CONICET | Buscador de Institutos y Recursos Humanos

In previous studies we observed that repeated administration of the cholestatic estrogen EE to rats (5 mg/Kg, 5 consecutive days) reduces the expression of the canalicular transporter multidrug resistance-associated protein 2 (Mrp2), whereas basolateral Mrp3 is increased. Mrp3 induction is linked to Mrp2 downregulation, accumulation of Mrp common substrates into the hepatocyte (induction by substrate) being postulated as a potential mechanism. Aim: To evaluate if induction of Mrp3 protein by EE may result alternatively from direct modulation of Mrp3 gene by EE. Methodology: Adult male Wistar rats (n=3) received a single dose of EE (5 mg/kg, s.c.) or its vehicle (propyleneglycol, controls (C)). Six h later, bile flow and biliary excretion of bile salts and glutathione were determined and liver samples collected. In separated experiments, hepatocytes isolated from normal rats were cultured for 4 h in the presence of EE (1 or 10 mM, or propyleneglycol). Total RNA was extracted from liver samples and from cultured hepatocytes. Mrp3 mRNA was determined by quantitative RT-PCR. Results: bile flow (C=1.43±0.22 vs EE=1.23±0.12 ml/min/g liver) and biliary excretion rate of bile salts (C=51±10 vs EE=48±4 mmol/min/g liver) and glutathione (C=2.43±0.63 vs EE=1.30±0.35 mmol/min/g liver) were not affected by the single dose of EE, indicating absence of cholestasis. Mrp3 mRNA significantly increased in EE rat liver (300%, p<0.05) as well as in cultured hepatocytes exposed to 10 mM EE (400%, p<0.05). Conclusion: in vivo Mrp3 mRNA induction occurred in spite of absence of cholestatic symptoms (which rules out accumulation of Mrp substrates). Induction of mRNA also occurred in cultured hepatocytes, shortly after incorporation of EE. Taken together, these results suggest a direct modulation of Mrp3 gene by EE.