Splanchnic metabolism of ingested amino acids in neonates

Neonates typically show rapid growth. Nutrient absorption in the neonatal period is higher than during any other time in life so as to meet the requirements for this rapid growth. Generally, nutrients are administered enterally, and in the past the gut was considered to absorb and digest these nutrients without major metabolism. Recent animal and human work has, however, revealed that the intestine and other splanchnic tissues contribute significantly to whole-body metabolism, and have their own specific functions. This review focuses on these observations. The splanchnic tissues take up greatly different proportions of each of the amino acids, ranging from 80-100% for threonine and several nonessential amino acids to 15-30% for lysine. The metabolic fates of the utilized substrates differ as well. Some are predominantly used for constitutive protein synthesis, others for energy generation or for formation of (glyco-)proteins that are secreted into the lumen. Glucose appears to be the major contributor to energy generation, but amino acids are important as well. Both animal and human studies have shown that the intestine uses substantial amounts of dietary amino acids. This has several implications for the nutritional needs of infants to maintain growth, especially during times of inadequate enteral nutrition