Decreased permeability surface area for glucose in obese women with postprandial hyperglycemia: no effect of phosphodiesterase-5 (PDE-5) inhibition.

Insulin-mediated microvascular recruitment is recognized as a potential mechanism contributing to insulin resistance. In this study, we compared a marker of microvascular function, the permeability surface area for glucose (PS(glu)), and forearm glucose uptake after an OGTT in obese women with impaired glucose metabolism and healthy lean nondiabetic women, with the aim to characterize whether decreased permeability surface area for glucose or decreased glucose uptake may contribute to postprandial hyperglycemia in the obese group. In addition, we evaluated whether the phosphodiesterase-5 (PDE-5) inhibitor tadalafil, in a randomized double blind placebo controlled design, might attenuate postprandial glucose levels in obese women. For these purposes, intramuscular microdialysis, blood sampling from arterial and venous blood of the forearm, and measurements of forearm blood flow were performed. The results showed an impaired permeability surface area for glucose (IAUC PS(glu) 31±13 vs. 124±31; p<0.05) in obese when compared with lean participants, but no differences in forearm glucose uptake appeared between the groups. Furthermore, a single dose of tadalafil 10 mg showed no improvement of the permeability surface area for glucose, glucose uptake, or circulating glucose levels in obese participants. In conclusion, the postprandial PS(glu) response was impaired in obese women showing postprandial hyperglycemia, indicating a compromised microcirculation. However, we were unable to demonstrate any acute effect on either vascular function or glucose uptake of the phosphodiesterase-5 (PDE-5) inhibitor tadalafil.

Impaired delivery of insulin to adipose tissue and skeletal muscle in obese women with postprandial hyperglycemia.

CONTEXT: An impaired transfer of insulin from the circulation to the interstitial fluid has been suggested to contribute to insulin resistance. OBJECTIVE: The objective of the study was to address whether the delivery of insulin from the circulation to adipose tissue and skeletal muscle is impaired in obese women with postprandial hyperglycemia compared with lean healthy controls. DESIGN, SETTING, AND PARTICIPANTS: Seven obese nondiabetic women with postprandial hyperglycemia and nine lean healthy women were recruited. The interstitial insulin concentration in adipose tissue and muscle tissue was measured by the microdialysis technique during an oral glucose tolerance test (75 g). In parallel, arterial insulin levels were measured. We used ¹³³Xe clearance and plethysmography to monitor blood flow. Subcutaneous needle biopsies were taken to obtain fat cell size. RESULTS: After oral glucose ingestion, mean arterial insulin levels were higher in obese women than in the lean group. However, interstitial insulin levels in sc adipose tissue and forearm muscle were similar in both groups. Accordingly, the proportion of circulating insulin being transported across the vascular endothelium to the interstitial fluid in adipose tissue and in muscle tissue was significantly lower in the obese compared with the lean group. CONCLUSIONS: Obese subjects with postprandial hyperglycemia need higher circulating insulin levels than lean controls to attain similar interstitial insulin levels in adipose tissue and skeletal muscle, indicating an impaired transfer of insulin across the endothelium.

Tadalafil increases muscle capillary recruitment and forearm glucose uptake in women with type 2 diabetes.

AIMS/HYPOTHESIS: Recent evidence suggests that reduced synthesis of nitric oxide in endothelial cells, i.e. endothelial dysfunction, contributes to the impaired action of insulin in the vasculature of patients with type 2 diabetes. We investigated whether selective inhibition of phosphodiesterase-5 by tadalafil has beneficial effects on peripheral microcirculation and glucose uptake in these patients. METHODS: We enrolled seven postmenopausal women with type 2 diabetes and ten age-matched healthy women as controls in a placebo-controlled study to evaluate the acute metabolic effects of tadalafil. We performed microdialysis and blood flow measurements in muscle, and sampled arterial and deep venous blood before and after a single dose of tadalafil 20 mg or placebo. Circulating glucose and insulin levels, muscle capillary recruitment as reflected by permeability surface area for glucose (PS(glu)) and forearm glucose uptake were measured. RESULTS: In women with type 2 diabetes, but not in the control group, tadalafil induced increases in the incremental AUC for PS(glu) (tadalafil vs placebo 41 +/- 11 vs 4 +/- 2 ml [100 g](-1) min(-1), p < 0.05) and forearm glucose uptake (46 +/- 9 vs 8 +/- 4 micromol [100 g](-1) min(-1), p < 0.05). The variable that best predicted forearm glucose uptake was PS(glu), which explained 70% of its variance. However, fasting glucose and insulin concentrations were similar following treatment with placebo or tadalafil in the two groups. CONCLUSIONS/INTERPRETATION: This study suggests that tadalafil evokes positive metabolic effects in insulin-resistant women with type 2 diabetes.

