Blaufox, M. Donald

Radioiodinated Hippuran was injected into the inferior vena cava of three unilaterally and three bilaterally nephrectomized dogs. Radioactivity was recorded over the precordium and remaining kidney in the former group and the precordium and renal fossa in the latter. The disappearance of I131 from plasma was analyzed and interpreted by two-compartment and three-compartment systems. Theoretical curves for cardiac and renal areas (constructed from analysis of arterial plasma samples) agreed well with curves from in vivo counting. Analyzed by either model, the first compartment exceeded the plasma volume severalfold, part seeming to be in the kidney. Extravascular compartments, impossible to sample, were not identified. About 15% of whole-blood radioactivity was in erythrocytes. Biliary excretion of Hippuran I131 was insignificant unless nephrectomy was bilateral; then up to 60% was excreted in the bile in 24 hr. Protein binding could not be demonstrated. Radiorenograms converted to fairly accurate rate constants may prove more useful than descriptive methods currently employed. Understanding the distribution and excretion of Hippuran appears helpful to accurate interpretation of the radiorenogram.

A study was made of the disappearance of sodium diatrizoate-I131 from the plasma of ten dogs after single intravenous injections. The plasma disappearance curves suggested a two-compartment system. The renal plasma clearance of diatrizoate-I131 calculated from these curves and the conventional renal plasma clearance of creatinine were not statistically different. Clearances calculated from the urinary excretion and midperiod plasma concentration of radioactivity in four experiments yielded values averaging 10% less than the creatinine clearance. Chromatographic studies of commercially available diatrizoate-I131 revealed the presence of about 5% free iodide and of about 5% of unidentified impurities. These impurities seem to account, partly at least, for the differences found between diatrizoate clearance and creatinine clearance. Biliary excretion and erythrocytic uptake of diatrizoate were minimal and did not appear to influence the analysis.