Role of rat multidrug resistance protein 2 in plasma and biliary disposition of dibromosulfophthalein after microsomal enzyme induction.

We have previously demonstrated that microsomal enzyme inducers phenobarbital (PB) and pregnenolone-16alpha-carbonitrile (PCN), but not 3-methylcholanthrene (3-MC) and benzo(a)pyrene (BaP), increase expression and function of rat Multidrug Resistance Protein 2 (Mrp2), a canalicular organic anion transporter. Thus, the purpose of this study was to determine whether Mrp2 protein induction alters the biliary and plasma dispositions of dibromosulfophthalein (DBSP). After four daily ip injections of PB, PCN, 3-MC, BaP, or vehicle, DBSP (100 mg/kg) was injected iv and was measured in blood and bile over a 40-min period. PB and PCN significantly enhanced plasma disappearance and biliary excretion of DBSP, whereas 3-MC and BaP did not. To determine whether the enhanced plasma disappearance and biliary excretion was entirely due an increase in Mrp2, PCN was also administered ip daily for 4 days to Mrp2-null Eisai hyperbilirubinemic (EHBR) rats and then injected iv with DBSP. PCN significantly increased plasma DBSP disappearance in EHBR rats during early time intervals (2-20 min), but not at later time intervals (25-40 min). PCN did not increase DBSP biliary excretion in EHBR rats, but actually decreased it at later time intervals. In summary, the increase in Mrp2 protein after microsomal enzyme induction is responsible for increased biliary DBSP excretion. Furthermore, the increase in Mrp2 protein after microsomal enzyme induction is not responsible for the enhanced plasma DBSP disappearance at early time points, yet may influence plasma DBSP disappearance at later time points. This study also demonstrates the importance of compensatory hepatic transporters in eliminating DBSP by alternative pathways other than Mrp2.