Solution properties of sulfobromophthalein sodium (BSP) compounds alone and in association with sodium taurocholate (TC)

A series of in vitro studies have been performed utilizing the techniques of ultracentrifugation, freezing point depression, vapor pressure osmometry, and spectrophotometry, to study the colloid-chemical characteristics of various sulfobromophthalein sodium (BSP) compounds in aqueous solution and to evaluate the possibility of a direct physicochemical interaction between BSP and taurocholate (TC). The results of these studies indicate that: (1) BSP compounds self-associate in aqueous solution to form polymolecular aggregates. These aggregates are larger with unconjugated BSP, where the aggregation number appears to increase with the concentration of BSP, compared with the more polar glutathione conjugate of BSP. (2) There is a marked physicochemical interaction between unconjugated BSP and TC and a much smaller effect between the bile salt and conjugated BSP. This interaction was minor between BSP and glycodeoxycholate or taurodehydrocholate but was reproduced fully by glycocholate. Such an interaction between BSP and TC may have physiologic importance and may help to explain the previously noted facilitated excretion of BSP observed after infusion of TC in experimental animals.