1 Turku Positron Emission Tomography Center and 2 Lundberg Laboratory for Diabetes Research, Department of Internal Medicine, University of Gothenburg, 41345 Gothenburg, Sweden; and 3 Department of Medicine, University of Turku, F-20520 Turku, Finland
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Quantitative
2-[18F]fluoro-2-deoxy-D-glucose
([18F]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
between [18F]FDG and glucose. In this study, we estimated
the LC for [18F]FDG 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/m2] and eight
nonobese (age 25.0 ± 1.0 yr, BMI 23.1 ± 1.0 kg/m2) males were studied during euglycemic
hyperinsulinemia (1 mU · kg1 · min
1 for 150 min). Muscle blood flow was measured using 15O-labeled
water and PET. Muscle [18F]FDG uptake
(rGUFDG) was calculated with Patlak graphic analysis. Interstitial glucose concentration of the quadriceps femoris muscle was
measured simultaneously with [18F]FDG scanning using
microdialysis. Muscle glucose uptake (by microdialysis,
rGUMD) was calculated by multiplying glucose extraction by
regional muscle blood flow. A significant correlation was found between
rGUMD and rGUFDG (r = 0.78, P < 0.01). The LC was determined as the ratio of the
rGUFDG to the rGUMD. The LC averaged 1.16 ± 0.16 and was similar in the obese and nonobese subjects (1.15 ± 0.11 vs. 1.16 ± 0.07, respectively, not significant). In
conclusion, the microdialysis technique can be reliably combined with
FDG PET to measure glucose uptake in skeletal muscle. Direct
measurements with these two independent techniques suggest an LC value
of 1.2 for [18F]FDG in human skeletal muscle during
insulin stimulation, and the LC appears not to be sensitive to insulin resistance.
glucose transport; glucose phosphorylation; insulin resistance; microdialysis; positron emission tomography
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
SKELETAL MUSCLE IS QUANTITATIVELY the most important glucose-utilizing tissue, accounting for 70-80% of glucose utilized during hyperinsulinemia (11). Use of positron emission tomography (PET) and 2-[18F]fluoro-2-deoxy-D-glucose ([18F]FDG) as a glucose tracer enables noninvasive regional measurements of muscle glucose uptake in vivo in humans. This method has been widely used to study healthy subjects (36) and, recently, also insulin-resistant subjects (23, 27, 28, 37, 48, 54).
The tracer [18F]FDG is a labeled glucose analog in which the natural D-glucose's other hydrogen in the 2-position is replaced by fluorine-18. It is an ideal positron-emitting radionuclide, having low positron energy (0.64 MeV) and a half-life of 109.8 min, which allows kinetic studies (56). [18F]FDG is transported into the muscle cell by the same carriers as glucose, and inside the cell, it is phosphorylated to [18F]FDG-6-phosphate by hexokinase II. However, affinities of deoxyglucose for transport and phosphorylation differ from those of glucose, because glucose transporters favor deoxyglucose over glucose, whereas the affinity of hexokinase is higher for glucose than for deoxyglucose (6, 20). Therefore, a correction factor called the lumped constant (LC) has been experimentally derived and used to correct for differences in transport and phosphorylation between FDG and glucose. After phosphorylation, [18F]FDG-6-phosphate can be incorporated into glycogen (55), but it cannot enter glycolysis (18). Consequently, [18F]FDG-6-phosphate is irreversibly trapped in the muscle cell.
The microdialysis technique has been successfully employed to directly measure regional metabolic balance in human subcutaneous and muscle tissue (21). The technique has been previously validated to estimate interstitial glucose concentration (16, 30). Microdialysis samples the interstitial fluid and, provided that in situ calibration is performed, enables the estimation of glucose concentration in the interstitial fluid (29). The extraction of glucose can be calculated, and, if the regional tissue blood flow is quantitated, the glucose uptake can be estimated by use of Fick's equation (21). Thus PET techniques and microdialysis both open unique possibilities for measurement of local metabolic balance rates. Moreover, the combination of techniques seems ideal, because PET provides more accurate blood flow measurements than plethysmography (38), which is more commonly used with microdialysis. Use of PET and radiowater allows direct and regional assessment of skeletal muscle blood flow without interference from other leg tissues and without invasive catheterizations.
In skeletal muscle studies, an LC of 1.0 has been commonly used (31, 36) despite the differences in the transport and phosphorylation of FDG relative to that of glucose (6, 20). Recently, Kelley et al. (24) determined the LC for [18F]FDG in human skeletal muscle using FDG PET, [3H]glucose, and venous occlusion strain-gauge plethysmography. Their data suggested an LC value of 1.2 in healthy lean volunteers, and insulin did not seem to influence the LC. However, we have previously shown that whole leg perfusion is not identical to skeletal muscle perfusion (24); furthermore, in the study of Kelley et al., only normal subjects, not insulin-resistant subjects, were included. In a number of previous studies, a close relationship was demonstrated between whole body glucose uptake measured with the euglycemic clamp technique and femoral muscle glucose uptake measured with FDG PET (34, 36, 37). When an LC of 1.0 was used, FDG PET-derived glucose uptake was similar, as measured with the forearm balance technique, and was 79% of the whole body glucose uptake (36) measured with the insulin glucose clamp technique. However, in insulin-resistant states such as obesity, where impaired cellular glucose uptake is the major cause of insulin resistance (5, 26) and changes in rates of glucose transport have been demonstrated (13), the LC might be altered.
PET combined with the microdialysis technique enables direct, relatively noninvasive measurement of the LC in vivo in human skeletal muscle. In the present study, we used these techniques to estimate the LC for [18F]FDG in healthy humans. We also tested whether the LC is altered in insulin-resistant obese subjects.
