Wu G
Departments of Animal Science, Medical Physiology, and Veterinary Anatomy and Public Health, and Faculty of Nutrition, Texas A&M University, College Station, TX 77843, USA.
J Nutr. 1998 Aug;128(8):1249-52. doi: 10.1093/jn/128.8.1249.
The small intestine is not only responsible for terminal digestion and absorption of nutrients, but it also plays an important role in catabolism of arterial glutamine and dietary amino acids. Most of glutamine and almost all of glutamate and aspartate in the diet are catabolized by small intestinal mucosa, and CO2 accounts for 56-64% of their metabolized carbons. The small intestinal mucosa also plays an important role in degrading arginine, proline and branched-chain amino acids, and perhaps methionine, lysine, phenylalanine, threonine, glycine and serine in the diet, such that 30-50% of these dietary amino acids are not available to extraintestinal tissues. Dietary amino acids are major fuels for the small intestinal mucosa and are essential precursors for intestinal synthesis of glutathione, nitric oxide, polyamines, purine and pyrimidine nucleotides, and amino acids (alanine, citrulline and proline), and are obligatory for maintaining intestinal mucosal mass and integrity. Because intestinal amino acid catabolism plays an important role in modulating dietary amino acid availability to extraintestinal tissues, it has important implications for the utilization efficiency of dietary protein and amino acids in animals and humans.
小肠不仅负责营养物质的终末消化和吸收，还在动脉谷氨酰胺和膳食氨基酸的分解代谢中发挥重要作用。膳食中的大部分谷氨酰胺以及几乎所有的谷氨酸和天冬氨酸都由小肠黏膜进行分解代谢，二氧化碳占其代谢碳的56 - 64%。小肠黏膜在分解膳食中的精氨酸、脯氨酸和支链氨基酸，或许还有蛋氨酸、赖氨酸、苯丙氨酸、苏氨酸、甘氨酸和丝氨酸方面也发挥着重要作用，以至于这些膳食氨基酸中有30 - 50%无法被肠外组织利用。膳食氨基酸是小肠黏膜的主要燃料，是肠道合成谷胱甘肽、一氧化氮、多胺、嘌呤和嘧啶核苷酸以及氨基酸（丙氨酸、瓜氨酸和脯氨酸）的必需前体，对于维持肠黏膜质量和完整性必不可少。由于肠道氨基酸分解代谢在调节膳食氨基酸对肠外组织的可利用性方面发挥重要作用，因此对动物和人类膳食蛋白质及氨基酸的利用效率具有重要意义。
