DETERMINATION OF KREBS CYCLE METABOLIC CARBON EXCHANGE INVIVO AND ITS USE TO ESTIMATE THE INDIVIDUAL CONTRIBUTIONS OF GLUCONEOGENESIS AND GLYCOGENOLYSIS TO OVERALL GLUCOSE OUTPUT IN MAN
DETERMINATION OF KREBS CYCLE METABOLIC CARBON EXCHANGE INVIVO AND ITS USE TO ESTIMATE THE INDIVIDUAL CONTRIBUTIONS OF GLUCONEOGENESIS AND GLYCOGENOLYSIS TO OVERALL GLUCOSE OUTPUT IN MAN
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DOI：
10.1172/jci113206
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发表时间：
1987-11-01
影响因子：
15.9
通讯作者：
GERICH, J
中科院分区：
文献类型：
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作者：
CONSOLI, A;KENNEDY, F;GERICH, J
由于克雷布斯循环碳交换和无法测量线粒体内前体特异性活性，目前的同位素方法低估了体内糖异生。因此，我们应用了一种新的同位素方法，从理论上克服了这些限制，并允许量化克雷布斯循环碳交换以及糖异生和糖原分解对总葡萄糖输出的个体贡献。[6-3H]葡萄糖输注，测量总葡萄糖输出量；注入[2-14C]醋酸酯，追踪磷酸烯醇丙酮酸糖异生，计算Katz提出的Krebs循环碳交换。血浆[14C]3- oh -丁酸比活性用于估计线粒体内乙酰辅酶A （CoA）的比活性，最后血浆葡萄糖14C比活性与计算的细胞内磷酸烯醇丙酮酸14C比活性的比值用于确定糖异生和糖原分解对总葡萄糖输出的相对贡献。使用这种方法，发现乙酰辅酶a进入克雷布斯循环的速度分别是丙酮酸的两倍（吸收后受试者）和三倍（禁食2 1/2天受试者）。吸收后受试者的糖异生(3.36 .+-。0.20 .mu。Mol /kg / min)占28。在禁食2 1/2 d的受试者中，总葡萄糖输出增加了2倍（P < 0.01），占总葡萄糖输出的97%。吸收后受试者的糖原溶解平均为8.96±。0.40 .mu。Mol /kg / min，降至0.34 +-。0.08 .mu。mol/kg / min （P < 0.01）。由于这些结果与先前报道的基于内脏底物平衡和连续肝活检糖原含量测定的糖异生和糖原分解值一致，我们得出结论，本文应用的同位素方法提供了一种准确的、无创的体内糖异生和糖原分解测量方法。
Current isotopic approaches underestimate gluconeogenesis in vivo because of Krebs cycle carbon exchange and the inability to measure intramitochondrial precurosr specific activity. We therefore applied a new isotopic approach that theoretically overcomes these limitations and permits quantification of Krebs cycle carbon exchange and the individual contributions of gluconeogenesis and glycogenolysis to overall glucose output. [6-3H]Glucose was infused to measure overall glucose output; [2-14C]acetate was infused to trace phosphoenolpyruvate gluconeogenesis and to calculate Krebs cycle carbon exchange as proposed by Katz. Plasma [14C]3-OH-butyrate specific activity was used to estimate intramitochondrial acetyl coenzyme A (CoA) specific activity, and finally the ratio between plasma glucose 14C-specific activity and the calculated intracellular phosphoenolpyruuate 14 C specific activity was used to determine the relative contributions of gluconeogenesis and glycogenolysis to overall glucose output. Using this approach, acetyl CoA was found to enter the Krebs cycle at twice (postabsorptive subjects) and three times (2 1/2-d fasted subjects) the rate of pyruvate, respectively. Gluconeogenesis in postabsorptive subjects (3.36 .+-. 0.20 .mu.mol/kg per min) accounted for 28 .+-. 2% of overall glucose output and increased twofold in subjects fasted for 2 1/2-d (P < 0.01), accounting for > 97% of overall glucose output. Glycogenolysis in postabsorptive subjects averaged 8.96 .+-. 0.40 .mu.mol/kg per min and decreased to 0.34 .+-. 0.08 .mu.mol/kg per min (P < 0.01) after a 2 1/2-d fast. Since these results agree well with previously reported values for gluconeogenesis and glycogenolysis based on determinations of splanchnic substrate balance and glycogen content of serial liver biopsies, we conclude that the isotopic approach applied herein provides an accurate, noninvasive measurement of gluconeogenesis and glycogenolysis in vivo.