Holecek Milan
Department of Physiology, Charles University School of Medicine, Hradec Králové, Czech Republic.
Nutrition. 2002 Feb;18(2):130-3. doi: 10.1016/s0899-9007(01)00767-5.
The branched-chain amino acids (BCAAs; valine, isoleucine, and leucine) are the major nitrogen source for glutamine and alanine synthesis in muscle. Synthesis of glutamine, alanine, and BCAA use is activated in critical illnesses such as in sepsis, cancer, and trauma. The use of glutamine often exceeds its synthesis, resulting in the lack of glutamine in plasma and tissues. In critical illness, resynthesis of BCAA from branched-chain keto acids is activated, particularly in hepatic tissue. The BCAA released to circulation may be used for protein synthesis or synthesis of alanine and glutamine. Glutamine and/or alanine infusion has an inhibitory effect on the breakdown of body proteins and decreases BCAA catabolism in postabsorptive control, endotoxemic, and irradiated rats. Decreased protein breakdown also was observed when glutamine synthesis was activated by ammonia infusion. In conclusion some favorable effects of BCAA supply can be explained by its role in the synthesis of glutamine and some positive effects of glutamine exogenous supply can be explained by its effect on metabolism of BCAA.
支链氨基酸（BCAAs；缬氨酸、异亮氨酸和亮氨酸）是肌肉中谷氨酰胺和丙氨酸合成的主要氮源。在脓毒症、癌症和创伤等危重症中，谷氨酰胺、丙氨酸的合成以及支链氨基酸的利用被激活。谷氨酰胺的利用常常超过其合成，导致血浆和组织中谷氨酰胺缺乏。在危重症中，从支链酮酸重新合成支链氨基酸被激活，尤其是在肝组织中。释放到循环中的支链氨基酸可用于蛋白质合成或丙氨酸和谷氨酰胺的合成。在禁食对照、内毒素血症和受辐照的大鼠中，输注谷氨酰胺和/或丙氨酸对机体蛋白质分解有抑制作用，并减少支链氨基酸分解代谢。当通过输注氨激活谷氨酰胺合成时，也观察到蛋白质分解减少。总之，支链氨基酸供应的一些有益作用可通过其在谷氨酰胺合成中的作用来解释，而谷氨酰胺外源供应的一些积极作用可通过其对支链氨基酸代谢的影响来解释。
