Mithieux G
INSERM U. 449, Faculté de Médecine R.T.H. Laennec, rue Guillaume Paradin, F69372 Lyon Cédex 08, France.
Curr Opin Clin Nutr Metab Care. 2001 Jul;4(4):267-71. doi: 10.1097/00075197-200107000-00004.
Both glutamine and glucose are highly utilized by the small intestine in various animal species. They are, however, very partially oxidized, the major known fate of glucose being lactate and alanine, and that of glutamine being citrulline or proline. At variance with the current view that only the liver and kidney are gluconeogenic organs, because both are the only tissues to express the glucose-6 phosphatase gene, this gene is also expressed in the small intestine in rats and humans, and is strongly induced in insulinopenic states, such as fasting and diabetes. Under the latter conditions, the small intestine contributes 20-25% of whole-body endogenous glucose production. The main small intestine gluconeogenic substrate is glutamine and, to a lesser extent, glycerol. Accounting for these fluxes, the phosphoenolpyruvate carboxykinase gene is strongly induced in insulinopenia and, although up to now it had been considered absent from this tissue, the glycerokinase gene is expressed in the small intestine. The production of glucose by the small intestine may be acutely blunted upon insulin infusion. These new data also emphasize the central role of alanine aminotransferase in the coupling of glutamine and glucose metabolisms in the small intestine.
谷氨酰胺和葡萄糖在各种动物物种中均被小肠大量利用。然而，它们的氧化程度非常有限，已知葡萄糖的主要代谢产物是乳酸和丙氨酸，谷氨酰胺的主要代谢产物是瓜氨酸或脯氨酸。目前认为只有肝脏和肾脏是糖异生器官，因为只有这两个组织表达葡萄糖-6磷酸酶基因，但与这种观点不同的是，该基因在大鼠和人类的小肠中也有表达，并且在胰岛素缺乏状态（如禁食和糖尿病）下会被强烈诱导。在后者的情况下，小肠对全身内源性葡萄糖生成的贡献为20%-25%。小肠主要的糖异生底物是谷氨酰胺，其次是甘油。考虑到这些通量，磷酸烯醇式丙酮酸羧激酶基因在胰岛素缺乏时会被强烈诱导，并且尽管到目前为止一直认为该组织中不存在甘油激酶基因，但它在小肠中是有表达的。输注胰岛素后，小肠的葡萄糖生成可能会急剧减弱。这些新数据还强调了丙氨酸转氨酶在小肠谷氨酰胺和葡萄糖代谢偶联中的核心作用。
