Metrizamide in experimental urography. V. Renal excretion mechanism of a non-ionic contrast medium in rabbit and cat

The excretion mechanisms of the non-ionic contrast medium, metrizamide, and the ionic, sodium diatrizoate, are compared to investigate the potential usefulness of metrizamide in clinical urography. A mixture of 125I-labeled metrizamide and 131I-labeled diatrizoate was injected intravenously to rabbits or cats. Urine, bile and blood were analyzed for their concentration of iodine. From these concentrations the renal and total clearance was calculated. In the rabbit the excretion of metrizamide was also compared with that of 3H-inulin with or without influence of p-aminohippurate or probenecid. The earlier reported relatively low urinary iodine concentrations after intravenous injection to rabbits of low doses were explained by the following findings: In the rabbit the volume of distribution, the renal clearance and the total clearance of metrizamide were smaller than those measured for diatrizoate and inulin. The biological half-life in serum measured 30-150 min after injection was the same for all three compounds. No indication of tubular secretion was found. The excretion mechanism of the contrast media exhibits species differences as no differences between metrizamide and diatrizoate in the parameters mentioned above could be measured in the cat.