Plasma C5 Glucose–to–2H2O Ratio Does Not Provide an Accurate Assessment of Gluconeogenesis During Hyperinsulinemic-Euglycemic Clamps in Either Nondiabetic or Diabetic Humans

Abstract

OBJECTIVE-Measurement of plasma C2 glucose enrichment is cumbersome. Therefore, the plasma C5 glucose-to-2 H 2 O rather than the plasma C5-to-C2 glucose ratio commonly has been used to measure gluconeogenesis and glycogenolysis during hyperinsulinemic-euglycemic clamps. The validity of this approach is unknown. RESEARCH DESIGN AND METHODS-Ten nondiabetic and 10 diabetic subjects ingested2 H 2 O the evening before study. The following morning, insulin was infused at a rate of 0.6 mU ⅐ kg Ϫ1⅐ min Ϫ1 and glucose was clamped at ϳ5.3 mmol/l for 5 h. Plasma C5 glucose, C2 glucose, and 2 H 2 O enrichments were measured hourly from 2 h onward. RESULTS-Plasma C2 glucose and plasma2 H 2 O enrichment were equal in both groups before the clamp, resulting in equivalent estimates of gluconeogenesis and glycogenolysis. In contrast, plasma C2 glucose and plasma C5 glucose enrichments fell throughout the clamp, whereas plasma 2 H 2 O enrichment remained unchanged. Since the C5 glucose concentration and, hence, the C5 glucose-to-2 H 2 O ratio is influenced by both gluconeogenesis and glucose clearance, whereas the C5-to-C2 glucose ratio is only influenced by gluconeogenesis, the C5 glucose-to-2 H 2 O ratio overestimated (P Ͻ 0.01) gluconeogenesis during the clamp. This resulted in biologically implausible negative (i.e., calculated rates of gluconeogenesis exceeding total endogenous glucose production) rates of glycogenolysis in both the nondiabetic and diabetic subjects.CONCLUSIONS-Plasma C5 glucose-to-2 H 2 O ratio does not provide an accurate assessment of gluconeogenesis in nondiabetic or diabetic subjects during a traditional (i.e., 2-3 h) hyperinsulinemic-euglycemic clamp. The conclusions of studies that have used this approach need to be reevaluated. Diabetes 57:1800-1804, 2008 M easurement of gluconeogenesis in humans is difficult. The deuterated water method is widely used for this purpose (1-17). This method relies on the fact that the fifth carbon of glucose is labeled during gluconeogenesis, whereas the second carbon of glucose is labeled with deuterium during equilibration of glucose-6-phosphate and fructose-6-phoshate (1,2). Therefore, at steady state, the ratio of plasma glucose with deuterium on the fifth carbon (C5 glucose) to plasma glucose labeled on the second carbon (C2 glucose) equals the percentage of plasma glucose derived from gluconeogenesis (1,2). Measurement of C2 glucose enrichment is cumbersome. Since 2 H 2 O and C2 glucose enrichments are equal at steady state, many investigators have used the plasma C5 glucose-to-2 H 2 O ratio to calculate gluconeogenesis after an overnight fast (4 -7,9 -12,18). The C5 glucose-to-2 H 2 O ratio has also been used to measure gluconeogenesis during glucose clamps (4,6,7,11,12,18). However, the validity of this approach is uncertain. We have reported that the rate of gluconeogenesis measured during the final hour of a 3-h hyperinsulinemic-euglycemic clamp in lean nondiabetic subjects using the C5-to-C2 glucose ratio correlated with that measured in the same subjects us...

Time course of fractional gluconeogenesis after meat ingestion in healthy adults: a D2O study

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Dietary Proteins Contribute Little to Glucose Production, Even Under Optimal Gluconeogenic Conditions in Healthy Humans

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Effects of food-deprivation and refeeding on the regulation and sources of blood glucose appearance in European seabass (Dicentrarchus labrax L.)

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