Detection of diffuse glomerular lesions in rats: II. Comparison of indium-111 cationic small macromolecules with technetium-99m DTPA.

Dextrans with average molecular weights of 5,000, 10,000, and 17,500 and inulin were rendered cationic by amination with 2-bromoethylamine hydrobromide. After limited coupling with DTPA cyclic dianhydride, they were labeled with 111In. A good correlation was found between their early renal uptake quantitated by camera-computer techniques and their renal clearance from multiple plasma samples in rats with glomerular damage induced by puromycin aminonucleoside and controls. However, there was poor correlation between the early renal uptake of these agents and the clearance of simultaneously injected [99mTc]DTPA. The 2-hr organ distribution and urinary excretion of these agents were compared with the corresponding values of DTPA. The differences in clearance between rats with glomerular damage and controls were greater with aminated dextran (mol wt 5,000) than with DTPA, confirming previous work with infusions of nonradioactive charged dextrans and neutral inulin. The cationic dextrans appear to reflect the presence or absence of the normal anionic charge of the glomerular membrane as well as changes in filtration rate. Aminated inulin did not differentiate between controls and rats with glomerular disease any better than DTPA, probably because the number of amino groups conjugated was insufficient to produce the charge effect.