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Unconjugated and conjugated bilirubin pigments during perinatal development. I. Studies on rat serum and intestine
Insights
Bilirubin conjugation and excretion develop rapidly in rat intestines during late fetal development. Neonatal rats show a predominant excretory defect, unlike human infants.
Area of Science:
- Biochemistry
- Developmental Biology
- Neonatal Physiology
Background:
- Bilirubin metabolism and excretion pathways are critical for preventing hyperbilirubinemia.
- Understanding perinatal bilirubin handling is essential for identifying neonatal jaundice causes.
Purpose of the Study:
- To investigate the developmental changes in bilirubin conjugation and excretion in rats during the perinatal period.
- To compare bilirubin metabolism in fetal, neonatal, and adult rats.
Main Methods:
- Quantification of unconjugated, mono-, and diconjugated bilirubin in rat plasma and intestinal tissue.
- Analysis of bilirubin levels at various developmental stages (18-day fetus to 1 day postnatal).
Main Results:
- Bilirubin conjugates appear in the fetal intestine by day 18, with rapid increases postnatally.
- Intestinal bilirubin conjugation/excretion develops significantly in the final days of gestation.
- Neonatal rat plasma shows elevated total bilirubin with a higher conjugated proportion, suggesting an excretory defect.
Conclusions:
- Intestinal bilirubin conjugation and excretion mature rapidly during late fetal development in rats.
- Neonatal rats exhibit a primary excretory defect for bilirubin, contrasting with human physiology.
- Transplacental bilirubin clearance appears inefficient in rats during late gestation.
Abstract:
Unconjugated, mono- and diconjugated bilirubin was measured in rat plasma and intestine during perinatal development. Bilirubin monoconjugates were present in the intestines of 18-day-old fetuses, while diconjugates appeared on the 20th day. The concentration of conjugates increased rapidly, reaching 312 mumol/g of intestinal tissue 1 day after birth. The absolute concentration of unconjugated bilirubin increased in parallel. On the 18th day of fetal life, about 80% of the pigment in the intestine was unconjugated, while conjugates largely predominated from the 20th day onwards. Conjugation and/or excretion of bilirubin in the intestine seems therefore to develop rapidly during the last days of life. The plasma concentration of total bilirubin in 18-day-old fetuses was about 2-3 times higher than in adult serum, and it increased slightly during the following days. 2-7% of the pigment was conjugated. Transplacental clearance of bilirubin seems therefore to be deficient in this species. On the 1st day of extrauterine life, bilirubin concentration increased sharply in plasma, reaching 14.76 mumol/l, 38% in the conjugated form. This finding suggests that, unlike humans, an excretory defect is predominant in the neonatal rat.