Ito, Kousei, Tomokazu Koresawa, Koichi Nakano, and Toshiharu Horie. Mrp2 is involved in benzylpenicillin-induced choleresis. Am J Physiol Gastrointest Liver Physiol 287: G42-G49, 2004; 10.1152/ajpgi.00416.2003 180 mol/kg), a classic ␤-lactam antibiotic, was intravenously given to Sprague-Dawley (SD) rats and multidrug resistance-associated protein 2 (Mrp2)-deficient Eisai hyperbilirubinemic rats (EHBR). A percentage of the [ 3 H]PCG was excreted into the bile of the rats within 60 min (SD rats:

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... 31.7% and EHBR: 4.3%). Remarkably, a transient increase in the bile flow (ϳ2-fold) and a slight increase in the total biliary bilirubin excretion were observed in SD rats but not in the EHBR after PCG administration. This suggests that the biliary excretion of PCG and its choleretic effect are Mrp2-dependent. Positive correlations were observed between the biliary excretion rate of PCG and bile flow (r 2 ϭ 0.768) and more remarkably between the biliary excretion rate of GSH and bile flow (r 2 ϭ 0.968). No ATP-dependent uptake of [ 3 H]PCG was observed in Mrp2-expressing Sf9 membrane vesicles, whereas other forms of Mrp2-substrate transport were stimulated in the presence of PCG. GSH efflux mediated by human MRP2 expressed in Madin-Darby canine kidney II cells was enhanced in the presence of PCG in a concentration-dependent manner. In conclusion, the choleretic effect of PCG is caused by the stimulation of biliary GSH efflux as well as the concentrative biliary excretion of PCG itself, both of which were Mrp2 dependent. bile flow; multidrug resistance-associated protein; ␤-lactam