Laser-Doppler flowmetry reveals rapid perfusion changes in adipose tissue of lean and obese females.

The present study aimed to evaluate adipose tissue blood flow (ATBF) by means of laser-Doppler flowmetry (LDF) in humans. Lower body negative pressure (LBNP) and straining known to affect epidermal blood flow through the autonomic nervous system were performed in 11 lean and 11 obese female volunteers. ATBF changes were compared between both groups and also discriminated from skin blood flow (SBF) responses of the immediate vicinity. Additionally, LDF measurements were compared with flow measurements using (133)xenon washout in 10 lean subjects during whole body cooling. LDF estimations of SBF and ATBF showed a positive correlation to (133)Xe during cooling. SBF and ATBF were reduced to the same extent in both lean and obese subjects during LBNP. Straining induced divergent changes in SBF and ATBF: initially SBF decreased while ATBF increased, but toward the end of straining SBF increased above baseline and ATBF returned down to baseline level. Those changes were similar in both weight groups. Interestingly, only in obese subjects, both LBNP and straining were followed by ATBF augmentation, while SBF levels remained stable. In conclusion, LDF compares with (133)Xe washout in monitoring ATBF during tonic perfusion changes. Its strength, however, lies in the detection of rapid flow alterations within the subcutaneous tissue, allowing the evaluation of reflex responses of the subcutaneous microcirculation. Interestingly, those rapid changes in SBF and ATBF can be both concordant and discordant. With regard to ATBF, vasoconstrictor components of the reflex responses were similar in lean and obese subjects, whereas vasodilatory responses were more pronounced in obese volunteers.

Regulation and counterregulation of lipolysis in vivo: different roles of sympathetic activation and insulin.

To obtain further information on the regulation of lipolysis in vivo, the effect of increasing sympathetic nerve activity via lower body negative pressure (LBNP, -20 mm Hg) was studied in 11 healthy human subjects. Subcutaneous and muscle microdialysis as well as blood flow measurements were performed in the postabsorptive state and during an euglycemic hyperinsulinemic clamp. LBNP for 30 min in the postabsorptive phase resulted in an approximately 50% increase (P < 0.005) in the interstitial-arterial concentration difference for glycerol in adipose tissue, whereas no such effect was registered in muscle. Blood flow in adipose tissue and the forearm remained unaltered. During euglycemic hyperinsulinemic conditions (p-insulin 645 +/- 62 pmol/liter), both interstitial adipose tissue and arterial concentrations of glycerol were reduced. LBNP resulted in an increase in interstitial-arterial concentration difference in glycerol similar to that seen in the postabsorptive state (approximately 50%, P < 0.05). Muscle glycerol was not changed by either insulin or LBNP. Glucose infusion rate during the clamp was significantly decreased during LBNP (7.82 +/- 0.88 vs. 8.67 +/- 1.1 ml/kg.min, P < 0.05). We conclude that the sympathetic nervous activation by LBNP results in an increased lipolysis rate in adipose tissue both in the postabsorptive phase and during insulin infusion. On the other hand, muscle glycerol output was not affected by either LBNP or insulin. The data suggest that 1) lipolysis is regulated differently in muscle and adipose tissue, 2) postabsorptive lipolysis is mainly regulated by insulin, and 3) sympathetic nervous activation effectively inhibits the antilipolytic action of insulin by inducing insulin resistance.

Sympathetic control of white adipose tissue in lean and obese humans.

