STUDIES OF THE DIPYRRYLMETHENE (“FUSCIN”) PIGMENTS. III. THE VARIABLE FATE OF BILIRUBIN DEPENDING UPON CONJUGATION AND OTHER FACTORS*

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Abstract
Comparison of the recovery of urobilinogen, bilirubin, and mesobilifuscin in the feces of human subjects who had been fed by tube with solutions of crystalline N15 bilirubin as the sodium salt indicates that mesobilifuscin is not a significant conversion product of bilirubin. Measurement of mesobilifuscin did not reconcile discrepancies between hemoglobin destruction and urobilinogen excretion, nor did it account for the failure to demonstrate conversion of tube-fed bilirubin to urobilinogen. In contrast to free bilirubin, tube-fed conjugated bilirubin from human bile was much more readily accounted for by the amount of fecal urobilinogen. Crystalline bilirubin given intravenously in 0.1 M Na2CO3 solution was apparently conjugated in the liver and was largely recovered as fecal urobilinogen. A case of refractory anemia is described in which an abnormal pathway of bilirubin metabolism was demonstrated. In this instance, in contrast to the normal control observations, tube-fed bilirubin glucuronide or intravenously administered crystalline bilirubin was largely unaccounted for as urobilinogen, mesobilifuscin, or bilirubin, in the excreta. In the same individual no evidence could be obtained of faulty conjugation of bilirubin or hydrolysis of the conjugate in the small intestine, nor was there any failure to account for tube-fed mesobilirubinogen (i-urobilinogen). The possibility is considered that there was abnormal reabsorption of bilirubin.