HEPATIC-UPTAKE OF BROMOSULFOPHTHALEIN-GLUTATHIONE IN PERFUSED EISAI HYPERBILIRUBINEMIC MUTANT RAT-LIVER - A MULTIPLE-INDICATOR DILUTION STUDY

The hepatocellular uptake of the glutathione conjugate of bromosulfoph thalein (BSPGSH) was examined in Eisai hyperbilirubinemic rats (EHBR; originating from Sprague-Dawley rats), which lacked the ATP-dependent canalicular transport for non-bile acid organic anions, a trend common to Other mutant rat strains (TR- and GY, originating from Wistar rats ), Single-pass perfused rat liver experiments were conducted with BSPG SH (26-257 mu M) using the multiple indicator dilution technique, The steady-state extraction ratio of BSPGSH was close to zero due to lack of biliary excretion. After the introduction of a bolus dose containin g vascular (Cr-51-labeled red blood cells), interstitial (I-125-labele d albumin and [C-14]sucrose) and cellular space (D2O) indicators and [ H-3]BSPGSH into the portal vein, the outflow dilution profile of [H-3] BSPGSH was found to display a protracted declining profile (tailing) a t low input BSPGSH concentrations; the tail disappeared at higher BSPG SH concentrations, When data were fitted with the barrier-limited mode l of Goresky as used previously for BSPGSH for the Sprague-Dawley rat (SDR), model fitting was found to evoke an additional ''deep pool'' wi thin the hepatocyte to account for the ''tail'' component. The deep po ol became evident for the EHBR because biliary excretion of BSPGSH was absent and the rate of return from the deep pool was slow. The concen tration of BSPGSH within the deep pool was estimated to be 12 +/- 8 ti mes that in the cytosol, The binding of BSPGSH to EHBR S9 (effective b inding concentration of 53 mu M and a binding association constant K-A of 2.4 x 10(4) M-1), however, was found to be lower than that of SDR S9 and could not account for the late-in-time data. The influx permeab ility-surface area product was concentration dependent and decreased f rom 0.27 to 0.01 ml.sec(-1).g(-1) with increasing BSPGSH concentration ; the throughput component, or the portion of the dose that goes throu gh the liver without entering the hepatocyte, increased with increasin g concentration, The trends were characteristic of carrier-mediated tr ansport and were similar to those found for the uptake of BSPGSH in SD R.