AIM: To induce lipolysis, catecholamines could reach the adipocyte via the blood stream after being released from the adrenal medulla or, alternatively, via neuronal release in the vicinity of the fat cell. Sympatho-neuronal effects on fat tissue lipolysis have been demonstrated in experimental animal models. However, the role of sympathetic nerves in the control of lipolysis in human white adipose tissue, which is sparsely innervated, has not been clarified. CONCLUSION: The present review summarizes evidence for a direct neuronal influence on lipolysis in humans.

Validation of a glucose-insulin-potassium infusion algorithm in hospitalized diabetic patients.

OBJECTIVES: Validation of a novel glucose-insulin-potassium (GIK) infusion algorithm to optimize metabolic control in hospitalized diabetic patients. SUBJECTS: We randomized 33 diabetic patients admitted to Sahlgrenska University Hospital with acute internal medicine diseases to either GIK infusion or multiple injection therapy (MIT). The GIK infusion rate and the MIT were controlled according to special algorithms. The treatment efficacy was evaluated through comparisons of capillary blood glucose eight times on day 2 of the study. RESULTS: The GIK infusion led to significantly lower mean blood glucose when compared with MIT [10.1 (9.0-11.2) vs. 12.3 (9.3-14.4) mmol L(-1), median and interquartile range, P < 0.01]. Four episodes of hypoglycaemia without loss of consciousness were recorded in the GIK group whereas no hypoglycaemic event occurred in the MIT group. A mean of 1 (1-3) episodes of blood glucose levels above 12.0 mmol L(-1) were recorded in the GIK group compared with 3.5 (1.5-5.0) in the MIT group, P < 0.01. CONCLUSIONS: The algorithm used for the GIK infusion gave an acceptable level of metabolic control and this insulin infusion protocol is safe enough to be used by the nursing staff on a general internal medicine ward.

Determination of Lewis FUT3 gene mutations by PCR using sequence-specific primers enables efficient genotyping of clinical samples.

We have developed a polymerase chain reaction method using sequence-specific primers (PCR-SSP) for rapid and correct genotyping of the common Lewis (FUT3) gene mutations 59T>G, 202T>C, 314C>T, 508G>A, and 1067T>A. The PCR-SSP method was validated on 20 healthy blood donors and 16 non-insulin-dependent diabetic patients. All individuals were in parallel genotyped by our established polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis. The FUT3 genotypes, determined with the PCR-SSP method, were in complete accordance with the results of the PCR-RFLP reference method. The PCR-SSP method could also be adapted to assign the presence of a specific mutation to the respective FUT3 alleles. We found the method to be reliable, rapid and cheap with no requirements for restriction enzyme processing.

Lactate and glycerol release from adipose tissue in lean, obese, and diabetic women from South Africa.