![]() |
RESEARCH DESIGN AND METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Subjects.
Eight nonobese [age 25 ± 1 yr, body mass index (BMI) 23.1 ± 1.0 kg/m2] and eight obese (age 29 ± 1 yr, BMI
33.6 ± 1.0 kg/m2) males were studied. The
characteristics of the study subjects are shown in Table
1. The subjects were healthy, as judged
by history, physical examination, and routine laboratory tests, and they were not taking any medications. The nature, purpose, and potential risks of the study were explained to all subjects before they
gave their written informed consent to participate. The study was
approved by the Joint Commission of the Ethics Committee of the
University of Turku and Turku University Central Hospital.
|
Study design.
The design of this study is shown in Fig.
1. Studies were performed after an
overnight fast. Alcohol and caffeine were prohibited 24 h before
the study, and the subjects were instructed to avoid strenuous physical
activity 1 day before the study. The subjects were supine during the
study. Two catheters were inserted, one in an antecubital vein of the
left hand for the infusion of glucose and insulin and for injections of
[15O]H2O and [18F]FDG and one
in the radial artery for blood sampling. The microdialysis catheter was
inserted into the left vastus medialis muscle. The study for each
subject consisted of a 150-min normoglycemic hyperinsulinemic (1 mU · kg1 · min
1) period.
During hyperinsulinemia, normoglycemia was maintained using a variable
rate of infusion of 20% glucose (12). The steady state
for serum insulin and arterial plasma glucose concentrations was kept
during the clamp for 150 min. During the period of FDG scanning,
between 60 and 150 min, the coefficient of variation (CV) for arterial
glucose concentrations was 3.2 ± 0.8% without any trend and was
similar between the study groups.
|
Microdialysis.
The microdialysis procedure was performed as previously described
(29, 33). The microdialysis catheter (dialysis membrane 16 × 0.5 mm, 20 kDa mol mass cut-off; CMA Microdialysis,
Stockholm, Sweden) was inserted into the left vastus medialis muscle 10 cm above the knee joint (Fig. 2), without
any local anesthesia, by vertical puncture of the surface of
disinfected skin with a 20-gauge intravenous plastic cannula, which was
then inserted into the muscle. The steel mandrin was removed, and the
microdialysis catheter was inserted subsequently, after which the
plastic cannula was also removed, leaving the catheter in the muscle.
The inlet of the microdialysis catheter was connected to a
microinjection pump (CMA/100, CMA Microdialysis), which perfused the
catheter at a flow rate of 2.5 µl/min. Isotonic saline with an
addition of 2.0 mmol/l glucose was used as the perfusion fluid. After
60 min of equilibration, the first four dialysates were collected at
5-min intervals and thereafter at 10-min intervals until the end of the
study. After calibration of the microdialysis catheter, interstitial glucose concentrations were determined. The CV for interstitial glucose
concentrations was 9.5 ± 1.5% between 60 and 150 min and was
similar between the study groups.
|
Calibration procedure. The internal reference technique was applied to assess the in vivo probe recovery in each probe (30). For internal reference calibration, 5 µCi/ml of [3H]glucose (Amersham) were added to the perfusates, and the percentage of loss over the membrane was taken as an estimate of recovery (32). The mean in vivo recovery for glucose was 20 ± 0.1%.
Production of PET tracers. For production of 15O (t1/2 = 123 s), a low-energy deuteron accelerator, Cyclone 3, was used (Ion Beam Application, Louvain-la-Neuve, Belgium). [15O]H2O was produced by means of a dialysis technique in a continuously working water module (10). Sterility and pyrogenity tests were performed daily to verify the purity of the product. [18F]FDG (t1/2 = 109 min) was synthesized with an automatic apparatus as described by Hamacher et al. (15). The specific radioactivity at the end of the synthesis was 76 GBq/µmol, and the radiochemical purity exceeded 98%.
Image acquisition and processing. An eight-ring ECAT 931/08-tomograph (Siemens/CTI, Knoxville, TN) was used for image acquisition. The scanner has an axial resolution of 6.7 mm and an in-plane resolution of 6.5 mm (50). The subject was positioned in the tomograph with the femoral region within the gantry. Before the emission scannings, a transmission scan for correction of photon attenuation was performed for 20 min with a removable ring source containing 68Ge. All data were corrected for dead time, decay, and measured photon attenuation. For image processing, a recently developed Bayesian iterative reconstruction algorithm using median root prior with 150 iterations and the Bayesian coefficient of 0.3 was applied (1).
Regions of interest. Regions of interest (ROIs) were drawn in the anteromedial muscle compartments of both femoral regions in four cross-sectional slices, carefully avoiding large blood vessels (44). Localization of the muscle compartments was verified by comparing the flow images with the transmission image, which provides a topographical distribution of tissue density. The ROIs outlined in the flow images were copied to the [18F]FDG images to obtain quantitative data from identical regions.
Measurement of muscle blood flow. For measurement of blood flow, 1.1-1.5 GBq [15O]H2O was injected intravenously, and dynamic scanning was performed for 6 min (6 × 5-s, 6 × 15-s, and 8 × 30-s frames). To determine the input function, blood from the radial artery was continuously withdrawn using a pump at a speed of 6 ml/min. The radioactivity concentration was measured with a two-channel detector system (Scanditronix, Uppsala, Sweden) calibrated to the well counter (Wizard 1480; Wallac, Turku, Finland) and the PET scanner, as previously described (46). The arterial input curve was corrected for dispersion and delay as previously described (38). The autoradiographic method and a 250-s integration time were applied to calculate blood flow pixel by pixel. This method has been previously validated against the steady-state method (46) and blood flow measured with strain-gauge plethysmography (38).
