THE FORMATION OF BILIRUBIN FROM HEMOGLOBIN IN VIVO*

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Abstract
After intravenous administration of Cl4-labeled hemoglobin or antibody-sensitized red cells to rats, biliary excretion of C14-bilirubin began within 30-50 minutes, was 50% completed in 3 hours, and ended within 22 hours. By contrast, injected C14-bilirubin was almost completely excreted within 1 hour, indicating that the delay between sequestration of heme pigment and excretion of C14-bilirubin was primarily due to the time required for conversion of heme to bilirubin in the reticuloendothelial system. Small doses of injected hemoglobin were almost completely converted to Cl4-bilirubin, but with large doses of hemoglobin or with sensitized red cells, only 58-80% of the ad-ministered heme was recovered as C14-bilirubin in the bile. It was suggested that the remaining heme was converted to excretory products other than bilirubin.