Abnormalities observed in intermediary metabolism may be related to the pathogenesis of obesity-related diseases such as type 2 diabetes. Glycerol and lactate production was estimated in the sc adipose tissue of two anatomical regions of 10 lean (LW), 10 obese (OW), and 10 matched diabetic (DW) black urban women. This was done with the sc microdialysis technique and combined with adipose tissue blood flow (ATBF) rates calculated from (133)Xe clearance. Biochemical measurements were made in the postabsorptive and postprandial state. Bioimpedance and computed tomography scans were used to define body composition. DW present with more visceral fat (DW, 138 +/- 5.0; OW, 66.6 +/- 5.0 cm; P < 0.01). This was associated with elevated free testosterone levels (DW, 1.21 +/- 0.1; OW, 0.75 +/- 0.1 nmol/L; P < 0.05). The fasting FFA, glycerol, and lactate levels increased across the three groups (LW < OW < DW). During the oral glucose tolerance test, glucose levels were elevated in DW, with higher insulin levels [0 h: DW, 207 +/- 8.6; OW, 100 +/- 7.2 pmol/L (P < 0.01); 1 h: DW, 410 +/- 15.2; OW, 320 +/- 10.9 pmol/L (P < 0.05)], but with a flat Cpeptide response (1 h: DW, 932 +/- 40; OW, 1764 +/- 40 pmol/L; P < 0.05). Plasma lactate levels increased significantly in LW and OW at 1 h (P < 0.001), but remained lower in LW vs. OW for all time points. ATBF was highest in LW [abdominal, 0 h: DW, 4.5 +/- 0.2; OW, 1.7 mL/100 g.min (P < 0.01); femoral, 0 h: DW, 3.4 +/- 0.2; OW, 1.8 +/- 0.3 mL/100 g.min (P < 0.01)]. ATBF did not increase in DW during the oral glucose tolerance test. Glycerol release (GR) was used to assess the lipolytic rate and was highest in LW in the abdominal area [0 h: LW, 1.7 +/- 0.2; OW, 1.1 +/- 0.2 micromol/kg.min (P < 0.05); DW, 0.78 +/- 0.05 micromol/kg.min (P < 0.05 vs. OW)]. By contrast, GR was higher in the femoral area of OW (0 h: OW, 1.6 +/- 0.2; LW, 1.15 +/- 0.1 micromol/kg.min; P < 0.05). Regional differences were observed for GR in both OW and DW (femoral > abdominal). Lactate release (LR) was low in DW [abdominal, 0 h: DW, 3.5 +/- 0.4; OW, 7.8 +/- 1.0 micromol/kg.min (P < 0.001); femoral, 0 h: DW, 3.1 +/- 0.3; OW, 9.0 +/- 0.9 micromol/kg.min (P < 0.001)]. LR was appropriately low for body fat mass in LW, with a brisk increase between 0 and 1.5 h. A negative correlation exists between GR (abdominal area) and insulin levels in the postabsorptive state (P < 0.0001). In conclusion, 1) the fasting lipolytic rate is associated with insulin levels; 2) OW and DW have more adipose tissue insulin resistance than LW; 3) OW and DW have a brisker lipolysis in the femoral area; and 4) in DW, higher visceral mass is associated with elevated free testosterone and FFA concentrations. Obesity in the black population is therefore characterized by a marked degree of adipose tissue lipolysis. This degree of resistance together with increasing body fat mass may predispose the obese women to developing type 2 diabetes. Once this disease is established, the onset of adipose tissue vascular insulin resistance will sustain ongoing insulin resistance, even in the presence of relative insulinopenia.

Insulin insensitivity and delayed transcapillary delivery of insulin in oophorectomized rats treated with testosterone.

The importance of transcapillary insulin delivery as a regulated step was explored in an insulin resistant rat model. Oophorectomized female rats were exposed to testosterone (OVX + T) for 8 weeks and examined with insulin clamps, muscle microdialysis, and analyses of insulin distribution kinetics. The results were compared with those obtained in sham-operated control rats. After OVX + T, onset of glucose uptake in skeletal muscle was significantly (P < 0.001-0.05) delayed compared with controls as measured by the glucose infusion rate (GIR) during a euglycaemic, hyperinsulinaemic clamp (5 mU kg-1 min-1). The increase in interstitial insulin concentrations was also significantly (P < 0.05) delayed (15-20% lower) in OVX + T treated rats compared with control rats, but to such a small magnitude that this alone could not explain the late onset of the insulin effect. Skeletal muscle capillary density, examined histochemically, was diminished (P < 0.01-0.001) by 20-25% after treatment with OVX + T compared with control animals, as was the peripheral blood flow (P < 0.05) by 40-45%, measured with the microsphere technique. Insulin binding was reduced in proportion to the reduced (P < 0.01) vascular surface area by OVX + T treatment. Transcapillary transport rate of insulin, measured by comparisons of the kinetics of inulin and insulin spaces in muscle with time, tended (ns) to be lower after OVX + T compared with control rats (30-40%) as a reflection of the lower capillary surface area. The data suggest that the delayed onset of insulin action after OVX + T results from combined defects in the muscle cell at a postreceptor level and, to a lesser extent, from retarded transcapillary delivery of insulin.

