Co-57-EDTA was rapidly cleared from the blood pool (heart), and prompt and high target-to-background ratios for both kidneys were obtained (mean=8.4, range=7-12). At the end of the acquisition, activity remaining in the body excluding kidney and bladder was 45+/-5.2%. No specific activity uptake was noted in any other organ or tissue. We conclude that Co-57-EDTA is a promising radioligand for simultaneous clearance and separate renal function estimation. Its preparation is straightforward and, in rats, no free or protein-bound Co-57 was found. (C) 2000 Lippincott Williams & Wilkins).