Splanchnic oxidation is the major metabolic fate of dietary glutamate in enterally fed preterm infants.

The intestine is a major site of amino acid metabolism, especially in neonates. The energy needed for the metabolic processes in neonatal animals is derived from dietary glucose and amino acids. No data are available showing that dietary amino acids function as intestinal fuel source in human neonates as well. We hypothesized that preterm infants show a high splanchnic first-pass glutamate metabolism and the primary metabolic fate of glutamate is oxidation. Five preterm infants (birth weight 1.2+/-0.2 kg, gestational age 29+/-1 wk) were studied by dual tracer ([U-(13)C]glutamate and [D3]glutamate) techniques on two study days (within postnatal d 14-19). Splanchnic and whole-body glutamate kinetics were assessed by plasma isotopic enrichment of [U-(13)C]glutamate and [D3]glutamate and breath CO2 enrichment. Fractional first-pass glutamate uptake was 77+/-18% on d 1, and 70+/-7% on d 2, mean 74+/-13%. Almost all (86+/-7%) of the glutamate used in the first pass is directed toward oxidation. There is a high splanchnic fractional first-pass uptake and a high oxidation rate of glutamate in preterm infants. Glutamate is an important source of energy for the splanchnic tissues in preterm infants receiving full enteral feeding.