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

AIMS/HYPOTHESIS: To determine the lumped constant (LC), which accounts for the differences in the transport and phosphorylation between [(18)F]-2-fluoro-2-deoxy-d-glucose ([(18)F]FDG) and glucose, for [(18)F]FDG in human adipose tissue. METHODS: [(18)F]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 [(18)F]FDG uptake (rGUFDG) and femoral muscle glucose uptake were measured using [(18)F]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 micromol/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: [(18)F]FDG-PET seems a feasible tool to investigate adipose tissue glucose metabolism in human beings. Direct measurements with [(18)F]FDG-PET and microdialysis suggest a LC value of 1.14 for [(18)F]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.

Evidence for insulin resistance in black women from South Africa.

OBJECTIVE: The rate of glucose disposal was determined in 10 black and 10 white obese nondiabetic urban women from South Africa to assess insulin resistance. DESIGN AND METHODS: Euglycemic hyperinsulinemic clamp and body composition analysis. RESULTS: Age, body mass index (BMI), anthropometric measurements and body composition were similar in both groups of women. A five-level computed tomography (CT) scan showed a similar mean subcutaneous fat mass in both groups of women (black obese women 555 +/- 9.0 vs white obese women 532 +/- 6.0 cm2), but less visceral fat in black obese women (90 +/- 3.0 vs 121 +/- 3.1 cm2; P< 0.05). Black obese women had higher fasting free fatty acid (997 +/- 69 vs 678 +/- 93 micromol/l; P < 0.05) and lactate concentrations (1,462 +/- 94 vs 1,038 +/- 39 micromol/l; P < 0.05), but lower fasting insulin levels (87 +/- 12 vs 155 +/- 9 pmol/l; P < 0.001). Black obese women also had a more favorable HDL: total cholesterol ratio (30.5% vs 23.0%; P< 0.04). The mean glucose disposal rate (M) and disposal expressed as glucose sensitivity index (M/I) were reduced in the black obese women vs white obese women (M: 7.1 +/- 0.8 vs 13.7 +/- 1.0 mmol/kg min(-1) x 100; P< 0.01, and M/I: 0.12 +/- 0.01 vs 0.24 +/- 0.02 mmol/kg x min(-1)/pmol/1 x 1,000; P < 0.01). Only black obese women showed a significant decrease in C-peptide levels during the clamp (2.9 +/- 0.22 vs 1.2 +/- 0.12 nmol/l; P<0.001). During the euglycemic period, the black obese women had higher lactate levels at all time points, but only the white obese women had increased lactate levels (918 +/- 66 to 1,300 +/- 53 micromol/l; P< 0.05). CONCLUSION: Black obese women demonstrate a higher degree of insulin resistance, despite less visceral fat and a higher HDL: total-cholesterol ratio. In addition, endogenous beta-cell secretory function in black obese women appears to be more sensitive to the suppressive effect of exogenous insulin administration. The significant increase in lactate levels in white obese women confirms that they are more insulin sensitive.

The subcutaneous lipolytic response to regional neural stimulation is reduced in obese women.

Disturbed fat tissue metabolism with a reduction of the lipolytic rate could be an important pathogenetic factor in obesity. Lipolysis of the subcutaneous tissue of the thigh is partly under neural control and can be increased by intraneural stimulation of the lateral cutaneous femoral nerve in lean women. In the present study, we tested whether the lipolytic response to intraneural stimulation is altered in vivo in obese subjects. Seven obese women were examined and the results were compared with those of seven age-matched lean women. After an overnight fast, the lateral cutaneous femoral nerve was intraneurally stimulated for 10 min, and the local subcutaneous lipolytic response to this procedure was evaluated with microdialytic measurements of interstitial glycerol concentrations in the receptive field of the stimulated nerve fascicle. To exclude unspecific effects of stimulation, lipolysis was also controlled in a corresponding area of the contralateral leg. Intraneural stimulation produced no significant change in subcutaneous lipolysis in obese women (25.7 +/- 9.7%, NS). This finding is in sharp contrast with the marked regional lipolytic response in lean women in which the same stimulation procedure enhanced the regional interstitial glycerol levels by 72 +/- 17% (P < 0.05) compared with the unstimulated corresponding area of the contralateral leg. These in vivo results suggest that human obesity is characterized by a profound unresponsiveness of the subcutaneous adipose tissue to neurally stimulated lipolysis. This could be an important factor in the development and treatment of obesity.

