Soler C, Soley M
Departament de Bioquímica i Fisiologia, Universität de Barcelona, Spain.
Biochem J. 1993 Sep 15;294 ( Pt 3)(Pt 3):865-72. doi: 10.1042/bj2940865.
Most reports on the effects of epidermal growth factor (EGF) on gluconeogenesis have indicated that such effects depend on the substrate used and are only observable after a lag time of 30-40 min. Recently, an immediate and transient effect of EGF on glucose synthesis was described in a perfused liver system. Here we extend the study of the effect of EGF on gluconeogenesis to isolated hepatocytes from fasted rats. The delayed effect of EGF on gluconeogenesis was studied by adding the substrate 40 min after the peptide. Under these conditions EGF increased glucose synthesis from pyruvate, decreased it when the substrate was lactate or glycerol and did not modify gluconeogensis from fructose or dihydroxyacetone. EGF did not affect the metabolic flux through glycolysis, determined as the production of lactate+pyruvate from 30 mM glucose. Furthermore, EGF did not modify the metabolic flux through pyruvate kinase, determined as the production of lactate+pyruvate from 1 mM dihydroxyacetone. The differing effects of EGF on gluconeogenesis depending on the substrate used can be explained by the effects of EGF on the cytosolic redox state (measured as the lactate/pyruvate ratio). About 20 min after the addition of EGF, the mitochondrial redox state (measured as the 3-hydroxybutyrate/acetoacetate ratio) decreased. This effect of EGF was blocked by ammonium, which also abolished the effect of the peptide on gluconeogenesis. Thus the effect of EGF at the mitochondrial level appears to be necessary for its effects on gluconeogenesis. Taken together, our results indicate that the delayed effects of EGF on gluconeogenesis are secondary to the effects of the peptide at both the mitochondrial and cytosolic levels. In addition to these delayed effects, we observed that EGF rapidly and transiently stimulated glucose synthesis from lactate, decreased the cytosolic redox state and increased oxygen consumption. All of these rapid effects required the presence of extracellular calcium and disappeared in the presence of rotenone, suggesting that this rapid effect of EGF on gluconeogenesis is secondary to the stimulation of mitochondrial respiration.
大多数关于表皮生长因子（EGF）对糖异生作用的报告表明，这种作用取决于所使用的底物，并且只有在30 - 40分钟的延迟时间后才能观察到。最近，在灌注肝脏系统中描述了EGF对葡萄糖合成的即时和短暂作用。在此，我们将EGF对糖异生作用的研究扩展到来自禁食大鼠的分离肝细胞。通过在肽添加40分钟后添加底物来研究EGF对糖异生的延迟作用。在这些条件下，EGF增加了丙酮酸生成葡萄糖的合成，当底物是乳酸或甘油时则降低了葡萄糖合成，并且对果糖或二羟基丙酮的糖异生没有影响。EGF不影响通过糖酵解的代谢通量，通过从30 mM葡萄糖生成乳酸 + 丙酮酸来确定。此外，EGF不改变通过丙酮酸激酶的代谢通量，通过从1 mM二羟基丙酮生成乳酸 + 丙酮酸来确定。EGF对糖异生的不同作用取决于所使用的底物，可以通过EGF对细胞溶质氧化还原状态（以乳酸/丙酮酸比值衡量）的作用来解释。添加EGF约20分钟后，线粒体氧化还原状态（以3 - 羟基丁酸/乙酰乙酸比值衡量）降低。EGF的这种作用被铵阻断，铵也消除了该肽对糖异生的作用。因此，EGF在线粒体水平的作用似乎是其对糖异生作用所必需的。综上所述，我们的结果表明，EGF对糖异生的延迟作用是该肽在线粒体和细胞溶质水平作用的继发效应。除了这些延迟作用外，我们观察到EGF迅速且短暂地刺激了乳酸生成葡萄糖的合成，降低了细胞溶质氧化还原状态并增加了氧气消耗。所有这些快速作用都需要细胞外钙的存在，并且在鱼藤酮存在时消失，这表明EGF对糖异生的这种快速作用是线粒体呼吸刺激的继发效应。
