Almost all enteral aspartate is taken up in first-pass metabolism in enterally fed preterm infants

The intestine is a major site of amino acid metabolism, especially in neonates. Neonatal animals derive energy needed for metabolic processes from dietary glucose and amino acids. Rats were found to oxidize non-essential amino acids such as aspartate, glutamate and glutamine in the intestine at a high rate. We have previously found that glutamate and glucose are important sources of energy for the splanchnic tissues in fully fed preterm infants. However, no data are available on splanchnic aspartate metabolism in human preterm infants. In the present study we studied whole-body and splanchnic aspartate metabolism and determined the metabolic fate of aspartate. In eight, enterally fed, preterm infants (gestational age 31 weeks (wk)+/-3 SD, range: 26-34wk) splanchnic and whole-body aspartate kinetics were assessed by dual tracer ([U-(13)C]aspartate and [D(3)]aspartate) techniques. Splanchnic first-pass aspartate uptake was almost complete (77+/-15%). Almost all (80+/-9%) of the (13)C administered as [U-(13)C]aspartate used in first-pass was recovered as CO(2) in expired breath. The splanchnic tissues extract almost all of the dietary aspartate in preterm infants. The majority of the labeled carbon is recovered in expired breath, making it most likely that the sequestered carbon skeleton of aspartate is utilized for energy generation