Minassian C, Tarpin S, Mithieux G
INSERM 449, Faculté de Médecine R.T.H. Laënnec, Lyon, France.
Biochem Pharmacol. 1998 Apr 15;55(8):1213-9. doi: 10.1016/s0006-2952(97)00576-5.
We investigated the role of glucose-6 phosphatase (Glc6Pase), glucokinase (GK), and glucose-6 phosphate (Glc6P) in liver insulin resistance, an early characteristic of type 2 diabetes, and its correction by metformin. We determined hepatic glucose production (HGP) by tracer dilution, and enzyme activities and substrate concentrations after saline or insulin perfusions during euglycemic clamps in rats fed: 1) a standard hyperglucidic diet (S); 2) a high-fat diet (HF); and 3) a high-fat diet and treated with the oral antidiabetic metformin (HF/Met). Basal HGP was similar in the 3 groups: 75+/-8, 65+/-9.5 and 71+/-3 micromol x kg(-1) x min(-1) (means+/-SEM, N=5) in S, HF and HF/Met rats, respectively. Upon insulin perfusion at 240 pmol/hr, HGP was decreased by 35% in S rats (49+/-4.5 micromol x kg(-1) x min(-1), P < 0.01 vs. basal) and 65% in HF/Met rats (23+/-10 micromol x kg(-1) x min(-1), P < 0.01 vs basal), whereas it was not decreased in HF rats (60+/-12 micromol x kg(-1) x min(-1)), revealing insulin resistance. GK activity was lower (by 65%, P < 0.01) in HF and HF/Met rats (0.8+/-0.1 and 0.9+/-0.1 U/g liver, respectively) than in S rats (2.4+/-0.3 U/g). Microsomal Glc6Pase activity was lower (by 35%, P < 0.01) in HF and HF/Met rats (0.25+/-0.01 and 0.27+/-0.02 micromol r min(-1) x mg prot x (-1), respectively) than in S rats (0.39+/-0.03 micromol x min(-1) x mg prot x (-1)). Glc6P concentration was decreased by insulin perfusion at 480 pmol/hr in S and HF/Met rats (P < 0.05 vs. saline), but not in HF rats, in agreement with insulin resistance in the latter group. However, the differential inhibitions of HGP by insulin could not be ascribed to the variations in Glc6P concentrations. Metformin was present in the liver at a concentration of 27+/-2 nmol/g wet tissue and was not detected in the plasma. These results strongly suggest that the regulation of HGP by insulin additionally involves short-term regulatory mechanism(s) of Glc6Pase, occurring in vivo, and lost under in vitro conditions. These might be impaired in HF rats, in keeping with insulin resistance of HGP, and restored by metformin.
我们研究了葡萄糖-6磷酸酶（Glc6Pase）、葡萄糖激酶（GK）和葡萄糖-6磷酸（Glc6P）在肝脏胰岛素抵抗（2型糖尿病的早期特征）中的作用，以及二甲双胍对其的纠正作用。我们通过示踪剂稀释法测定肝脏葡萄糖生成（HGP），并在正常血糖钳夹期间，对喂食以下三种饲料的大鼠进行生理盐水或胰岛素灌注后，测定酶活性和底物浓度：1）标准高糖饮食（S）；2）高脂饮食（HF）；3）高脂饮食并口服抗糖尿病药物二甲双胍（HF/Met）。三组大鼠的基础HGP相似：S组、HF组和HF/Met组大鼠分别为75±8、65±9.5和71±3 μmol·kg⁻¹·min⁻¹（均值±标准误，N = 5）。在以240 pmol/hr的速度进行胰岛素灌注时，S组大鼠的HGP降低了35%（49±4.5 μmol·kg⁻¹·min⁻¹，与基础值相比P < 0.01），HF/Met组大鼠降低了65%（23±10 μmol·kg⁻¹·min⁻¹，与基础值相比P < 0.01），而HF组大鼠的HGP未降低（60±12 μmol·kg⁻¹·min⁻¹），显示出胰岛素抵抗。HF组和HF/Met组大鼠的GK活性（分别为0.8±0.1和0.9±0.1 U/g肝脏）低于S组大鼠（2.4±0.3 U/g）（降低了65%，P < 0.01）。微粒体Glc6Pase活性在HF组和HF/Met组大鼠中（分别为0.25±0.01和0.27±0.02 μmol·min⁻¹·mg蛋白⁻¹）低于S组大鼠（0.39±0.03 μmol·min⁻¹·mg蛋白⁻¹）（降低了35%，P < 0.01）。在以480 pmol/hr的速度进行胰岛素灌注时，S组和HF/Met组大鼠的Glc6P浓度降低（与生理盐水灌注相比P < 0.05），而HF组大鼠未降低，这与后一组的胰岛素抵抗一致。然而，胰岛素对HGP的不同抑制作用不能归因于Glc6P浓度的变化。肝脏中二甲双胍的浓度为27±2 nmol/g湿组织，血浆中未检测到。这些结果强烈表明，胰岛素对HGP的调节还涉及Glc6Pase的短期调节机制，该机制在体内发生，在体外条件下丧失。在HF组大鼠中这些机制可能受损，这与HGP的胰岛素抵抗一致，而二甲双胍可使其恢复。