Measurement of muscle glucose uptake with [18F]FDG (rGUFDG). For measurement of [18F]FDG uptake, 0.18-0.25 GBq of [18F]FDG was injected intravenously over 2 min, and a dynamic scan for 90 min was started (1 × 60-s, 6 × 30-s, 1 × 60-s, 3 × 300-s, and 7 × 600-s frames). Arterial blood samples for measurement of plasma radioactivity were withdrawn as previously described (36).
The three-compartment model of [18F]FDG kinetics was used as described previously (19, 35, 36, 47). Plasma and tissue time-activity curves for the anteromedial muscle compartments were analyzed graphically to quantitate the fractional rate of tracer uptake (Ki) (41). The time-activity points 10-90 min after the [18F]FDG injection were used to determine the slope by linear regression. The rGUFDG was calculated by multiplying Ki by the plasma glucose concentration ([Glc]p).Measurement of rGUMD with microdialysis.
After calibration, interstitial fluid glucose concentration was
measured using microdialysis. Glucose uptake was calculated on the
basis of Fick's equation by multiplying glucose extraction fraction
with blood flow (21). Blood flow was measured using [15O]H2O and PET in the same muscle
compartment where the interstitial glucose concentration was measured,
i.e., in the vicinity of the microdialysis probe. The muscle volume in
which blood flow was measured was ~15 cm3. The extraction
fraction for glucose was calculated as previously described (16,
21) using the glucose permeability surface area product (PS)~4
ml · min1 · 100 g
1
(7, 39, 52, 53) and the measured arterial (A) and
interstitial (I) concentrations. Thereafter, the rGUMD was
calculated by multiplying glucose extraction by blood flow (BF)
![]() |
Calculation of LC.
The LC was calculated by dividing rGUFDG measured using PET
by the rGUMD measured using microdialysis
![]() |
Whole body glucose uptake. Whole body glucose uptake was determined independently of the PET measurements by use of the euglycemic hyperinsulinemic clamp technique as previously described (12). During hyperinsulinemia, normoglycemia was maintained by use of a variable rate of infusion of 20% glucose based on arterial plasma glucose measurements (22). The rate of whole body glucose uptake was calculated from the same time period that the measurements of muscle blood flow and glucose uptake were performed.
Other measurements. Arterial and plasma glucose were determined in duplicate by the glucose oxidase method (Analox GM7 Analyzer, Analox Instruments, London, UK). Serum insulin concentrations were measured basally and at 30-min intervals during the insulin infusion using a double-antibody radioimmunoassay (Pharmacia Insulin RIA kit, Pharmacia). Body fat content was estimated from four skinfolds (subscapular, triceps brachii, biceps brachii, and crista iliaca), as measured with calipers.
Statistical methods. All results are expressed as means ± SE. The differences between the two groups were compared using Student's unpaired t-test or the Wilcoxon matched pairs test, where appropriate. Correlations were calculated using Pearson's correlation analysis. The statistical calculations were performed with the Statistica (StatSoft, Tulsa, OK) statistical program. Significance was set at the P < 0.05 level.
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Metabolic characteristics during the studies. Characteristics of the study subjects are shown in Table 1. During hyperinsulinemia, plasma glucose concentrations were similar [5.3 ± 0.03 vs. 5.3 ± 0.02 mmol/l, obese vs. nonobese subjects, respectively, not significant (NS)], but serum insulin concentrations were slightly higher in the obese than in the nonobese subjects (67 ± 5.0 vs. 49 ± 4.0 mU/l, respectively, P < 0.05).
Whole body glucose uptake.
Insulin-stimulated whole body glucose uptake expressed per body weight
was 123% higher in the nonobese than in the obese subjects (32.3 ± 2.6 vs. 13.4 ± 1.0 µmol · kg body
wt1 · min
1, nonobese vs. obese,
P < 0.001; Fig. 3). When
expressed per lean body mass (LBM), insulin-stimulated whole body
glucose uptake was 70% higher in the nonobese than in the obese
subjects (38.9 ± 3.3 vs. 23.4 ± 2.0 µmol · kg
body wt
1 · min
1, respectively,
P < 0.001).
|
Muscle blood flow.
Rates of insulin-stimulated muscle blood flow were slightly higher in
the nonobese than in the obese subjects, but this difference was
statistically nonsignificant (4.2 ± 1.1 vs. 1.9 ± 0.3 ml · 100 g1 · min
1,
P = 0.07; Table 2).
|
Muscle glucose uptake measured using [18F]FDG and
PET.
During insulin stimulation, fractional [18F]FDG uptake
values (Ki) were higher in femoral muscles of
the nonobese than in the obese subjects (0.009 ± 0.002 vs.
0.004 ± 0.003 min1, respectively,
P < 0.01; Table 2 and Fig.
4). Consequently, muscle glucose uptake
values measured with [18F]FDG (rGUFDG) and
calculated by multiplying Ki by the plasma glucose concentration were significantly higher in the nonobese than in the obese subjects (46.3 ± 8.2 vs. 18.8 ± 1.4 µmol · kg muscle
1 · min
1,
respectively, P < 0.001; Table 2). Muscle glucose
uptake values measured with [18F]FDG correlated with
rates of insulin-stimulated muscle blood flow in the pooled data
(r = 0.60, P < 0.05; data not shown). Muscle glucose uptake values measured using [18F]FDG
correlated with whole body glucose uptake values expressed per LBM in
the pooled data (r = 0.84, P < 0.01;
Fig. 5).
|
|
Muscle glucose uptake measured by microdialysis.
