The hepatic handling of 131I-labeled sulfobromophthalein in the dog. Comparison with sulfobromophthalein.

131I-labeled BSP is obtained by the incorporation of one molecule of radioactive iodine in BSP. The purpose of this work was to study the influence of the added iodine on the hepatic extraction and biliary excretion of BSP. Two types of experiments were performed. In the first, a compartmental analysis of BSP and 131I-labeled BSP disappearance curves was performed after the simultaneous injection of 5 mg per kg of b. wt. of BSP and 10 muCi of 131I-labeled BSP: both, the plasma to liver and liver to bile transfer rates were significantly lower for 131I-labeled BSP than for BSP; the liver to plasma transfer rates were not significantly different. In the second series of experiments, the hepatic uptake of BSP and 131I-labeled BSP was estimated by the multiple indicator dilution technique: the extraction of BSP (59% +/- SD 5) was significantly higher than that of 131I-labeled BSP (35% +/- SD 5) (P less than 0.001). In conclusion the labeling of BSP with 131I significantly modified the hepatic handling of the dye; 131I-labeled BSP cannot therefore be used as a tracer of BSP.