Ferrando A A, Williams B D, Stuart C A, Lane H W, Wolfe R R
Biomedical Operations and Research Branch, National Aeronautics and Space Administration, Johnson Space Center, Houston, Texas, USA.
JPEN J Parenter Enteral Nutr. 1995 Jan-Feb;19(1):47-54. doi: 10.1177/014860719501900147.
This study reports the effects of ingesting branched-chain amino acids (leucine, valine, and isoleucine) on protein metabolism in four men.
To calculate leg protein synthesis and breakdown, we used a new model that utilized the infusion of L-[ring-13C6]phenylalanine and the sampling of the leg arterial-venous difference and muscle biopsies. In addition, protein-bound enrichments provided for the direct calculation of muscle fractional synthetic rate. Four control subjects ingested an equivalent amount of essential amino acids (threonine, methionine, and histidine) to discern the effects of branched-chain amino acid nitrogen vs the effects of essential amino acid nitrogen. Each drink also included 50 g of carbohydrate.
Consumption of the branched-chain and the essential amino acid solutions produced significant threefold and fourfold elevations in their respective arterial concentrations. Protein synthesis and breakdown were unaffected by branched-chain amino acids, but they increased by 43% (p < .05) and 36% (p < .03), respectively, in the group consuming the essential amino acids. However, net leg balance of phenylalanine was unchanged by either drink. Direct measurement of protein synthesis by tracer incorporation into muscle protein (fractional synthetic rate) revealed no changes within or between drinks. Whole-body phenylalanine flux was significantly suppressed by each solution but to a greater extent by the branched-chain amino acids (15% and 20%, respectively) (p < .001).
These results suggest that branched-chain amino acid ingestion suppresses whole-body proteolysis in tissues other than skeletal muscle in normal men.
本研究报告了摄入支链氨基酸（亮氨酸、缬氨酸和异亮氨酸）对四名男性蛋白质代谢的影响。
为了计算腿部蛋白质合成与分解，我们使用了一种新模型，该模型利用L-[环-13C6]苯丙氨酸输注以及腿部动静脉差值采样和肌肉活检。此外，蛋白质结合富集用于直接计算肌肉分数合成率。四名对照受试者摄入等量的必需氨基酸（苏氨酸、蛋氨酸和组氨酸），以区分支链氨基酸氮的影响与必需氨基酸氮的影响。每种饮品还包含50克碳水化合物。
饮用支链氨基酸溶液和必需氨基酸溶液后，它们各自的动脉浓度显著升高了三倍和四倍。蛋白质合成与分解不受支链氨基酸影响，但在饮用必需氨基酸的组中，蛋白质合成和分解分别增加了43%（p < .05）和36%（p < .03）。然而，两种饮品均未改变腿部苯丙氨酸的净平衡。通过示踪剂掺入肌肉蛋白质直接测量蛋白质合成（分数合成率）显示，饮品内部或之间均无变化。每种溶液均显著抑制全身苯丙氨酸通量，但支链氨基酸的抑制作用更大（分别为15%和20%）（p < .001）。
这些结果表明，在正常男性中，摄入支链氨基酸可抑制骨骼肌以外组织的全身蛋白水解。
