Sánchez-Gutiérrez J C, Lechuga C G, Sánchez-Arias J A, Samper B, Felíu J E
Servicio de Endocrinología Experimental, Hospital Puerta de Hierro, Madrid, Spain.
Endocrinology. 1995 May;136(5):1877-84. doi: 10.1210/endo.136.5.7720633.
Genetically obese (fa/fa) Zucker rats show oral glucose intolerance, an alteration that has been attributed at least in part to an impaired suppression of hepatic glucose output after the ingestion of glucose. In this work, we studied the influence of different concentrations of glucose (2.5-30 mM) on gluconeogenesis from a mixture of [14C]lactate-pyruvate as well as on fructose 2,6-bisphosphate levels, pyruvate kinase activity, and flux through the reaction catalyzed by 6-phosphofructo-1-kinase, in hepatocytes isolated from fed obese (fa/fa) or lean (Fa/-) rats. In hepatocytes isolated from lean rats, incubation with increasing concentrations of glucose caused a dose-dependent inhibition of gluconeogenesis (5.02 +/- 0.54 and 1.82 +/- 0.33 mumol lactate converted to glucose/g cells.20 min in hepatocytes incubated in the presence of 2.5 and 30 mM glucose, respectively; n = 4 experiments; P < 0.01) together with a significant elevation of the fructose 2,6-bisphosphate content and a stimulation of the flux through 6-phosphofructo-1-kinase reaction. Glucose also provoked a dose-dependent activation of pyruvate kinase in the absence of changes in the cellular concentration of cAMP. In liver cells from obese animals, gluconeogenesis was not significantly modified by raising the glucose concentration in the incubation medium (1.26 +/- 0.11 and 0.83 +/- 0.14 mumol lactate converted to glucose/g cells.20 min in hepatocytes incubated with 2.5 and 30 mM glucose, respectively; n = 4 experiments; P = 0.11) despite significant increases in both fructose 2,6-bisphosphate levels and flux through the 6-phosphofructo-1-kinase reaction. In these cells, pyruvate kinase was only slightly activated by high glucose concentrations. These results indicate that, unlike fructose 2,6-bisphosphate levels and flux through the 6-phosphofructo-1-kinase reaction, hepatic gluconeogenesis is unresponsive to high glucose concentrations in genetically obese (fa/fa) rats.
遗传性肥胖（fa/fa）的 Zucker 大鼠表现出口服葡萄糖不耐受，这种改变至少部分归因于摄入葡萄糖后肝脏葡萄糖输出抑制受损。在这项研究中，我们研究了不同浓度的葡萄糖（2.5 - 30 mM）对从[14C]乳酸 - 丙酮酸混合物生成糖异生的影响，以及对果糖 2,6 - 二磷酸水平、丙酮酸激酶活性和通过 6 - 磷酸果糖 - 1 - 激酶催化反应的通量的影响，这些实验是在从喂食后的肥胖（fa/fa）或瘦（Fa/-）大鼠分离的肝细胞中进行的。在从瘦大鼠分离的肝细胞中，用浓度不断增加的葡萄糖孵育会导致糖异生呈剂量依赖性抑制（在分别存在 2.5 和 30 mM 葡萄糖的情况下孵育的肝细胞中，每克细胞 20 分钟内将 5.02 ± 0.54 和 1.82 ± 0.33 μmol 乳酸转化为葡萄糖；n = 4 个实验；P < 0.01），同时果糖 2,6 - 二磷酸含量显著升高，并且通过 6 - 磷酸果糖 - 1 - 激酶反应的通量受到刺激。在细胞内 cAMP 浓度没有变化的情况下，葡萄糖还引起了丙酮酸激酶的剂量依赖性激活。在肥胖动物的肝细胞中，尽管果糖 2,6 - 二磷酸水平和通过 6 - 磷酸果糖 - 1 - 激酶反应的通量都显著增加，但在孵育培养基中提高葡萄糖浓度并没有显著改变糖异生（在分别用 2.5 和 30 mM 葡萄糖孵育的肝细胞中，每克细胞 20 分钟内将 1.26 ± 0.11 和 0.83 ± 0.14 μmol 乳酸转化为葡萄糖；n = 4 个实验；P = 0.11）。在这些细胞中，高葡萄糖浓度仅轻微激活丙酮酸激酶。这些结果表明，与果糖 2,6 - 二磷酸水平和通过 6 - 磷酸果糖 - 1 - 激酶反应的通量不同，在遗传性肥胖（fa/fa）大鼠中，肝脏糖异生对高葡萄糖浓度无反应。
