Transformation of bilirubin in gastrointestinal tract and its relationship to neonatal icterus

The object of the study was the transformation of bilirubin in the neonatal digestive tract with special reference to enterohepatic circulation of nonconjugated bilirubin and its consequences. The application of biochemical and chromatographic methods showed that bilirubin excreted by neonatal livers was qualitatively distinct from that excreted by adult livers. Already in the first meconium practically all bilirubin conjugated with glucuronic acid was hydrolyzed, which means ample availability of nonconjugated bilirubin for its reresorption by intestines. The enterohepatic circulation of nonconjugated bilirubin could indirectly be demonstrated by early elimination of nonconjugated bilirubin reservoir - meconium - from the digestive tract. This resulted in a significant reduction of bilirubinaemia. It could be shown that in newborns with hyperbilirubinaemia alterations of structure of bilirubin excreted into bile due to phototherapy occurred. This finding leads to an assumption that besides a favourable effect, apparently predominating in bilirubin degradation, phototherapy tends in an undesirable way to increase enteral reabsorption of nonconjugated bilirubin back in the circulation.