Estimations of muscle interstitial insulin, glucose, and lactate in type 2 diabetic subjects.

Previous measurement of insulin in human muscle has shown that interstitial muscle insulin and glucose concentrations are approximately 30-50% lower than in plasma during hyperinsulinemia in normal subjects. The aims of this study were to measure interstitial muscle insulin and glucose in patients with type 2 diabetes to evaluate whether transcapillary transport is part of the peripheral insulin resistance. Ten patients with type 2 diabetes and ten healthy controls matched for sex, age, and body mass index were investigated. Plasma and interstitial insulin, glucose, and lactate (measured by intramuscular in situ-calibrated microdialysis) in the medial quadriceps femoris muscle were analyzed during a hyperinsulinemic euglycemic clamp. Blood flow in the contralateral calf was measured by vein plethysmography. At steady-state clamping, at 60-120 min, the interstitial insulin concentration was significantly lower than arterial insulin in both groups (409 +/- 86 vs. 1,071 +/- 99 pmol/l, P < 0.05, in controls and 584 +/- 165 vs. 1, 253 +/- 82 pmol/l, P < 0.05, in diabetic subjects, respectively). Interstitial insulin concentrations did not differ significantly between diabetic subjects and controls. Leg blood flow was significantly higher in controls (8.1 +/- 1.2 vs. 4.4 +/- 0.7 ml. 100 g(-1).min(-1) in diabetics, P < 0.05). Calculated glucose uptake was less in diabetic patients compared with controls (7.0 +/- 1.2 vs. 10.8 +/- 1.2 micromol. 100 g(-1).min(-1), P < 0.05, respectively). Arterial and interstitial lactate concentrations were both higher in the control group (1.7 +/- 0.1 vs. 1.2 +/- 0.1, P < 0. 01, and 1.8 +/- 0.1 vs. 1.2 +/- 0.2 mmol/l, P < 0.05, in controls and diabetics, respectively). We conclude that, during hyperinsulinemia, muscle interstitial insulin and glucose concentrations did not differ between patients with type 2 diabetes and healthy controls despite a significantly lower leg blood flow in diabetic subjects. It is suggested that decreased glucose uptake in type 2 diabetes is caused by insulin resistance at the cellular level rather than by a deficient access of insulin and glucose surrounding the muscle cell.

Lumped constant for [(18)F]fluorodeoxyglucose in skeletal muscles of obese and nonobese humans.

Quantitative 2-[(18)F]fluoro-2-deoxy-D-glucose ([(18)F]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 [(18)F]FDG and glucose. In this study, we estimated the LC for [(18)F]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/m(2)] and eight nonobese (age 25.0 +/- 1.0 yr, BMI 23.1 +/- 1.0 kg/m(2)) males were studied during euglycemic hyperinsulinemia (1 mU. kg(-1).min(-1) for 150 min). Muscle blood flow was measured using (15)O-labeled water and PET. Muscle [(18)F]FDG uptake (rGU(FDG)) was calculated with Patlak graphic analysis. Interstitial glucose concentration of the quadriceps femoris muscle was measured simultaneously with [(18)F]FDG scanning using microdialysis. Muscle glucose uptake (by microdialysis, rGU(MD)) was calculated by multiplying glucose extraction by regional muscle blood flow. A significant correlation was found between rGU(MD) and rGU(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 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 [(18)F]FDG in human skeletal muscle during insulin stimulation, and the LC appears not to be sensitive to insulin resistance.

Delta-aminolevulinic acid in superficial basal cell carcinomas and normal skin-a microdialysis and perfusion study.

