Submit a comment

Bilirubin Diglucuronide Formation in Intact Rats and in Isolated Gunn Rat Liver
J. Roy Chowdhury, … , Allan W. Wolkoff, Irwin M. Arias
J. Roy Chowdhury, … , Allan W. Wolkoff, Irwin M. Arias
Published March 1, 1982
Citation Information: J Clin Invest. 1982;69(3):595-603. https://doi.org/10.1172/JCI110486.
View: Text | PDF
Research Article

Bilirubin Diglucuronide Formation in Intact Rats and in Isolated Gunn Rat Liver

Abstract

Bilirubin diglucuronide (BDG) may be formed in vitro by microsomal UDP glucuronosyl transferase (EC 2.4.1.17)-mediated transfer of a second mole of glucuronic acid from UDP-glucuronic acid, or by dismutation of bilirubin monoglucuronide (BMG) to BDG and unconjugated bilirubin, catalyzed by an enzyme (EC 2.4.1.95) that is concentrated in plasma membrane-enriched fractions of rat liver. To evaluate the role of these two enzymatic mechanisms in vivo, [3H]bilirubin mono-[14C]glucuronide was biosynthesized, purified by thin-layer chromatography, and tracer doses were infused intravenously in homozygous Gunn (UDP glucuronyl transferase-deficient) rats or Wistar rats. Bilirubin conjugates in bile were separated by high-pressure liquid chromatography and 3H and 14C were quantitated. In Gunn rats, the 14C:3H ratio in BDG excreted in bile was twice the ratio in injected BMG. In Wistar rats the 14C:3H ratio in biliary BDG was 1.25 ± 0.06 (mean ± SEM) times the ratio in injected BMG. When double labeled BMG was injected in Wistar rats after injection of excess unlabeled unconjugated bilirubin (1.7 μmol), the 14C:3H ratio in BDG excreted in bile was identical to the ratio in injected BMG. Analysis of isomeric composition of bilirubin conjugates after alkaline hydrolysis or alkaline methanolysis indicated that the bile pigments retained the IXα configuration during these experiments. The results indicate that both enzymatic dismutation and UDP glucuronyl transferase function in vivo in BDG formation, and that dismutation is inhibited by a high intrahepatic concentration of unconjugated bilirubin. This hypothesis was supported by infusion of [3H]bilirubin-monoglucuronide in isolated perfused homozygous Gunn rat liver after depletion of intrahepatic bilirubin by perfusion with bovine serum albumin (2.5%), and after bilirubin repletion following perfusion with 0.34 mM bilirubin. From 20 to 25% of injected radioactivity was recovered in BDG in bile in the bilirubin-depleted state; only 8-10% of radioactivity was in BDG in bile after bilirubin repletion.

Authors

J. Roy Chowdhury, N. Roy Chowdhury, Ulrich Gärtner, Allan W. Wolkoff, Irwin M. Arias

×

Guidelines

The Editorial Board will only consider comments that are deemed relevant and of interest to readers. The Journal will not post data that have not been subjected to peer review; or a comment that is essentially a reiteration of another comment.

  • Comments appear on the Journal’s website and are linked from the original article’s web page.
  • Authors are notified by email if their comments are posted.
  • The Journal reserves the right to edit comments for length and clarity.
  • No appeals will be considered.
  • Comments are not indexed in PubMed.

Specific requirements

  • Maximum length, 400 words
  • Entered as plain text or HTML
  • Author’s name and email address, to be posted with the comment
  • Declaration of all potential conflicts of interest (even if these are not ultimately posted); see the Journal’s conflict-of-interest policy
  • Comments may not include figures
This field is required
This field is required
This field is required
This field is required
This field is required
This field is required