Impaired activity of the bile canalicular organic anion... : Hepatology (original) (raw)

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Impaired activity of the bile canalicular organic anion transporter (Mrp2/cmoat) is not the main cause of ethinylestradiol-induced cholestasis in the rat

Koopen, Nynke R.1; Wolters, Henk1; Havinga, Rick1; Vonk, Roel J.1; Jansen, Peter L.2; Müller, Michael2; Kuipers, Folkert Ph.D.*, 1

1Groningen Institute for Drug Studies, Laboratory of Nutrition and Metabolism, University Hospital Groningen, Groningen, the Netherlands

2Groningen Institute for Drug Studies, Division of Gastroenterology and Hepatology, University Hospital Groningen, Groningen, the Netherlands

*Address reprint requests to: Groningen Institute for Drug Studies, Room Y2115 CMC IV, University Hospital Groningen, Hanzeplein 1, P.O. Box 30.001 9700RB Groningen, the Netherlands. Fax: 31-50-3611746.

Received July 21, 1997; Accepted October 16, 1997; previously published online December 30, 2003

Abstract

To test the hypothesis that impaired activity of the bile canalicular organic anion transporting system mrp2 (cmoat) is a key event in the etiology of 17α-ethinylestradiol (EE)-induced intrahepatic cholestasis in rats, EE (5 mg/kg subcutaneously daily) was administered to male normal Wistar (NW) and mrp2-deficient Groningen Yellow/Transport-deficient Wistar (GY/TR−) rats. Elevated plasma bilirubin levels in GY/TR− rats increased upon EE-treatment from 65 ± 8.4 μmol/L to 183 ± 22.7 μmol/L within 3 days, whereas bilirubin levels remained unaffected in NW rats. Biliary bilirubin secretion was 1.5-fold increased in NW rats but remained unaltered in GY/TR− rats. Plasma bile salt concentrations remained unchanged in both strains, although hepatic levels of the sinusoidal Na+-taurocholate cotransporting protein (ntcp) were markedly reduced. Biliary secretion of endogenous bile salt was not affected in either strain. A clear reduction of mrp2 levels in liver plasma membranes of NW rats was found after 3 days of treatment. The bile salt-independent fraction of bile flow (BSIF) was reduced from 2.6 to 2.0 μL/min/100 g body weight in NW rats with a concomitant 62% reduction of biliary glutathione secretion. The absence of mrp2 and biliary glutathione in GY/TR− rats did not prevent induction of EE-cholestasis; a similar absolute reduction of BSIF, i.e., from 1.1 to 0.6 μL/min/100 g body weight, was found in these animals. EE treatment caused a reduction of the maximal biliary secretory rate (SRM) of the mrp2 substrate, dibromosulphthalein (DBSP), from 1,040 to 695 nmol/min/100 g body weight (−38%) in NW rats and from 615 to 327 nmol/min/100 g body weight (−46%) in GY/TR− rats. These results demonstrate that inhibition of mrp2 activity and/or biliary glutathione secretion is not the main cause of EE-induced cholestasis in rats. The data indicate that alternative pathways exist for the biliary secretion of bilirubin and related organic anions that are also affected by EE.