Delta-aminolevulinic acid (ALA) is used for photodynamic therapy of basal cell carcinoma (BCC) as it is converted to protoporphyrin IX in tumour tissue. During illumination with 635 nm light a photochemical reaction takes place, singlet oxygen is generated and the tumour destroyed. In this study we used the microdialysis technique to quantify the concentration of ALA at a certain depth in tumour and healthy skin. The penetration ability of ALA was investigated as a function of time in BCCs (n = 14) and in normal skin (n = 4) after topical application. The microdialysis catheters were inserted intracutaneously and the depth position recorded by means of ultrasound. Microdialysate sample concentrations of amino acids and ALA were determined by high performance ion-exchange chromatography. A laser Doppler perfusion imager measured perfusion in the BCCs. The data show that the average depth of the microdialysis catheters was 0.5 mm. The interstitial ALA concentration in the BCCs increased from 0 to 3.1 mmol/L 15 min after application of ALA, whereas no measurable amounts of ALA were found in healthy skin. The blood perfusion was 2.5-fold increased in the BCCs. The interstitial levels of amino acids were not significantly changed during the ALA treatment. In summary, we found that ALA rapidly penetrates tumour skin. We conclude that microdialysis seems to be well suited for pharmacodynamic studies of ALA in skin.

Validation of an endogenous reference technique for the calibration of microdialysis catheters.

In order to validate the use of urea as an internal reference for the calibration of microdialysis catheters, both subcutaneous and muscle measurements were taken in 11 healthy volunteers. The equilibration calibration of urea, glucose and lactate, and the internal reference (3H-glycerol retrodialysis) calibration of glycerol were performed in both the muscle and fat. These data were then compared with those taken from the arterial plasma. Based on the average arterial-interstitial fluid concentration difference, the urea microdialysis relative recovery was estimated from dialysate and plasma content of urea. Interstitial urea was then used as an endogenous reference for the calculation of the relative recovery of each substance. This was carried out after defining the relative recovery ratios (RR) that were obtained from in vitro measurements on crystalline solutions with the assumption that RR in vivo = RR in vitro. The data demonstrate that the interstitial fluid concentrations of glucose, lactate and glycerol can be calculated from the knowledge of plasma and microdialysate content of urea together with the RR in vitro. Also, the data that were obtained using urea as an endogenous reference showed a significant correlation with those that were achieved using either equilibration or internal reference (retrodialysis) techniques for calibrating the microdialysis devices.

Muscle glucose uptake is effectively activated by ischemia in type 2 diabetic subjects.

It has previously been shown that Wortmannin, a phosphatidylinositol 3-kinase inhibitor, inhibits glucose transport activated by insulin but not by ischemia, suggesting the importance of an activating mechanism that bypasses the insulin signal. To evaluate the relevance of this insulin-independent pathway in insulin-resistant subjects, the ability of ischemia to stimulate glucose uptake was investigated in 9 patients with type 2 diabetes and in 9 healthy control subjects (fasting glucose level 9.4 +/- 0.8 vs. 5.1 +/- 0.1 mmol/l, P < 0.001, in type 2 diabetic patients and control subjects, respectively; fasting insulin level insulin 8.1 +/- 2.6 vs. 4.5 +/-0.7 mU/l, P < 0.05, respectively) matched for sex, age, and BMI. Arterial plasma and interstitial concentrations of glucose and lactate (measured by subcutaneous and muscle microdialysis) were recorded in the forearm before, during, and after ischemia induced locally for 20 min. During ischemia, the muscle interstitial glucose concentration decreased significantly from 7.7 +/- 0.6 to 5.4 +/- 0.4 mmol/l (P < 0.01) and from 4.4 +/- 0.3 to 3.6 +/- 0.3 mmol/l (P < 0.05) in type 2 diabetic patients and control subjects, respectively. The arterial-interstitial (A-I) glucose concentration difference was 1.7 +/- 0.6 and 0.7 +/- 0.3 mmol/ at basal, and it increased significantly to 3.5 +/- 0.7 (P < 0.01) and 1.4 +/-0.3 mmol/l (P < 0.05) during ischemia in each group, respectively. Interstitial lactate increased significantly during ischemia from 0.8 +/- 0.1 to 1.1 +/- 0.1 mmol/l (P < 0.05) and from 0.5 +/- 0.1 to 0.9 +/- 0.2 mmol/l (P < 0.05), respectively. The A-I glucose concentration difference was abolished immediately postischemia and regained after approximately 15 min, whereas high interstitial lactate levels remained elevated throughout the study. Subcutaneous interstitial glucose concentrations remained unchanged during ischemia and postischemia in both groups, whereas the interstitial lactate concentration in adipose tissue increased during ischemia from 1.4 +/- 0.2 to 2.0 +/- 0.2 mmol/l (P < 0.05) and from 1.1 +/- 0.1 to 1.8 +/- 0.3 mmol/l (P < 0.05) in type 2 diabetic patients and control subjects, respectively. Plasma glucose and lactate levels were unchanged in both groups during the study period. The results show that in muscle, but not in adipose tissue, glucose uptake is efficiently activated by ischemia in insulin-resistant type 2 diabetic subjects, suggesting the activation of a putative alternative pathway to the insulin signal in muscle cells.

