OBJECTIVE:To investigate the pathway through which Calculus Bovis Sativus (CBS) up-regulates hepatic multidrug resistance-associated protein 2 (Mrp2) and Mrp4 in 17α-ethynylestradiol (EE)-induced cholestasis.METHODS:Five groups of rats were designed:control group,EE+ICI182780 group,EE group,EE+CB5 50 mg/kg group and EE + CBS 150 mg/kg group.CBS (50 and 150 mg.kg-1· d-1) was orally given to rats by gavage for five consecutive days in coadministration with EE.The levels of cholestasis biomarkers,alanine aminotransferase (ALT),aspartate aminotransferase (AST),alkaline phosphatase (ALP) and total bilirubin (TBIL) were determined by biochemical methods.The bile flow was measured.The histopathology of the liver tissue was evaluated.The expression of Mrp2,Mrp3,Mrp4,estrogen receptor α (ERα) and ERβ was determined by West blotting.RESULTS:CBS markedly improved EE-induced cholestasis.EE exposure significantly reduced hepatic Mrp2 and Mrp4 expression compared with the control group.EE also dramatically up-regulated the expression of Mrp3.Compared to the EE group,CBS notably up-regulated hepatic Mrp2 and Mrp4 but failed to influence the Mrp3 level significantly.ICI182780,an ER antagonist,showed similar beneficial effects as CBS.Decreased expression of Mrp2 and Mrp4 caused by EE was also restored by IC1182780.Additionally,EE significantly induced hepatic ERα expression,which was reversed by ICI182780 or CBS (150 mg/kg) treatment,suggesting that CB5 exerted a moderate regulatory effect on ER signaling.CONCLUSION:CBS up-regulated hepatic Mrp2 and Mrp4 expression in EE-induced cholestasis,which might be associated with its regulation of ER signaling.