The Early Appearing Bilirubin: Evidence for Two Components *

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Abstract
The early appearing or shunt bilirubin is studied in human subjects given intravenous glycine 2-C14 and C14 labelled delta-aminolevulinic acid ([DELTA] ALA 4-C14). Following the glycine 2-C14 the labelling pattern of plasma bilirubin exhibited two peaks, the first at 12 to 24 hours and a second at 3 to 5 days. When [DELTA] ALA 4-C14 Was the precursor, one peak of bilirubin activity was found in the plasma at 1.5 to 6 hours. There was no second peak and labelling of red cell heme was minimal. It is suggested that the early labelled bile pigment consists of two components, the first being independent of red cell heme synthesis and having its origin primarily in the liver. The second component is dependent on red cell heme synthesis and arises primarily in the bone marrow. The labelling pattern in pernicious anemia suggests that both components are increased, while that in cases previously designated as shunt hyperbilirubinemia indicates the marrow to be the main site of bilirubin production.