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

131I-labeled BSP is obtained by the incorporation of one molecule of radioactive iodine in BSP. The influence of the added iodine on the hepatic extraction and biliary excretion of BSP was studied. 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 5mg per kg of BSP and 10μCi of 131I-labeled BSP: both, the plasma to liver and liver to bile transfer rates were significantly lower for 131I-labelled 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 that than of 131I-labeled BSP (35%+-SD5) (P<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