To determine the lumped constant (LC), which accounts for the differences in the transport and phosphorylation between [¹⁸F]-2-fluoro-2-deoxy-d-glucose ([¹⁸F]FDG) and glucose, for [¹⁸F]FDG in human adipose tissue.

[¹⁸F]FDG-PET was combined with microdialysis. Seven non-obese (29 ± 2 years of age, BMI 24 ± 1 kg/m²) and seven obese (age 32 ± 2 years of age, BMI 31 ± 1 kg/m²) men were studied during euglycaemic hyperinsulinaemia (1 mU/kg · min^–1 for 130 min). Abdominal adipose tissue [¹⁸F]FDG uptake (rGU_FDG) and femoral muscle glucose uptake were measured using [¹⁸F]FDG-PET. Adipose tissue perfusion was measured using [¹⁵O]-labelled water and PET, and interstitial glucose concentration using microdialysis. Glucose uptake (by microdialysis, rGU_MD) was calculated by multiplying glucose extraction by regional blood flow. The LC was determined as the ratio of rGU_FDG to rGU_MD.

Rates of adipose tissue glucose uptake (rGU_MD) were 36 % higher in the non-obese than in the obese patients (11.8 ± 1.7 vs 7.6 ± 0.8 μmol/kg · min^–1, p < 0.05, respectively) and a correlation between rGU_MD and rGU_FDG was found (r = 0.82, p < 0.01). The LC averaged 1.14 ± 0.11, being similar in the obese and the non-obese subjects (1.01 ± 0.15 vs 1.26 ± 0.15, respectively, NS). Muscle glucose uptake was fourfold to fivefold higher than adipose tissue glucose uptake in both groups.

[¹⁸F]FDG-PET seems a feasible tool to investigate adipose tissue glucose metabolism in human beings. Direct measurements with [¹⁸F]FDG-PET and microdialysis suggest a LC value of 1.14 for [¹⁸F]FDG in human adipose tissue during insulin stimulation and the LC does not appear to be altered in insulin resistance. Furthermore, the obese patients show insulin resistance in both adipose tissue and skeletal muscle. [Diabetologia (2001) 44: 2171–2179]