Insulin-stimulated femoral muscle rGUMD was significantly
higher in the nonobese than in the obese subjects (41.4 ± 5.9 vs. 17.0 ± 1.6 µmol · kg
muscle1 · min
1, nonobese vs. obese,
P < 0.005; Table 2 and Fig. 3). During hyperinsulinemia, interstitial glucose concentrations were higher in
the obese (4.13 ± 0.17 mmol/l) than in the nonobese subjects (3.39 ± 0.16 mmol/l, P < 0.01; Table 2). There
was an inverse correlation between interstitial glucose concentration
and muscle glucose uptake values measured with [18F]FDG
in the pooled data (r =
0.50, P < 0.05). Femoral muscle glucose uptake correlated with whole body glucose
uptake expressed per LBM in the pooled data (r = 0.75, P < 0.01; Fig. 5).
Lumped constant.
The LC, calculated by dividing rGUFDG by rGUMD,
averaged 1.16 ± 0.07 for the entire group, 1.16 ± 0.16 for
the nonobese, and 1.15 ± 0.11 and for the obese subjects
(P = NS; Table 2). Regional PET-derived glucose uptake
(rGUPET) correlated with rGUMD
(r = 0.78, P < 0.01; Fig.
6). No association was found between the LC and whole body glucose uptake (P = 0.15, r = 0.43) or between the LC and serum insulin
concentrations (P = 0.76, r = 0.14) in the pooled data or when the groups were analyzed separately (data not
shown).
|
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The present study was undertaken to estimate directly the LC for [18F]FDG in human skeletal muscle during insulin stimulation. Furthermore, we tested whether insulin resistance alters the LC. We found that the LC for [18F]FDG averaged 1.2 and was unaltered in insulin-resistant obese subjects. No correlation was found between the LC and serum insulin concentrations (range 37-85 mU/l) during the insulin clamp.
The model for quantitation rates of glucose utilization using labeled 2-deoxyglucose as a tracer was first introduced by Sokoloff et al. (49) to quantitate rates of cerebral glucose utilization in rats. This model has been subsequently applied in PET studies and used to quantitate glucose uptake rates with [18F]FDG in skeletal muscle in humans (27, 28, 36, 43, 54). This model is applicable only in homogenous tissues under steady-state conditions when [18F]FDG and [18F]FDG-6-phosphate are present in tracer amounts (42). In addition, the model assumes that dephosphorylation of [18F]FDG-6-phosphate is nonsignificant (41). The Ki can be calculated by use of graphic analysis of plasma and tissue time-activity curves (41). Thereafter, the rate of glucose uptake can be calculated by multiplying Ki by the [GLC]p divided by an LC, which accounts for differences in the transport and phosphorylation of [18F]FDG and glucose. In the present study, the steady-state conditions required by the model were attained by the insulin clamp technique, [18F]FDG was used in tracer amounts, and the graphic analysis of the plasma and tissue time-activity curves showed linear slopes (Fig. 4), supporting the assumption that [18F]FDG was irreversibly trapped within the muscle cells and not dephosphorylated.
From experimental animal studies, the LC for [18F]FDG in skeletal muscles has been estimated to be 1.0 (31), and this value has previously been commonly used in human skeletal muscle studies. Recently, Kelley et al. (24) determined the LC for [18F]FDG in human skeletal muscle using FDG PET, [3H]glucose, and venous occlusion strain-gauge plethysmography. Their data suggested an LC value of 1.2 in healthy lean volunteers, and insulin did not seem to influence the LC. However, we have previously shown that whole leg perfusion is not identical with skeletal muscle perfusion (45); furthermore, in the study of Kelley et al., only normal subjects, not insulin-resistant subjects, were included. Skeletal muscle LC for other 2-deoxyglucoses, i.e., for 2-deoxy[1-3H]glucose and 2-deoxy[1-14C]glucose, has been previously estimated in rats and found to range from 0.75 to 1.20 (4, 14). However, those results cannot be used directly for human skeletal muscle or for [18F]FDG, which is structurally more similar to glucose than either 2-deoxy[1-3H]glucose or 2-deoxy[1-14C]glucose. In the present study, by combining the microdialysis technique with PET, the LC for [18F]FDG was estimated directly in human skeletal muscle and averaged 1.2 in both the nonobese and the obese subjects during insulin stimulation. This finding is consistent with our previous studies (34, 36) and with the study of Kelley et al., suggesting that LC is close to unity.
Microdialysis has not previously been combined with the FDG-PET technique; it has been used mainly in the assessment of interstitial glucose concentration in human subcutaneous and muscle tissue. The interstitial glucose concentrations measured in the present study are comparable with those found in previous studies (16, 30, 32). All microdialysis catheters used in the present study were calibrated in steady-state conditions using the internal reference technique, which has been previously shown to give similar recovery coefficients to the equilibration technique in humans (16). After the calibrated assessment of interstitial glucose concentration, the glucose uptake was calculated using Fick's principle by multiplying the glucose extraction fraction with blood flow. The direct validation to measure glucose uptake using microdialysis against arteriovenous methods during insulin stimulation is lacking. The recent study of Stallknecht et al. (51) was designed to evaluate the reliability of the microdialysis technique for the assessment of glucose uptake in adipose tissue. They found that calculated and measured venous plasma glucose concentrations were identical in adipose tissue, but that glucose uptake rates calculated from microdialysis and 133Xe washout measurements and by Fick's principle only tended toward correlation. However, any small errors in absolute values of fasting plasma glucose calculated from microdialysis had significant influence on the calculated arteriovenous differences. Furthermore, when arteriovenous difference was multiplied by an inaccurate blood flow estimated from 133Xe washout, their finding of nonsignificant association between glucose uptake rates was not considered to be surprising (51). Challenging their results, we found a significant correlation between glucose uptake measured with microdialysis and FDG PET (r = 0.78, P < 0.01). Our study design differed from the study of Stallknecht et al. in that the present study was performed after an overnight fast during steady-state hyperinsulinemia leading to higher arteriovenous glucose differences. Furthermore, skeletal muscle perfusion was measured directly with radiowater in the vicinity of the microdialysis probe, in the same region of interest where the glucose and [18F]FDG uptake were measured. Use of PET and radiowater allows direct and regional assessment of skeletal muscle blood flow and metabolism without interference from other leg tissues and without invasive catheterizations. Regional glucose and [18F]FDG uptake were calculated in the same region with two different and independent methods, and from these measurements the LC was estimated. Thus, in the present study, the finding that muscle glucose uptake assessed by PET correlated closely with the uptake rates estimated by microdialysis suggests that these two methods can be reliably combined.
