A direct assessment of the importance of conjugation for biliary transport of sulfobromophthalein sodium.

Abstract

Abstract The importance of conjugation for maximal excretion of sulfobromophthalein sodium (BSP) into bile has been examined directly by comparison of the biliary excretion of dye when either free or conjugated BSP was administered intravenously to mature rats and guinea pigs. Conjugated BSP was prepared by: (1) harvesting the major conjugate (BSP-glutathione) from paper chromatograms of bile collected from rats receiving a constant infusion of free BSP, and (2) synthesis in vitro and isolation in relatively pure form by a new method described in the text. Maximal dye excretion into bile was approximately doubled when conjugated rather than free dye was given to both rats and guinea pigs, despite a slower initial rate of uptake of the conjugated dye by the liver of both species. The results are interpreted as indicating that conjugation of BSP facilitates dye transport into bile, and, moreover, in vivo is the rate-limiting step in the over-all transport of injected free BSP from blood to bile. The possible mechanisms by which conjugation facilitates transport are discussed.