Effects of exercise on insulin distribution and action in testosterone-treated oophorectomized female rats.

Administration of testosterone (T) to oophorectomized (Ovx) female rats is followed by severe insulin resistance, localized to postreceptor cellular events in the muscle. In this study, intervention by exercise was introduced to examine whether circulatory adaptations are involved in insulin resistance. Two groups of Ovx rats were studied: one group was given T (Ovx+T); another group had free access to running wheels (Ovx+T+Ex). In addition, one control group (sham operated) was studied. Insulin sensitivity was measured with the euglycemic hyperinsulinemic clamp technique (submaximal) for 150 min. Muscle interstitial glucose and insulin concentrations were measured by microdialysis. The measurements showed that, in Ovx+T rats, the onset of insulin action was significantly (P < 0.05) slower during the first 95 min of the clamp compared with that in Ovx+T+Ex and controls. Muscle interstitial concentrations of insulin but not glucose were lower in both Ovx+T and Ovx+T+Ex rats than in controls throughout the clamp. It was concluded that physical exercise prevented the slow onset of insulin action in Ovx+T rats without changing the distribution time of muscle interstitial insulin. The results indicate that hyperandrogenicity is characterized by delayed muscle insulin action. Physical exercise reverses these defects without any beneficial effect on muscle interstitial insulin concentrations.

No difference in the lipolytic response to beta-adrenoceptor stimulation in situ but a delayed increase in adipose tissue blood flow in moderately obese compared with lean men in the postexercise period.

This study was undertaken to determine the effect of previous exercise on adipose tissue responsiveness to beta-adrenoceptor stimulation and on adipose tissue blood flow (ATBF). Eight lean and 8 obese men (body mass index [BMI], 23.6 +/- 2.1 [SD] v 29.0 +/- 1.9 kg x m(-2)) were investigated with abdominal subcutaneous microdialysis and 133Xe clearance. A stepwise isoprenaline infusion (10(-8), 10(-7), and 10(-6) mol x L(-1)) was administered in situ in the microdialysis catheter before and 2 hours after a submaximal exercise bout (90 minutes of cycling at 55% of maximal O2 uptake). No differences in the response (increase in interstitial glycerol v preinfusion level) to isoprenaline infusions were found between the 2 groups. In both groups, there was no difference in the response to postexercise versus preexercise infusion. When the vasodilating agent hydralazine (0.125 g x L(-1)) was infused into the microdialysis catheter to control for the vascular effects of isoprenaline, an interaction effect between exercise and isoprenaline dose was found. Analyses showed an attenuated response to the high isoprenaline dose after exercise (lean, 251 +/- 42 [SE] micromol x L(-1); obese, 288 +/- 77 micromol x L(-1)) versus before exercise (lean, 352 +/- 62 micromol x L(-1), P = .045 v after; obese, 380 +/- 94 micromol x L(-1), P = .021 v after), indicating a desensitization of lipolysis to beta-adrenoceptor stimulation. ATBF and arterial plasma glycerol increased after exercise in both groups, but the increase was delayed in obese subjects. Arterial plasma insulin was higher in the obese versus lean subjects at all times, and decreased during recovery in both groups. In conclusion, abdominal subcutaneous adipose tissue responsiveness to beta-stimulation is not enhanced postexercise in lean and obese men, whereas previous exercise increases ATBF. Furthermore, the data suggest slower lipid mobilization postexercise and resistance to the antilipolytic effect of insulin in the obese.