title: Localization of glutathione conjugation activities toward bromosulfophthalein in perfused rat liver. Studies with the multiple indicator dilution technique.
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)
authors.affiliation: Faculty of Pharmacy, University of Toronto, Ontario, Canada.
authors.forename: Y
authors.initials: Y
authors.lastname: Zhao
authors.forename: C A
authors.initials: CA
authors.lastname: Snel
authors.forename: G J
authors.initials: GJ
authors.lastname: Mulder
authors.forename: K S
authors.initials: KS
authors.lastname: Pang
mesh_terms: D000818:Animals; D001798:Blood Proteins / Q000378:metabolism; D004912:Erythrocytes / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism*; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D007201:Indicator Dilution Techniques; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D008102:Liver Circulation / Q000502:physiology; D008297:Male; D010477:Perfusion; D011168:Portal System / Q000502:physiology; D011485:Protein Binding; D051381:Rats; D017207:Rats, Sprague-Dawley; D013448:Sulfobromophthalein / Q000378:metabolism* / Q000493:pharmacokinetics
chemical_list: D001798:Blood Proteins; D013448:Sulfobromophthalein; D005982:Glutathione Transferase; D005978:Glutathione