In the calculation of glucose uptake measured with microdialysis, the
value of permeability surface area product (PS) is needed. Only
preliminary data of the PS value for glucose in human skeletal muscle
during physiological insulin stimulation are available, and its
influence on the results must be carefully taken into account.
Trap-Jensen and Lassen (52) determined the PS for fructose and found it to be 5.5 ml · min1 · 100 g
1 in human forearm during exercise. Crone
(8) reported the PS value for D-glucose to be
4.6 ml · min
1 · 100 g
1 in
cat gastrocnemius muscle. For larger molecules such as
51Cr-EDTA and sucrose, PS values between 3.0 and 5.5 ml · min
1 · 100 g
1 in
skeletal muscle have been reported (7, 39, 52, 53). These
previously reported PS values for hexose molecule are in accordance
with the applied PS value of 4 ml · min
1 · 100 g
1 (Fig.
7). Moreover, when it is taken into
account that glucose is a smaller molecule than sucrose and
51Cr-EDTA and that the permeability has been demonstrated
to be 60% higher for hexose than for sucrose in human forearm
(53), there is strong evidence that an applied PS value of
4 ml · min
1 · 100 g
1 is
adequate within the range of blood flow rates presently registered (9, 39, 40). This is also in agreement with the data from direct measurements of PS for glucose in the human forearm during insulin stimulation, which suggested that PS for glucose averaged 4 ml · min
1 · 100 g
1 and was
not dependent on plasma insulin concentration (S. Gudbjornsdottir, J. Wahren, and P. Lönnroth, personal
communication).
|
The effect of the PS value on the LC is illustrated by the following
example. If mean blood flow is 3.1 ml · 100 g1 · min
1 (Table 2), and the PS
value varies from 3 to 5 ml · min
1 · 100 g
1, the LC varies from 1.39 to 1.08 (Fig. 7). Hence, PS
values >3 ml · min
1 · 100 g
1 have only a minor effect on the value of the LC.
However, it should be noted that blood flow has been found to correlate
with PS value, but the PS-to-blood flow ratio has been shown to be constant at such low blood flow rates as presented in this study (9). Thus the nonsignificant difference in blood flow
rates between the groups in the present study was not influencing the LC value, which was found to be similar in the obese and nonobese subjects. Also, the recent data by Kelley et al. (24) give
indirect support for the applied PS value; namely, if the PS is
calculated on the basis of their data, using a value of 1.2 for LC, the
PS value will be ~4 ml · min
1 · 100 g
1.
In the present study, blood flow and glucose uptake rates correlated, and, in accord with previous observations in obese subjects (25), the obese subjects of this study tended to have a lower blood flow rate. It has been suggested that the lower blood flow rate demonstrated in insulin-resistant muscle per se could mediate the insulin resistance by means of failure to deliver hormones and/or nutrients to the cells (2, 25). However, some other studies have shown that the impact of variations in blood flow in normal (32) and insulin-resistant muscle is minor or absent (16). The present study further underlines this conclusion, because obese subjects had a higher muscle interstitial glucose concentration compared with lean subjects. Thus, despite lower blood flow rates, insulin-resistant muscles have higher interstitial glucose levels due to a low elimination rate of glucose (16). Recently, it has been demonstrated that induction of insulin resistance in muscle reduces blood flow rate (17). Thus one could speculate that the attenuated action of insulin on glucose metabolism might be a causal factor behind the reduced blood flow of insulin-resistant muscle.
Glucose transporters favor [18F]FDG over glucose, whereas the affinity of hexokinase for glucose is higher than that for 2-deoxyglucose (6); thus one could hypothesize that the LC might be altered in states such as obesity, where rates of either glucose transport or phosphorylation are changed. Obesity is a major cause of insulin resistance in humans (3), and it is characterized by an inability of insulin to normally increase glucose uptake in skeletal muscles. Previous in vivo studies have demonstrated impaired cellular glucose uptake to be the major cause of insulin resistance in obesity (5, 26). Furthermore, in a study of intact muscle strips, decreased rates of glucose transport have been found in muscles of morbidly obese subjects (13). Yet, in the present study, we found that the LC was unchanged in the insulin-resistant obese subjects, who (consistent with previous data) exhibited a 55% reduction in whole body and a 59% reduction in femoral muscle glucose uptakes compared with the nonobese subjects. Interstitial glucose concentrations measured with the microdialysis technique were higher in the obese than in the nonobese subjects. From the present data, we are unable to conclude whether glucose transport or hexokinase activity is altered in the obese subjects, but the present finding of higher interstitial glucose concentration of the obese subjects seems to support the hypothesis that glucose transport is decreased in obesity. This is in accord with a previous study by Kelley et al. (23), which demonstrated a reduction in the insulin response of the transport rate constant in obese nondiabetic subjects.
In summary, it is feasible to combine the microdialysis technique with PET for the assessment of glucose uptake in skeletal muscle in vivo. By use of these two independent methods, direct measurements of the LC in human skeletal muscle demonstrate the LC value of 1.2 for [18F]FDG. Furthermore, the LC appears not to be sensitive to insulin resistance.
