Intestinal amino acid metabolism in neonates.

The portal-drained viscera (stomach, intestine, pancreas and spleen) have a much higher rate of both energy expenditure and protein synthesis than can be estimated on the basis of their weight. A high utilization rate of dietary nutrients by the portal-drained viscera might result in a low systemic availability which determines whole-body growth. From studies in our multiple catheterized piglet model, we conclude that more than half of the dietary protein intake is utilized within the portal-drained viscera and that amino acids are a major fuel source for the visceral organs. Specific stable isotope studies reveal that there are large differences in the utilization rate amongst the different amino acids. The majority of the results obtained from the piglet studies can be extrapolated to the human (preterm) infant. First-pass, splanchnic uptake of lysine and threonine differ substantially, while non-essential amino acids are oxidized to a great extend in the human gut. Overall, these studies indicate that gut amino acid metabolism has a great impact on systemic availability and hence growth in the neonate.