226 DEVELOPMENT OF BILIRUBIN CONJUGATION IN HUMAN NEW-BORNS

Abstract

The gestational age at which conjugation of bilirubin (BR) begins is unknown, and the BR conjugates initially formed have not been identified. Using alkaline methanolysis-HPLC and TLC, chemical, and enzymic tests on ethyl anthranilate azoderivatives, we determined and characterized the BR fractions in duodenal bile (DB) from 8 fullterm jaundiced infants (age 4-9 days) and in plasma from (1) cord blood (C) obtained at 46 unselected deliveries and from (2) 54 premature (P) and fullterm (F) newborns. In DB, BRs (50-317 μM) consisted of 1-12% unconjugated BR, 32-50% mono- and 43-67% di-ester conjugates ; the conjugating sugars corresponded with xylosyl (up to 5%), glucosyl (3-12%), and glucuronyl (83-96%) groups. Total plasma BR (TB) in C averaged 20±7.9 μM and consisted entirely of unconjugated BR. In P and F, TB increased from 29 to 116 μM during the 1st week, peaking at 5 days. In contrast with C, BRs in P and F comprised 2-5% BR glucuronides ; monoconjugates appeared during the 1st day, and diconjugates were detectable only 48 hrs. after birth. Conclusions : development in F of conjugation with glucose and xylose seems to parallel that of glucuronidation, and the proportions of the 3 sugar conjugates formed in newborns and adults are comparable. However, the proportion of diconjugates in bile of F is smaller than in bile of adults. Also, our findings suggest that initiation of BR conjugation in P and F occurs at birth and is independent of gestational age.

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