![]() |
ACKNOWLEDGEMENTS |
---|
We thank all the personnel in the Turku PET Centre for skillful technical assistance.
![]() |
FOOTNOTES |
---|
This work was supported by grants from the Research Foundation of the Orion Corporation (P. Peltoniemi), the Novo Nordisk Foundation (P. Nuutila), the Academy of Finland (P. Nuutila), the Turku University Foundation (P. Peltoniemi), and by the Yrjö Jahnsson Foundation (P. Peltoniemi), the Swedish Researcher Council (Project 10864), the Swedish Diabetes Association, and Novo Pharma.
Address for reprint requests and other correspondence: P. Peltoniemi, Turku PET Center, Univ. of Turku, PO Box 52, 20520 Turku, Finland (E-mail: papelto{at}utu.fi).
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Received 24 March 2000; accepted in final form 6 July 2000.
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
1.
Alenius, S,
and
Ruotsalainen U.
Bayesian image reconstruction for emission tomography based on median root prior.
Eur J Nucl Med
24:
258-265,
1997[ISI][Medline].
2.
Baron, AD,
Laakso M,
Brechtel G,
Hoit B,
Watt C,
and
Edelman SV.
Reduced postprandial skeletal muscle blood flow contributes to glucose intolerance in human obesity.
J Clin Endocrinol Metab
70:
1525-1533,
1990[Abstract].
3.
Björntorp, P.
Obesity.
Lancet
350:
423-426,
1997[ISI][Medline].
4.
Burnol, AF,
Ferre P,
Leturque A,
and
Girard J.
Effect of insulin on in vivo glucose utilization in individual tissues of anesthetized lactating rats.
Am J Physiol Endocrinol Metab
252:
E183-E188,
1987
5.
Castillo, C,
Bogardus C,
Bergman R,
Thuillez P,
and
Lillioja S.
Interstitial insulin concentrations determine glucose uptake rates but not insulin resistance in lean and obese men.
J Clin Invest
93:
10-16,
1994[ISI][Medline].
6.
Crane, PD,
Pardridge WM,
Braun LD,
and
Oldendorf WH.
Kinetics of transport and phosphorylation of 2-fluoro-2-deoxy-D-glucose in rat brain.
J Neurochem
40:
160-167,
1983[ISI][Medline].
7.
Crone, C.
The permeability of capillaries in various organs as determined by use of the "indicator diffusion" method.
Acta Physiol Scand
58:
292-305,
1963[ISI].
8.
Crone, C.
Transcapillary transport of D- and L-glucose in isolated skeletal muscle.
Acta Physiol Scand
87:
138-144,
1973[ISI][Medline].
9.
Crone, C,
and
Levitt DG.
Capillary permeability to small solutes.
In: The Cardiovascular System. Microcirculation. Bethesda, MD: Am. Physiol. Soc, 1984, sect. 2, Vol. IV, pt. 1, chapt. 10, p. 411-466.
10.
Crouzel, C,
Clarc J,
Brihaye C,
Långström B,
Lemaire C,
Meyer G,
Nebeling B,
and
Stone-Nelander S.
Radiochemistry automation for PET.
In: Radiopharmaceuticals for Positron Emission Tomography, edited by Stöcklin G,
and Pike V. Dordrecht, The Netherlands: Kluwer Academic, 1993, p. 45-90.
11.
DeFronzo, RA,
Ferrannini E,
Sato Y,
Felig P,
and
Wahren J.
Synergistic interaction between exercise and insulin on peripheral glucose uptake.
J Clin Invest
68:
1468-1474,
1981[ISI][Medline].
12.
DeFronzo, RA,
Tobin JD,
and
Andres R.
Glucose clamp technique: a method for quantifying insulin secretion and resistance.
Am J Physiol Endocrinol Metab Gastrointest Physiol
237:
E214-E223,
1979
13.
Dohm, GL,
Tapscott EB,
Pories WJ,
Dabbs DJ,
Flickinger EG,
Meelheim D,
Fushiki T,
Atkinson SM,
Elton CW,
and
Caro JF.
An in vitro human muscle preparation suitable for metabolic studies. Decreased insulin stimulation of glucose transport in muscle from morbidly obese and diabetic subjects.
J Clin Invest
82:
486-494,
1988[ISI][Medline].
14.
Ferre, P,
Leturque A,
Burnol AF,
Penicaud L,
and
Girard J.
A method to quantify glucose utilization in vivo in skeletal muscle and white adipose tissue of the anaesthetized rat.
Biochem J
228:
103-110,
1985[ISI][Medline].
15.
Hamacher, K,
Coenen HH,
and
Stocklin G.
Efficient stereospecific synthesis of no-carrier-added 2-[18F]-fluoro-2-deoxy-D-glucose using aminopolyether-supported nucleophilic substitution.
J Nucl Med
27:
235-238,
1986[Abstract].
16.
Holmäng, A,
Müller M,
Andersson OK,
and
Lönnroth P.
Minimal influence of blood flow on interstitial glucose and lactate-normal and insulin-resistant muscle.
Am J Physiol Endocrinol Metab
274:
E446-E452,
1998
17.
Holmäng, A,
Nilsson C,
Niklasson M,
Larsson BM,
and
Lönnroth P.
Induction of insulin resistance by glucosamine reduces blood flow but not interstitial levels of either glucose or insulin.
Diabetes
48:
106-111,
1999[Abstract].
18.
Horton, RW,
Meldrum BS,
and
Bachelard HS.
Enzymic and cerebral metabolic effects of 2-deoxy-D-glucose.
J Neurochem
21:
507-520,
1973[ISI][Medline].
