title: Elevation of the serum bilirubin diconjugate fraction provides an early marker for cholestasis in the rat.
abstract: OBJECTIVE
  During cholestasis, components normally excreted into bile, e.g. bilirubin, accumulate in liver cells and biliary passages. In order to assess the conjugation of bilirubin retained in the hepatocyte during cholestasis, we analyzed the pattern of bilirubin pigments in rat serum and bile, using reversed phase alkaline methanolysis-HPLC. Cholestasis was induced by bile flow interruption for 1 to 2 h.
  
  
  RESULTS
  One hour after initiation of cholestasis, the serum concentration of total bilirubin rose 2-fold due to increases in bilirubin di- (BDC) and monoconjugate (BMC), while unconjugated bilirubin (UCB) decreased by 33%. As a result, the BDC/BMC ratio increased to 1.67+/-0.20 vs 0.60+/-0.10 in controls (p<0.01) and the BMC/UCB ratio to 1.0+/-0.2 vs 0.1+/-0.1 (p<0.01). After relief of biliary obstruction, biliary output rose to 8.0+/-0.5 vs 5.5+/-0.3 micromol x min(-1) x kg (p<0.01), and the biliary BDC/BMC ratio to 4.0+/-0.3 vs 1.5+/-0.2 (p<0.01). In contrast, the biliary BMC/UCB ratio remained unchanged throughout. Increasing the duration of obstruction to 2 h led to a further increase in the serum BMC/UCB ratio to 2.2+/-0.3 (p<0.01), but not in the BDC/BMC ratio. Serum aminotransferase activity and the concentration of total bile acids increased 3- and 100-fold above their respective control values. Alkaline phosphatase activity remained unaltered, and electron microscopical features of cholestasis became apparent only after 2 h of biliary obstruction.
  
  
  CONCLUSIONS
  We suggest that one of the initial events of cholestasis is a more efficient conjugation of bilirubin retained in the hepatocyte. This results in a shift of the equilibrium among bilirubin pigments towards BDC, the end-product of conjugation. Such a shift provides an early marker for cholestasis.
authors.affiliation: Department of Medical Research, University of Leuven, Belgium.
authors.forename: V A
authors.initials: VA
authors.lastname: Mesa
authors.forename: R
authors.initials: R
authors.lastname: De Vos
authors.forename: J
authors.initials: J
authors.lastname: Fevery
mesh_terms: D000469:Alkaline Phosphatase / Q000097:blood; D000818:Animals; D001646:Bile / Q000737:chemistry; D001663:Bilirubin / Q000032:analysis / Q000097:blood*; D015415:Biomarkers / Q000097:blood*; D002779:Cholestasis / Q000097:blood*; D002851:Chromatography, High Pressure Liquid; D014453:Glucuronosyltransferase / Q000378:metabolism; D008099:Liver / Q000201:enzymology / Q000648:ultrastructure; D008297:Male; D008854:Microscopy, Electron; D051381:Rats; D017208:Rats, Wistar; D000637:Transaminases / Q000097:blood
chemical_list: D015415:Biomarkers; D014453:Glucuronosyltransferase; D000637:Transaminases; D000469:Alkaline Phosphatase; D001663:Bilirubin