Bile acid concentrations in serum and duodenal aspirates of healthy preterm infants: effects of gestational and postnatal age.

In 41 healthy human-milk-fed preterm infants the preprandial total bile acid (BA) concentrations in serum and duodenal juice were simultaneous measured during the first 60 days of life. The infants were subdivided into four groups according to their gestational age: 6 infants with a gestational age of 27 and 28 weeks, 7 infants with a gestational age of 29 and 30 weeks, 21 infants with a gestational age of 31 and 32 weeks and 7 infants with a gestational age of 33 and 34 weeks. The BA levels were enzymatically determined using 3-alpha-hydroxysteroid dehydrogenase. In the duodenal juice, cholic acid (CA), chenodeoxycholic acid (CDCA), deoxycholic acid and lithocholic acid were separately quantified by thin-layer chromatography. During the first month of life, the serum BA concentrations increased significantly with postnatal age (p < 0.01) but remained nearly constant during the second month of life. In the duodenal aspirates, the BA concentrations increased continuously up to the end of the observations period (p < 0.001). In the duodenal aspirates, the CA/CDCA ratio was high immediately after birth and decreased significantly with increasing postnatal age (p < 0.001). During the first weeks of life, the BA levels were preferentially conjugated with taurine, but in spite of the taurine-rich diet during the whole observation period the taurine/glycine ratio decreased with postnatal age (p < 0.001). In all samples of duodenal juice, the sum of primary BA was > 98% of total 3-alpha-hydroxy-BA. These data indicate that the establishment of an intestinal microbial flora necessary for intestinal BA transformation and the development of the enterohepatic BA circulation lasts some months of postnatal life. The serum BA concentration reflects hepatic synthesis, intestinal absorption, renal excretion and hepatocellular transport into bile in a very complex way which may limit the diagnostic value of serum BA during this time. Additionally, a duodenal BA concentration below 4 mmol/l, as found in this study during the first 2 weeks of life, may be of clinical importance due to its possible effects on fat absorption.