Glutamine Supplements in the Critically Ill
Glutamine Supplements in the Critically Ill
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危重病人的谷氨酰胺补充剂
DOI：
10.1177/014107680409700904
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发表时间：
2004
影响因子：
17.3
通讯作者：
J. Powell
中科院分区：
文献类型：
--
作者：
R. D'Souza;J. Powell
谷氨酰胺是一种五碳中性氨基酸，含有两个羧基，其中一个与氮结合，形成酰胺基。它是人体内含量最多的游离氨基酸在细胞外液中，它约占游离氨基酸库的25%，在骨骼肌中占60%以上一个70公斤的健康人体内含有80克谷氨酰胺，血液中谷氨酰胺的浓度为500 - 700毫摩尔/升。谷氨酰胺在正常生理中有许多功能——例如，它作为蛋白质合成的前体；它为精氨酸、嘌呤、嘧啶、核苷酸、谷胱甘肽和牛磺酸（后两种是重要的抗氧化剂）的合成提供氮；它将氨基氮输送到肠、肝和肾。1-3参与肾氨生成，在酸碱平衡中起关键作用胃肠道快速分裂的细胞（肠细胞、结肠细胞）和免疫系统的细胞（淋巴细胞、巨噬细胞）尤其依赖谷氨酰胺作为燃料谷氨酰胺可能通过改变细胞水化状态影响应激诱导的细胞外液的积累细胞水合作用的增加是合成代谢增殖信号，而细胞收缩是分解代谢和抗增殖信号。在正常情况下，谷氨酰胺很容易合成并储存在骨骼肌中，而少量的谷氨酰胺则在肝脏、肺和大脑中产生因为它可以由身体产生，所以它被认为是一种非必需氨基酸。然而，这并不适用于器官/组织需求过多的情况，如败血症和其他分解代谢应激急剧下降的状态在这种情况下，体内产生的谷氨酰胺不足以满足肠道、免疫系统、肝脏和肾脏增加的需求骨骼肌中的蛋白质分解，释放出大量谷氨酰胺，从而满足部分需求，谷氨酰胺成为一种有条件必需的氨基酸。谷氨酰胺耗竭的后果
Glutamine is a five-carbon neutral aminoacid containing two carboxyl groups one of which is bound to nitrogen, forming an amide group. It is the most abundant free aminoacid in the body.1 In the extracellular fluid it constitutes about 25% of the free aminoacid pool, in skeletal muscle more than 60%.1 A healthy 70 kg man contains 80 g of glutamine and the concentration of glutamine in his blood is 500– 700 mmol/L. Glutamine has numerous functions in normal physiology—for example, it acts as a precursor for protein synthesis; it provides the nitrogen for synthesis of arginine, purines, pyrimidines, nucleotides, glutathione and taurine (the last two being important antioxidants); and it transports amino-nitrogen to intestine, liver and kidney.1–3 With its involvement in renal ammoniagenesis it plays a key role in acid–base homoeostasis.2 Particularly reliant on glutamine as a fuel are the rapidly dividing cells of the gastrointestinal tract (enterocytes, colonocytes) and the immune system (lymphocytes, macrophages).3,4 Glutamine may affect stress-induced accumulation of extracellular fluid by changing the cellular hydration state.4 An increase in cellular hydration acts as an anabolic proliferative signal, whereas cell shrinkage is catabolic and anti-proliferative. Under normal circumstances glutamine is readily synthesized and stored in skeletal muscle whilst lesser amounts are produced in the liver, lungs and brain.1 Since it can be produced by the body it is regarded as a nonessential aminoacid. However, this does not apply to conditions of excessive organ/tissue demand such as sepsis and other states of catabolic stress declines greatly.4 In these circumstances, production of glutamine in the body is insufficient to meet the increased requirement by the gut, immune system, liver and kidneys.4 The demands are then met in part by protein breakdown in skeletal muscle, with release of large amounts of glutamine and glutamine becomes a conditionally essential aminoacid. CONSEQUENCES OF GLUTAMINE DEPLETION