Brief Report: Bilirubin Formation in the Liver from Nonhemoglobin Sources : Experiments with Isolated, Perfused Rat Liver

Rapid formation of C¹⁴-bilirubin from glycine-2-C¹⁴ or δ-aminolevulinic acid-4-C¹⁴ has been demonstrated in isolated, perfused rat liver. The kinetics of labeled bilirubin production in vitro were similar to those of the "early labeling" pigment fraction observed in intact rats. The magnitude of bile pigment formation from C¹⁴-ALA by isolated liver was comparable to that in intact animals. Derivation of the C¹⁴-bilirubin from hepatic degradation of labeled hemoglobin was excluded by perfusion of the liver with blood poor in reticulocytes, or with plasma. The findings identify the liver as an important source of the "early-labeling" pigment fraction.