Pauliina Peltoniemi

Muscle blood flow and flow heterogeneity during exercise studied with positron emission tomography in humans

Abstract Blood flow is the main regulator of skeletal muscles oxygen supply, and several studies have shown heterogeneous blood flow among and within muscles. However, it remains unclear whether exercise changes the heterogeneity of flow in exercising human skeletal muscle. Muscle blood flow and spatial flow heterogeneity were measured simultaneously in exercising and in the contralateral resting quadriceps femoris (QF) muscle in eight healthy men using H152O and positron emission tomography. The relative dispersion (standard deviation/mean) of blood flow was calculated as an index of spatial flow heterogeneity. Average muscle blood flow in QF was 29 (10) ml · (kg muscle)−1 · min−1 at rest and 146 (54) ml · (kg muscle)−1 · min−1 during exercise (P=0.008 for the difference). Blood flow was significantly (P < 0.001) higher in the vastus medialis and the vastus intermedius than in the vastus lateralis and the rectus femoris, both in the resting and the exercising legs. Flow was more homogeneous in the exercising vastus medialis and more heterogeneous (P < 0.001) in the exercising vastus lateralis (P=0.01) than in the resting contralateral muscle. Flow was more homogeneous (P < 0.001) in those exercising muscles in which flow was highest (vastus intermedius and vastus medialis) as compared to muscles with the lowest flow (vastus lateralis and the rectus femoris). These data demonstrate that muscle blood flow varies among different muscles in humans both at rest and during exercise. Muscle perfusion is spatially heterogeneous at rest and during exercise, but responses to exercise are different depending on the muscle.

Human adipose tissue glucose uptake determined using [18F]-fluoro-deoxy-glucose ([18F]FDG) and PET in combination with microdialysis

Abstract.Aims/hypothesis: 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. Methods: [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 (rGUFDG) 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, rGUMD) was calculated by multiplying glucose extraction by regional blood flow. The LC was determined as the ratio of rGUFDG to rGUMD. Results: Rates of adipose tissue glucose uptake (rGUMD) 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 rGUMD and rGUFDG 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. Conclusion/interpretation: [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]