19.
Huang, SC,
Phelps ME,
Hoffman EJ,
Sideris K,
Selin CJ,
and
Kuhl DE.
Noninvasive determination of local cerebral metabolic rate of glucose in man.
Am J Physiol Endocrinol Metab
238:
E69-E82,
1980
20.
Jacobs, AE,
Oosterhof A,
and
Veerkamp JH.
2-Deoxy-D-glucose uptake in cultured human muscle cells.
Biochim Biophys Acta
1051:
230-236,
1990[ISI][Medline].
21.
Jansson, PA,
Larsson A,
Smith U,
and
Lönnroth P.
Glycerol production in subcutaneous adipose tissue in lean and obese humans.
J Clin Invest
89:
1610-1617,
1992[ISI][Medline].
22.
Kadish, AH,
and
Hall DA.
A new method for the continuous monitoring of blood glucose by measurement of dissolved oxygen.
Clin Chem
11:
869-875,
1965[ISI][Medline].
23.
Kelley, DE,
Mintun MA,
Watkins SC,
Simoneau JA,
Jadali F,
Fredrickson A,
Beattie J,
and
Theriault R.
The effect of non-insulin-dependent diabetes mellitus and obesity on glucose transport and phosphorylation in skeletal muscle.
J Clin Invest
97:
2705-2713,
1996
24.
Kelley, DE,
Williams KV,
Price JC,
and
Goodpaster B.
Determination of the lumped constant for [18F]fluorodeoxyglucose in human skeletal muscle.
J Nucl Med
40:
1798-1804,
1999[Abstract].
25.
Laakso, M,
Edelman SV,
Brechtel G,
and
Baron AD.
Decreased effect of insulin to stimulate skeletal muscle blood flow in obese man. A novel mechanism for insulin resistance.
J Clin Invest
85:
1844-1852,
1990[ISI][Medline].
26.
Laakso, M,
Edelman SV,
Olefsky JM,
Brechtel G,
Wallace P,
and
Baron AD.
Kinetics of in vivo muscle insulin-mediated glucose uptake in human obesity.
Diabetes
39:
965-974,
1990[Abstract].
27.
Laine, H,
Knuuti MJ,
Ruotsalainen U,
Utriainen T,
Oikonen V,
Raitakari M,
Luotolahti M,
Kirvelä O,
Vicini P,
Cobelli C,
Nuutila P,
and
Yki-Järvinen H.
Preserved relative dispersion but blunted stimulation of mean flow, absolute dispersion, and blood volume by insulin in skeletal muscle of patients with essential hypertension.
Circulation
97:
2146-2153,
1998
28.
Laine, H,
Yki-Järvinen H,
Kirvelä O,
Tolvanen T,
Raitakari M,
Solin O,
Haaparanta M,
Knuuti J,
and
Nuutila P.
Insulin resistance of glucose uptake in skeletal muscle cannot be ameliorated by enhancing endothelium-dependent blood flow in obesity.
J Clin Invest
101:
1156-1162,
1998
29.
Lönnroth, P,
Jansson PA,
and
Smith U.
A microdialysis method allowing characterization of intercellular water space in humans.
Am J Physiol Endocrinol Metab
253:
E228-E231,
1987
30.
Lönnroth, P,
and
Strindberg L.
Validation of the "internal reference technique" for calibrating microdialysis catheters in situ.
Acta Physiol Scand
153:
375-380,
1995[ISI][Medline].
31.
Mossberg, KA,
Rowe RW,
Tewson TJ,
and
Taegtmeyer H.
Rabbit hindlimb glucose uptake assessed with positron-emitting fluorodeoxyglucose.
J Appl Physiol
67:
1569-1577,
1989
32.
Müller, M,
Holmäng A,
Andersson OK,
Eichler HG,
and
Lönnroth P.
Measurement of interstitial muscle glucose and lactate concentrations during an oral glucose tolerance test.
Am J Physiol Endocrinol Metab
271:
E1003-E1007,
1996
33.
Müller, M,
Schmid R,
Nieszpaur-Los M,
Fassolt A,
Lönnroth P,
Fasching P,
and
Eichler HG.
Key metabolite kinetics in human skeletal muscle during ischaemia and reperfusion: measurement by microdialysis.
Eur J Clin Invest
25:
601-607,
1995[ISI][Medline].
34.
Nuutila, P,
Knuuti MJ,
Heinonen OJ,
Ruotsalainen U,
Teräs M,
Bergman J,
Solin O,
Yki-Järvinen H,
Voipio-Pulkki LM,
and
Wegelius U.
Different alterations in the insulin-stimulated glucose uptake in the athlete's heart and skeletal muscle.
J Clin Invest
93:
2267-2274,
1994[ISI][Medline].
35.
Nuutila, P,
Knuuti J,
Ruotsalainen U,
Koivisto VA,
Eronen E,
Teräs M,
Bergman J,
Haaparanta M,
Voipio-Pulkki LM,
and
Viikari J.
Insulin resistance is localized to skeletal but not heart muscle in type 1 diabetes.
Am J Physiol Endocrinol Metab
264:
E756-E762,
1993
36.
Nuutila, P,
Koivisto VA,
Knuuti J,
Ruotsalainen U,
Teräs M,
Haaparanta M,
Bergman J,
Solin O,
Voipio-Pulkki LM,
and
Wegelius U.
Glucose-free fatty acid cycle operates in human heart and skeletal muscle in vivo.
J Clin Invest
89:
1767-1774,
1992[ISI][Medline].
37.
Nuutila, P,
Mäki M,
Laine H,
Knuuti MJ,
Ruotsalainen U,
Luotolahti M,
Haaparanta M,
Solin O,
Jula A,
and
Koivisto VA.
