Evaluation of effective renal plasma flow with I-127 ortho-iodohippurate and I-123 ortho-iodohippurate in rabbits

Rationale and Objectives. Radiolabeled ortho-iodohippurate is commonly empl oyed for evaluating effective renal plasma flow (ERPF) by means of either i n vivo scintigraphy and/or plasma clearance curves. A new method has recent ly been developed for measuring levels of stable iodine (iodine-127) in bio logic samples, based on the detection of x-ray fluorescence photons, In thi s study, the authors assessed the potential of the new system to evaluate E RPF by using an iodinated contrast medium with adequate glomerular filtrati on and tubular secretion properties. Materials and Methods. A commercial system was used to evaluate ERPF after intravenous injection of stable I-127 ortho-iodohippurate. The results were compared with the clearance values of I-123 ortho-iodohippurate, considere d the reference standard. Seven rabbits under general anesthesia were given intravenous injections of I-123 ortho-iodohippurate and I-127 ortho-iodohi ppurate. The corresponding plasma curves were evaluated from 4 to 60 minute s to calculate ERPF as the dose/integral of plasma curve. Results. The initial distribution volumes of I-123 ortho-iodohippurate (149 .4 mL/kg +/- 12.1) and I-127 ortho-iodohippurate (148.8 mL/kg +/- 11.8) wer e virtually superimposable, thus confirming the chemical identity of the tw o compounds. The plasma clearance values for I-127 ortho-iodohippurate (11. 15 mL/min kg(-1) +/- 1.44) were slightly (not significantly) higher than th ose fur I-123 ortho-iodohippurate (10.49 mL/min kg(-1) +/- 1.41), perhaps b ecause of a relative "mass" load effect of the iodinated medium. Conclusion. The results obtained in this study demonstrate the feasibility of the new system for evaluating ERPF, provided that a compound with adequa te glomerular filtration and tubular secretion properties is employed.