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Keywords:

  • bile flow;
  • bile formation;
  • bile salt synthesis;
  • cholangiocyte;
  • cholate kinetics;
  • cholehepatic shunt

Abstract

Background/Aims: Bile flow consists of bile salt-dependent bile flow (BSDF), generated by canalicular secretion of bile salts, and bile salt-independent flow (BSIF), probably of combined canalicular and ductular origin. Bile salt transport proteins have been identified in cholangiocytes, suggesting a role in control of BSDF and/or in control of bile salt synthesis through cholehepatic shunting.

Methods: We studied effects of bile duct proliferation under non-cholestatic conditions in multidrug resistance-2 P-glycoprotein (Abcb4)-deficient multidrug resistance gene-2 (Mdr2(−/−)) mice. BSDF and BSIF were determined in wild-type and Mdr2(−/−) mice during infusion of step-wise increasing dosages of tauroursodeoxycholate (TUDC). Cholate synthesis rate was determined by 2H4-cholate dilution. Results were related to expression of transport proteins in liver and intestine.

Results: During TUDC infusion, BSDF was increased by ∼50% and BSIF by ∼100% in Mdr2(−/−) mice compared with controls. Cholate synthesis rate was unaffected in Mdr2(−/−) mice. Hepatic expression of the apical sodium-dependent bile salt transporter (Asbt), its truncated form (tAsbt) and the multidrug resistance-related protein 3 were upregulated in Mdr2(−/−) mice.

Conclusions: Bile duct proliferation in Mdr2(−/−) mice enhances cholehepatic shunting of bile salts, which is associated with a disproportionally high bile flow but does not affect bile salt synthesis.