Bilirubin-IX alpha and -IX beta pigments, coproporphyrins and bile acids in meconium and stools from full-term and preterm neonates during the first month of life

Individual bilirubin pigments in the excreta were quantitated by newly deve loped methods. In meconium, bilirubin-IX beta predominated, whereas bilirub in-IX gamma and -IX delta remained undetectable. The daily excretion of bil irubin-IX alpha plus -IX beta was 0.03-1.00 and 0.04-2.00 mu moles kg(-1) o f birthweight in preterm and full-term infants, respectively. The ratio of bilirubin-IX alpha to -IX beta in meconium was 0.25 +/- 0.34, 0.32 +/- 0.30 and 0.46 +/- 0.55 in newborns of gestational ages below 30, from 31 to 36 and above 36 wk, respectively. The predominance of bilirubin-IX beta disapp eared within the first week in those with gestational age greater than or e qual to 31 wk but more slowly in the very preterm group. The ratio of monoc onjugated to diconjugated bilirubin-IX alpha. was 4 to 5 in full-term infan ts, whereas this ratio was only reached after 1 mo in preterm infants. The ratio of glucuronide or glucoside to xyloside varied widely, independent of gestational age. No correlation between faecal UCB-IX alpha and beta -gluc uronidase was observed. The daily coproporphyrin excretion fell from a medi an of 500 mug on day 1 to below 20 mug from day 7 onwards; this decrease co rrelated with that of bilirubin-IX beta. The daily 3 alpha -hydroxylated bi le acid loss in the excreta was two- to fivefold higher than in the adult; this, together with the higher neonatal serum levels (12-90 nmoles ml(-1)), indicates an immature intestinal reabsorption and an enhanced bile acid sy nthesis. Conclusion: Both zinc coproporphyrin and bilirubin-IX beta are characterist ic compounds of human meconium, diconjugated bilirubin-IX alpha is low or a bsent in meconium of very preterm infants, and faecal and serum bile acids are high.