Comparative hepatic transport of sulfobromophthalein and its glutathione conjugate in rats.

The hepatic transport of sulfobromophthalein (BSP) and its glutathione conjugate (BSP-GSH) were compared in rats by pharmacokinetic analysis in an attempt to determine the effect of conjugation on the over-all transfer of BSP from blood into bile. In the control rats, the plasma disappearance of BSP was faster than that of BSP-GSH, while the biliary excretion rate of BSP-GSH was significantly higher than that of BSP for the first 10 min. No significant difference in the total amount excreted in the bile for 4 hr was observed between two dyes. In the rats chronically intoxicated with carbon tetrachloride, typical delays were shown in both the plasma disappearance and the biliary excretion of BSP-GSH. In the control rats, the pharmacokinetic parameters, k12 and k23 of BSP-GSH were significantly smaller than those of BSP, while k34 was significantly greater than those of BSP. In the intoxicated rats, significant decreases were observed in k12, k23 and k34. The binding of BSP and BSP-GSH to the Y-fraction prepared from the control and intoxicated rats were studied by equilibrium dialysis. In the control rats, the number of high affinity bindings sites (n1) of BSP-GSH was significantly smaller than that of BSP, while no significant difference was revealed in the binding constant of the high affinity binding site (K1). In the intoxicated rats, both n1 and K1 of BSP-GSH were significantly smaller than those of the control rats. It was suggested that the glutathione conjugation might not play as the rate-determining step in the over-all hepatic transport of BSP.