Plasma amino acids in preterm infants after a feed of human milk or formula.

Prefeeding and sequential postprandial plasma amino acid concentrations were measured in 31 healthy preterm infants with gestational ages between 33 and 37 weeks at the ages of 4 to 12 days, to characterize changes after quantitatively and qualitatively different protein loads. All infants had previously been fed with human milk. The infants received a normal feed of pooled human milk (true protein 0.8 gm/dl) or of adapted or nonadapted milk formula (protein 1.5 gm/dl) from a bottle. The concentrations of all essential and several nonessential amino acids, including arginine and ornithine, rose sharply in plasma. Glycine decreased, and alanine increased slowly. Postprandial alterations in plasma total amino acids seemed to reflect the protein content of the different milks. In preterm infants, fed at three- to four-hour intervals, plasma amino acid concentrations fluctuate continuously. Thus in long-term studies and in screening, samples should be taken immediately before feeds. Postprandial plasma amino acid measurements may prove to be a useful means for testing the infant's ability to handle the protein or individual amino acid loads in various feeds.