SULFOBROMOPHTHALEIN SODIUM (BSP) CONJUGATION AND EXCRETION IN FETAL GUINEA PIGS.

Unconjugated and conjugated S 35 -labeled BSP were administered to viable fetal guinea pigs with intact placental circulation. Guinea pig placenta was virtually impermeable to unconjugated and conjugated BSP, thus permitting a comparison of the disposition of both dye compounds in the fetus, and additional comparison with adult guinea pigs receiving comparable weight-adjusted doses of BSP. Although conjugated BSP disappeared more slowly from plasma than unconjugated BSP in fetal and adult animals, it was delivered more rapidly into bile, indicating a shorter hepatic phase for conjugated BSP. The rate of delivery of both dye compounds into bile was considerably decreased in fetal guinea pigs when compared with values in adult animals. Biliary excretion of administered unconjugated BSP was disproportionately depressed, however, indicating that conjugation of BSP was impaired. Excretion of conjugated BSP into bile was also impaired in the fetus. Since conjugation appears to be impaired to a greater extent than excretion of conjugated and unconjugated BSP into bile in near-term fetal guinea pigs, conjugation, rather than excretion, is rate limiting in BSP delivery into bile in these animals.