title: Negative feedback regulation of the ileal bile acid transport system in rodents.
abstract: BACKGROUND
  Active transport of conjugated bile acids by ileal enterocytes is a key mechanism for conservation of the bile acid pool. Experiments were performed to determine whether such transport is regulated by substrate load.
  
  
  METHODS
  Using anesthetized biliary fistula guinea pigs or rats, the ileum was perfused with ursodeoxycholyltaurine at a concentration causing maximal ileal transport of this bile acid; absorption was assessed by biliary recovery. Before ileal perfusion, animals ingested one of three diets: chow, chow with added conjugated bile acid, or chow with added cholestyramine.
  
  
  RESULTS
  In the guinea pig, ingestion of a taurocholate-enriched diet resulted in a 75% decrease in the absorption rate of ursodeoxycholyltaurine. Similar results were obtained with cholylsarcosine (a deconjugation-dehydroxylation resistant analogue) or with chenodeoxycholylglycine, the endogenous bile acid of the guinea pig. In contrast, cholestyramine ingestion caused an increase in ursodeoxycholyltaurine absorption. In the rat, cholyltaurine or cholylsarcosine ingestion also caused decreased ileal transport. In the guinea pig, maximal down-regulation of active ileal bile acid transport occurred after 2-3 days of bile acid feeding; up-regulation required 3-4 days.
  
  
  CONCLUSIONS
  Bile acid metabolism is regulated by feedback inhibition of active ileal transport in addition to the well-established feedback inhibition of bile acid biosynthesis in the liver. Together, these two regulatory mechanisms ensure constancy of bile acid secretion.
authors.affiliation: Department of Physiological Chemistry, University of Lund, Sweden.
authors.forename: J
authors.initials: J
authors.lastname: Lillienau
authors.forename: D L
authors.initials: DL
authors.lastname: Crombie
authors.forename: J
authors.initials: J
authors.lastname: Munoz
authors.forename: S J
authors.initials: SJ
authors.lastname: Longmire-Cook
authors.forename: L R
authors.initials: LR
authors.lastname: Hagey
authors.forename: A F
authors.initials: AF
authors.lastname: Hofmann
mesh_terms: D000818:Animals; D001647:Bile Acids and Salts / Q000008:administration & dosage / Q000737:chemistry / Q000378:metabolism*; D001693:Biological Transport, Active / Q000187:drug effects; D004032:Diet; D005246:Feedback; D006168:Guinea Pigs; D007082:Ileum / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013656:Taurocholic Acid / Q000494:pharmacology; D013997:Time Factors
chemical_list: D001647:Bile Acids and Salts; D013656:Taurocholic Acid