Abstract

The plasma binding and conjugation kinetics of bromosulfophthalein (BSP) with glutathione (GSH) were studied in the single-pass in situ perfused rat liver (portal vein perfusion at 10 ml/min); GSH in postmitochondrial fractions of the liver at the end of the experiment was examined as a potential rate-determining factor. BSP was highly bound to 1% albumin with at least two classes of binding sites: one of 0.17 site with an association constant of 1.9 x 10(7) M-1, and one of 7.4 equivalent sites of association constant, 1.3 x 10(5) M-1. Nonlinear binding was observed within between 5-1500 microM BSP. At varying input concentrations (0.4-250 microM) of BSP, the unbound fraction was extremely low (< 0.005) and the hepatic extraction ratio declined from 0.67 to 0.15; loss of BSP was primarily caused by GSH conjugation to form BSP-GSH, which appeared exclusively in bile. Additionally, unchanged BSP and two very minor unidentified metabolites were also excreted in bile. The formation of BSP-GSH proceeded with an apparent Vmax of 22 nmol/min/g and a KM of 0.05 microM, whereas the parameters for BSP excretion were 0.85 nmol/min/g and 0.02 microM, respectively. Within the concentration range of BSP examined, GSH availability did not appear to be rate-limiting in the formation or excretion of BSP-GSH.(ABSTRACT TRUNCATED AT 250 WORDS)