Which of the following are considered lower abundance locations for ASBT?

• A. Other portions of small and large intestine
• B. Cholangiocytes in the liver
• C. Epithelium of proximal renal tubules
• D. All of the above

Answer: (D)

ASBT is the transporter that drives active reabsorption of bile acids in the ileum, but its expression isn’t limited to that one spot. In other parts of the gastrointestinal tract, ASBT is present at lower levels, so these segments can reabsorb some bile acids, just not as efficiently as the ileum. In the liver, cholangiocytes lining the bile ducts also show low-level ASBT expression, allowing a small amount of bile acid reuptake from bile within the biliary system. In the kidney, the proximal tubule epithelium expresses ASBT at a low level too, contributing to reclamation of filtered bile acids and reducing urinary loss. Putting that together, all of these tissues exhibit lower abundance of ASBT compared with the ileum, which is why all of the above locations are considered lower abundance sites.