Insulin action on heart and skeletal muscle glucose uptake in essential hypertension.
J Clin Invest
96:
1003-1009,
1995[ISI][Medline].
38.
Nuutila, P,
Raitakari M,
Laine H,
Kirvelä O,
Takala T,
Utriainen T,
Mäkimattila S,
Pitkänen OP,
Ruotsalainen U,
Iida H,
Knuuti J,
and
Yki-Järvinen H.
Role of blood flow in regulating insulin-stimulated glucose uptake in humans. Studies using bradykinin, [15O]water, and [18F]fluoro-deoxy-glucose and positron emission tomography.
J Clin Invest
97:
1741-1747,
1996
39.
Paaske, WP.
Capillary permeability in skeletal muscle.
Acta Physiol Scand
101:
1-14,
1977[ISI][Medline].
40.
Paaske, WP,
and
Sejrsen P.
Permeability of continuous capillaries.
Dan Med Bull
36:
570-590,
1989[ISI][Medline].
41.
Patlak, CS,
and
Blasberg RG.
Graphical evaluation of blood-to-brain transfer constants from multiple-time uptake data. Generalizations.
J Cereb Blood Flow Metab
5:
584-590,
1985[ISI][Medline].
42.
Patlak, CS,
Blasberg RG,
and
Fenstermacher JD.
Graphical evaluation of blood-to-brain transfer constants from multiple-time uptake data.
J Cereb Blood Flow Metab
3:
1-7,
1983[ISI][Medline].
43.
Phelps, ME,
Hoffman EJ,
Selin C,
Huang SC,
Robinson G,
MacDonald N,
Schelbert H,
and
Kuhl DE.
Investigation of [18F]2-fluoro-2-deoxyglucose for the measure of myocardial glucose metabolism.
J Nucl Med
19:
1311-1319,
1978[ISI][Medline].
44.
Raitakari, M,
Knuuti MJ,
Ruotsalainen U,
Laine H,
Makelä P,
Teräs M,
Sipilä H,
Niskanen T,
Raitakari OT,
and
Iida H.
Insulin increases blood volume in human skeletal muscle: studies using [15O]H2O and positron emission tomography.
Am J Physiol Endocrinol Metab
269:
E1000-E1005,
1995
45.
Raitakari, M,
Nuutila P,
Ruotsalainen U,
Teräs M,
Eronen E,
Laine H,
Raitakari OT,
Iida H,
Knuuti MJ,
and
Yki-Järvinen H.
Relationship between limb and muscle blood flow in man.
J Physiol (Lond)
496:
543-549,
1996[Abstract].
46.
Ruotsalainen, U,
Raitakari M,
Nuutila P,
Oikonen V,
Sipila H,
Teräs M,
Knuuti MJ,
Bloomfield PM,
and
Iida H.
Quantitative blood flow measurement of skeletal muscle using oxygen-15-water and PET.
J Nucl Med
38:
314-319,
1997[Abstract].
47.
Schelbert, HR,
Phelps ME,
Hoffman E,
Huang SC,
and
Kuhl DE.
Regional myocardial blood flow, metabolism and function assessed noninvasively with positron emission tomography.
Am J Cardiol
46:
1269-1277,
1980[Medline].
48.
Selberg, O,
Radoch E,
Walter GF,
and
Muller MJ.
Skeletal muscle glycogen content in patients with cirrhosis.
Hepatology
20:
135-141,
1994[ISI][Medline].
49.
Sokoloff, L,
Reivich M,
Kennedy C,
Des RM,
Patlak CS,
Pettigrew KD,
Sakurada O,
and
Shinohara M.
The [14C]deoxyglucose method for the measurement of local cerebral glucose utilization: theory, procedure, and normal values in the conscious and anesthetized albino rat.
J Neurochem
28:
897-916,
1977[ISI][Medline].
50.
Spinks, TJ,
Jones T,
Gilardi MC,
and
Heather JD.
Physical performance of the latest generation of commercial positron scanner.
IEEE T Nucl Sci
35:
721-725,
1988.
51.
Stallknecht, B,
Madsen J,
Galbo H,
and
Bülow J.
Evaluation of the microdialysis technique in the dog fat pad.
Am J Physiol Endocrinol Metab
276:
E588-E595,
1999
52.
Trap-Jensen, J,
and
Lassen NA.
Capillary permeability for smaller hyrophilic tracers in exercising skeletal musclein man and in patients with long-term diabetes mellitus.
In: Capillary Permeability, edited by Crone C,
and Lassen NA. Copenhagen, Denmark: Munksgaard, 1970, p. 135-152.
53.
Trap-Jensen, J,
and
Lassen NA.
Restricted diffusion in skeletal muscle capillaries in man.
Am J Physiol
220:
371-376,
1971[ISI][Medline].
54.
Utriainen, T,
Takala T,
Luotolahti M,
Rönnemaa T,
Laine H,
Ruotsalainen U,
Haaparanta M,
Nuutila P,
and
Yki-Järvinen H.
Insulin resistance characterizes glucose uptake in skeletal muscle but not in the heart in NIDDM.
Diabetologia
41:
555-559,
1998[ISI][Medline].
55.
Virkamäki, A,
Daniels MC,
Hämäläinen S,
Utriainen T,
McClain D,
and
Yki-Järvinen H.
Activation of the hexosamine pathway by glucosamine in vivo induces insulin resistance in multiple insulin sensitive tissues.
Endocrinology
138:
2501-2507,
1997
56.
Wagner, HN,
Szabo Z,
and
Buchanan JW.
Radiotracer production. Fluorine-18 compounds.
In: Principles of Nuclear Medicine. Philadelphia, PA: Sanders, 1995, p. 178-194.