Bile pigment excretion: a comparison of the biliary excretion of bilirubin and bilirubin derivatives.

Abstract

The mechanism of excretion of 4 tetrapyrroles (bilirubin, mesobilirubin, mesobilirubinogen, and optically inactive (i) urobilin) was studied in normal and Gunn rats. 3H-labeled tetrapyrroles were prepared, and their radiochemical purity was established. On intravenous administration, each was rapidly excreted in bile by normal rats, but only mesobilirubinogen and i-urobilin were excreted in substantial quantities by Gunn rats. In the normal species studied, 90% of the bilirubin and mesobilirubin excreted was in the form of the glucuronide conjugate. In contrast, a major fraction of excreted mesobilirubinogen and i-urobilin appeared in the bile intact and unaltered. Glucuronide conjugation of bile pigments may be governed by a specific molecular configuration: unsaturation of the outer (a,c) tetrapyrrole bridges.