Our results support this model and suggest that ManNAc can be further 4-hydroxyephedrine-hydrochloride epimerized by Renbp to GlcNAc. The brain incorporates a large amount of Sia during development which begins in utero but continues postnatally. Postnatally the sources and their relative contributions of Sia for use in the brain or from the diet) are currently unknown. The Sia transporter Slc17a5 has been reported to be expressed throughout the adult rodent brain and during embryonic development highest levels are seen in the central and peripheral nervous system. Also radioactivity from radiolabelled Sia administered to suckling animals can reach the brain although the biochemical pathway followed is not known. Such results have led to the suggestion that the brain gets at least some of its Sia from exogenous sources. Our gene expression results in the neonatal brain do not provide additional evidence for a significant use of exogenous Sia during this time. Studying the brain as a whole as was done here may have masked important regional differences where significant use of exogenously supplied Sia occurs. The liver may be a source of Sia for other tissues and organs. In the liver the epimerase activity of GNE, the rate limiting enzyme of Sia synthesis, increased during the first week of lactation in parallel to the milk Sia concentration. Whether milk Sia is the stimulus for this activity increase is unknown however Wang et al. have previously shown that piglets D-Pinitol provided a diet enriched in Sia increased expression of GNE mRNA in both the liver and hippocampus. At present we do not know if rat liver GNE gene expression parallels that of its enzymatic activity during early development. Ingested milk oligosaccharides are also excreted unaltered and in significant amounts in the urine and feces. In human infants about 0.5 to 1% of ingested milk oligosaccharides were reported to be excreted in urine. In rats we also found part of the ingested sialyllactose in urine and estimated that maximally 1% of ingested sialyllactose was excreted into urine. A possible answer to both questions is their decoy function.