Lumped constant for [F-18] fluorodeoxyglucose in skeletal muscles of obeseand nonobese humans

Quantitative 2-[F-18]fluoro-2-deoxy-D-glucose ([F-18]FDG) positron emission tomography (PET) has been widely used to calculate glucose utilization in skeletal muscle. FDG-PET results depend partly on the lumped constant (LC), which accounts for the differences in the transport and phosphorylation be tween [F-18]FDG and glucose. In this study, we estimated the LC for [F-18]F DG directly in normal and in insulin-resistant obese subjects by combining FDG PET with the microdialysis technique. Eight obese [age 29.4 +/- 1.0 yr, body mass index (BMI) 33.6 +/- 1.0 kg/m(2)] and eight nonobese (age 25.0 /- 1.0 yr, BMI 23.1 +/- 1.0 kg/m(2)) males were studied during euglycemic h yperinsulinemia (1 mU.kg(-1).min(-1) for 150 min). Muscle blood flow was me asured using O-15-labeled water and PET. Muscle [F-18]FDG uptake (rGU(FDG)) was calculated with Patlak graphic analysis. Interstitial glucose concentr ation of the quadriceps femoris muscle was measured simultaneously with [F- 18]FDG scanning using microdialysis. Muscle glucose uptake (by microdialysi s, rGU(MD)) was calculated by multiplying glucose extraction by regional mu scle blood flow. A significant correlation was found between rGU(MD) and rG U(FDG) (r = 0.78, P < 0.01). The LC was determined as the ratio of the rGU( FDG) to the rGU(MD). The LC averaged 1.16 +/- 0.16 and was similar in the o bese and nonobese subjects (1.15 +/- 0.11 vs. 1.16 +/- 0.07, respectively, not significant). In conclusion, the microdialysis technique can be reliabl y combined with FDG PET to measure glucose uptake in skeletal muscle. Direc t measurements with these two independent techniques suggest an LC value of 1.2 for [F-18]FDG in human skeletal muscle during insulin stimulation, and the LC appears not to be sensitive to insulin resistance.