Bilirubin‐IX α and ‐IX β pigments, coproporphyrins and bile acids in meconium and stools from full‐term and preterm neonates during the first month of life

Abstract

Individual bilirubin pigments in the excreta were quantitated by newly developed methods. In meconium, bilirubin‐IX β predominated, whereas bilirubin‐IXγ and ‐IXδ remained undetectable. The daily excretion of bilirubin‐IXα plus ‐IXβ was 0.03–1.00 and 0.04–2.00 μmoles kg1 of birthweight in preterm and full‐term infants, respectively. The ratio of bilirubin‐IXα to ‐ IXβ 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‐IXβ disappeared within the first week in those with gestational age ± 31 wk but more slowly in the very preterm group. The ratio of monoconjugated to diconjugated bilirubin‐IXα was 4 to 5 in full‐term infants, 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‐IXα and β‐glucuronidase was observed. The daily coproporphyrin excretion fell from a median of 500 μg on day 1 to below 20 μg from day 7 onwards; this decrease correlated with that of bilirubin‐IXβ. The daily 3α‐hydroxylated bile 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 synthesis. Conclusion: Both zinc coproporphyrin and bilirubin‐IXβ are characteristic compounds of human meconium, diconjugated bilirubin‐IXα is low or absent in meconium of very preterm infants, and faecal and serum bile acids are high.

Bilirubin in clinical practice: a review

“…This results in the formation of other isomers; some can be detected in body fluids, although always in small amounts or under special conditions. The IXβ isomer is present in neonatal urine and in meconium (5), whereas the IXβ and IXγ isomers have been detected in Gunn rat bile (6). Because intramolecular hydrogen bonds cannot be formed in these isomers, they are more hydrophilic, and appear in urine or bile as an unconjugated pigment.…”

Excretion of biliary compounds during intrauterine life

“…Regarding bile pigments, although the IXβ isomer of bilirubin constitutes only a small fraction of the total amount produced in the fetus [33] , this more water-soluble isomer is the most abundant isomer found in fetal gallbladder bile and meconium [34,35] . The reason for this is two-fold: (1) bilirubin IXβ cannot easily cross the placenta; and (2) it can be excreted into bile without previous conjugation with glucuronic acid [36] .…”

Biochemical Intestinal Parameters in Germ‐free Minipigs and Rats and in Ex‐germ‐free Minipigs and Rats Monoassociated with Escherichia coli

“…Therefore, we could speculate that the values may derive from breakdown of pre‐term bilirubin in young pigs that interfere with our spectrophotometric method. It is well known that foetal bilirubins are chemically different from bilirubin in infants and adults and that foetal bilirubin might be excreted for several days (Aziz et al., 2001). More sophisticated and sensitive methods are required to elucidate the bilirubin metabolism in newborn and young mammals, including pigs (Midtvedt, 2001).…”