The effect of feeding route (i.v. or oral) on the protein metabolism of the neonate.

We have examined the effect of the route of feeding (intravenous versus enteral) on the protein metabolism of postsurgical human neonates. Twelve infants, birth weight 2.5 +/- 0.2 kg, gestational age 38 +/- 1 wk, were studied. The IV study was carried out 1-4 days after surgery at a postnatal age of 14 days and a weight of 2.6 +/- 0.2 kg. The repeat (oral) study was carried out 16 days later. Protein intakes were similar during both studies (2.7 g/kg/d). Energy intakes were within the requirement range for age and feeding route and were: IV, 85 +/- 4 kcal/kg/d; oral, 111 +/- 7 kcal/kg/d. Whole body protein metabolism was studied using a continuous infusion of 15N-glycine. Amino nitrogen flux, protein synthesis, and breakdown were 40% higher during the enteral than the IV studies (p less than 0.001). Skeletal muscle degradation was investigated by measuring urinary excretion of creatinine and N-T-methylhistidine. No differences were detected due to feeding route. We suggest that the differences seen in whole body protein turnover rates reflect the rapid growth and development of the gut in the enterally (rather than the IV) fed infant.