The enterohepatic circulation of bile acids in mammals: form and functions
Alan F. Hofmann
Division of Gastroenterology. Department of Medicine, University of California, San Diego. La Jolla, California 92093-0063
TABLE OF CONTENTS
- 1. Abstract
- 2. Introduction
- 3. Bile acids: chemistry and metabolism
- 3.1. Overview
- 3.2. Bile acid conjugation
- 4. Components of the enterohepatic circulation
- 4.1. Overview
- 4.2. Structure of primary bile acids
- 4.3. Input of secondary bile acids
- 4.4. Hepatobiliary loop
- 4.4.1. Bile acid uptake by the hepatocyte
- 4.4.2. Bile acid biotransformation in the hepatocyte
- 4.4.3. Bile acid transport through the hepatocyte
- 4.4.4. Canalicular secretion of bile acids and bile acid induced bile flow
- 4.4.5. Bile acid biosynthesis
- 4.4.6. Postcanalicular event: cholangiocyte modification of bile
- 4.4.7. Cholehepatic shunting of bile acids
- 4.5. The Enteral loop
- 4.5.1. Ileal transport of bile acids
- 4.5.2. Colonic absorption of bile acids
- 4.6. The Extrahepatic (systemic) Loop
- 5. Modeling the enterohepatic circulation of bile acids
- 6. Regulation of the enterohepatic circulation
- 6.1. Regulation of input of primary bile acids
- 6.2. Regulation of intestinal conservation
- 7. Methods for quantifying the enterohepatic circulation
- 7.1. Measurement of bile acid synthesis (and loss)
- 8. Enterohepatic cycling of drugs
- 9. Functions of the enterohepatic circulation of bile acids
- 9.1. Hepatobiliary functions
- 9.2. Intestinal functions
- 9.3. Hormonal functions
- 10. Epilogue
- 11. Acknowledgements
- 12. References
1. ABSTRACT
The features of the enterohepatic circulation of bile acids in mammals are reviewed. Inputs into the circulating bile acids are primary bile acids synthesized from cholesterol in the hepatocyte and secondary bile acids formed by bacterial modification of primary bile acids in the distal intestine. Intestinal conservation of bile acids generates pools of individual bile acids whose relative sizes determine biliary bile acid composition. Efficient hepatic clearance results in low plasma bile acid levels, and virtually no renal excretion. Methods for characterizing the enterohepatic circulation are summarized. Bile acids have numerous physiological functions in the liver, biliary tract, and intestine resulting from their signaling and physicochemical properties.
