Biolo Gianni, Zorat Francesca, Antonione Raffaella, Ciocchi Beniamino
Department of Clinical, Morphological and Technological Sciences, University of Trieste, Trieste, Italy.
Int J Biochem Cell Biol. 2005 Oct;37(10):2169-79. doi: 10.1016/j.biocel.2005.05.001.
Glutamine is primarily synthesized in skeletal muscle and enables transfer of nitrogen to splanchnic tissues, kidneys and immune system. Discrepancy between increasing rates of glutamine utilization at whole body level and relative impairment of de novo synthesis in skeletal muscle leads to systemic glutamine deficiency and characterizes critical illness. Glutamine depletion at whole body level may contribute to gut, liver and immune system disfunctions, whereas its intramuscular deficiency may directly contribute to lean body mass loss. Severe intramuscular glutamine depletion also develops because of outward transport system upregulation, which is not counteracted by increased de novo synthesis. The negative impact of systemic glutamine depletion on critically ill patients is suggested both by the association between a lower plasma glutamine concentration and poor outcome and by a clear clinical benefit after glutamine supplementation. Enteral glutamine administration preferentially increases glutamine disposal in splanchnic tissues, whereas parenteral supplementation provides glutamine to the whole organism. Nonetheless, systemic administration was ineffective in preventing muscle depletion, due to a relative inability of skeletal muscle to seize glutamine from the bloodstream. Intramuscular glutamine depletion could be potentially counteracted by promoting de novo glutamine synthesis with pharmacological or nutritional interventions.
谷氨酰胺主要在骨骼肌中合成，并能将氮转运至内脏组织、肾脏和免疫系统。全身水平谷氨酰胺利用率的增加速率与骨骼肌中从头合成的相对受损之间的差异导致全身性谷氨酰胺缺乏，并成为危重病的特征。全身水平的谷氨酰胺消耗可能导致肠道、肝脏和免疫系统功能障碍，而其肌肉内缺乏可能直接导致瘦体重损失。严重的肌肉内谷氨酰胺消耗也由于向外转运系统上调而发生，而这种上调并未被增加的从头合成所抵消。较低的血浆谷氨酰胺浓度与不良预后之间的关联以及补充谷氨酰胺后明显的临床益处均提示全身性谷氨酰胺消耗对危重病患者有负面影响。肠内给予谷氨酰胺优先增加内脏组织中谷氨酰胺的处置，而肠外补充则为整个机体提供谷氨酰胺。尽管如此，全身给药在预防肌肉消耗方面无效, 这是因为骨骼肌相对无法从血液中摄取谷氨酰胺。通过药物或营养干预促进谷氨酰胺的从头合成可能会抵消肌肉内谷氨酰胺的消耗。
