Landau B R, Wahren J, Chandramouli V, Schumann W C, Ekberg K, Kalhan S C
Department of Medicine, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106, USA.
J Clin Invest. 1996 Jul 15;98(2):378-85. doi: 10.1172/JCI118803.
Healthy subjects ingested 2H2O and after 14, 22, and 42 h of fasting the enrichments of deuterium in the hydrogens bound to carbons 2, 5, and 6 of blood glucose and in body water were determined. The hydrogens bound to the carbons were isolated in formaldehyde which was converted to hexamethylenetetramine for assay. Enrichment of the deuterium bound to carbon 5 of glucose to that in water or to carbon 2 directly equals the fraction of glucose formed by gluconeogenesis. The contribution of gluconeogenesis to glucose production was 47 +/- 49% after 14 h, 67 +/- 41% after 22 h, and 93 +/- 2% after 42 h of fasting. Glycerol's conversion to glucose is included in estimates using the enrichment at carbon 5, but not carbon 6. Equilibrations with water of the hydrogens bound to carbon 3 of pyruvate that become those bound to carbon 6 of glucose and of the hydrogen at carbon 2 of glucose produced via glycogenolysis are estimated from the enrichments to be approximately 80% complete. Thus, rates of gluconeogenesis can be determined without corrections required in other tracer methodologies. After an overnight fast gluconeogenesis accounts for approximately 50% and after 42 h of fasting for almost all of glucose production in healthy subjects.
健康受试者摄入重水，在禁食14小时、22小时和42小时后，测定血糖中与碳2、5和6结合的氢以及体内水中氘的富集情况。与碳结合的氢在甲醛中分离出来，甲醛再转化为六亚甲基四胺进行分析。葡萄糖中与碳5结合的氘相对于水中或直接相对于碳2的氘的富集程度等于糖异生形成的葡萄糖的比例。禁食14小时后，糖异生对葡萄糖生成的贡献为47±49%，禁食22小时后为67±41%，禁食42小时后为93±2%。使用碳5而非碳6的富集情况进行估算时，甘油向葡萄糖的转化包含在内。根据富集情况估计，丙酮酸中与碳3结合的氢（这些氢会变成与葡萄糖碳6结合的氢）以及通过糖原分解产生的葡萄糖中碳2的氢与水的平衡约完成80%。因此，无需像其他示踪方法那样进行校正就能确定糖异生的速率。在健康受试者中，禁食一夜后糖异生约占葡萄糖生成的50%，禁食42小时后几乎占所有葡萄糖生成。
