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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.

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.

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.

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.

The in vitro effects of cortisol and GH on basal and stimulated lipolysis in human adipose tissue were studied using a tissue incubation technique. After preincubation for 3 days in control medium containing insulin, adipose tissue pieces were exposed to cortisol for 3 days. GH was added to the cortisol-containing medium during the last 24 h (day 6). Adipocytes were then isolated, and lipolysis was studied in the absence and presence of isoprenaline, noradrenaline, forskolin, and N-6-monobutyryl-cAMP. Cortisol reduced the basal rate of lipolysis (P < 0.01) and the sensitivity to isoprenaline compared to the control values (P < 0.01). Addition of GH to the cortisol-containing medium increased the basal rate of lipolysis (P < 0.01) and the sensitivity to isoprenaline (P < 0.01) to the control level and increased the maximum isoprenaline-induced lipolytic activity (P < 0.01). Similar effects were obtained in the presence of noradrenaline. Maximum forskolin-induced lipolytic activity was reduced after exposure of the tissue to cortisol (P < 0.05), whereas addition of GH antagonized this effect (P < 0.01). Induction of the maximum lipolytic activity with N-6-monobutyryl-cAMP was not influenced by the preceding hormone exposure. Addition of GH alone during the last 24 h of incubation increased the basal rate of lipolysis (P < 0.05) and resulted in a borderline significant increase in the maximum isoprenaline-induced lipolytic activity (P = 0.055), suggesting that GH induces lipolysis also in the absence of glucocorticoids. Thus, cortisol and GH have opposite effects on the basal lipolytic activity in human adipose tissue in vitro as well as on the sensitivity to catecholamines, GH being the lipolytic and cortisol the antilipolytic agent. The present findings are in agreement with in vivo observations.

Objective: To investigate the relationship between leptin concentrations, various metabolic indices and body composition in six different groups., Design and Measurements: Anthropometric measurements, fasting plasma glucose, serum insulin, C-peptide, FFA and leptin levels were performed. In the obese and diabetic subjects, body composition was analysed with bio-impedance equipment and as a 5 level CT scan., Subjects: Five lipoatrophic diabetes mellitus (LDM) patients, five normal subjects (N), nine white and nine black obese women (WW, BW), and nine white and nine black diabetic women (DWW, DBW) were investigated after an overnight fast., Results: In both ethnic groups there was a positive correlation between leptin and BMI (black group: r=0.8; P<0.0001, white group: r=0.7, P<0.002) and leptin and SC fat mass (black group: r=0.6; P<0.005, white group: r=0.6; P<0.004)., Conclusions: Across the groups, there were positive linear correlations between leptin concentrations, BMI, SC fat mass and FFA levels. Leptin and FFA concentrations are higher and insulin levels lower in both groups of black women compared to the two groups of white women, despite a similar BMI and body fat mass. In the DBW the large increase in visceral fat mass may be indicative of a more complex relationship between compensatory insulin resistance, elevated FFA levels and leptin secretion.

To measure interstitial glycerol and lactate production from the sc adipose tissue of two regions in nine black and nine white lean men, sc microdialysis was performed in combination with adipose tissue blood flow rates measured with 133Xe clearance. In the postabsorptive state, the plasma glucose and insulin levels of the black men and white men were similar. The black men had higher plasma free fatty acids (825+/-97 vs. 439+/-58 micromol/L; P < 0.005), glycerol (99.5+/-5.1 vs. 54.1+/-3.3 micromol/L; P < 0.0001), and lactate (1056+/-95 vs. 729+/-45 micromol/L; P < 0.01). Interstitial glycerol concentrations in the black and white men were 227 vs. 163 micromol/L (P < 0.01) and 230 vs. 162 micromol/L (P < 0.05) in the abdominal and femoral regions. The adipose tissue blood flow rate was higher in the black men in the abdominal (7.9+/-0.9 vs. 3.1+/-0.5 mL/100 g x min; P < 0.01) and femoral area (5.2+/-0.6 vs. 2.8+/-0.3; P < 0.01). Interstitial lactate concentrations in black and white men were 1976 vs. 1364 micromol/L (P < 0.004) and 1953 vs. 1321 micromol/L (P < 0.004) in the abdominal and femoral regions, respectively. Glycerol release was higher in black men vs. white men for abdominal (0.21+/-0.02 vs. 0.14+/-0.02 micromol/100 g x min; P < 0.02) and femoral (0.22+/-0.02 vs. 0.15+/-0.01; P < 0.05) areas. Postprandially, black men had higher plasma glucose levels [1 h, 9.6+/-0.4 vs. 8.2+/-0.5 mmol/L (P < 0.05); 2 h, 8.9+/-0.4 vs. 7.2+/-0.4 mmol/L (P < 0.01)], but lower plasma insulin levels [1 h, 173+/-13 vs. 264+/-48 pmol/L (P < 0.05); 2 h, 136+/-20 vs. 209+/-34 pmol/L (P < 0.05)]. Plasma free fatty acid, lactate, and glycerol levels remained higher in the black men. After 1 h, lactate release was higher in the black men vs. that in the white men for abdominal (20.5+/-1.6 vs. 14.7+/-2.5 micromol/100 g x min;P < 0.05) and femoral (15.6+/-1.1 vs. 12.1+/-1.8; P < 0.03) areas. We conclude that the black men, who are relatively insulinopenic postprandially, have a brisker lipolysis and also release more lactate from sc fat tissue than white men. These differences in adipose tissue metabolism may be related to differences in the lipid profiles and glucose metabolism previously documented in these ethnic groups.

To determine whether neurogenic factors may be of importance in the regulation of histamine release and blood flow in psoriatic plaque, the effect of capsaicin was studied in 22 psoriatic patients with active, untreated psoriatic lesions. In each of 12 patients, one microdialysis fibre was placed in non-lesional skin and one was placed in lesional skin at depths of 0.7 and 0.9 mm, respectively. Dialysates were collected for the analysis of histamine in the resting state and after 60 min of repetitive epicutaneous application of 1% capsaicin above the microdialysis catheter. In 10 patients, topical capsaicin and placebo were applied for 24 h to lesional/lesion-free skin. Skin blood flow and perfusion (evaluated using the 133xenon clearance technique and scanning laser Doppler, respectively) were measured before the application of capsaicin and after removal. After 60 min of capsaicin treatment, both the perfusion and interstitial concentration of histamine, as well as the net release of histamine, were significantly increased in affected (from 38 +/- 6 to 45 +/- 6 nmol/L, mean +/- SEM) and unaffected (from 15 +/- 2 to 19 +/- 2 nmol/L) skin. Compared with placebo, 24 h of treatment with capsaicin caused a 15% decrease in perfusion in lesional skin. The results are compatible with the hypothesis that capsaicin-sensitive nerves may induce histamine release in non-lesional and lesional skin and that afferent unmyelinated nerve fibres may contribute to the high blood flow in psoriatic plaques.

This study aims at developing per- and postopertive surveillance of the myocardium and focuses on ischemic damage following cardioplegic heart arrest. Levels of troponin T and total aspartate aminotransferase (ASAT) were analyzed in the myocardial interstitium of 10 patients with ischemic heart disease (IHD) who underwent coronary bypass surgery and in 12 patients with nonischemic heart disease (N-IHD) who underwent valvular surgery. Fluid from the myocardial interstitium of the anterior and the lateral wall of the heart was sampled by microdialysis probes that were implanted during surgery and extracted percutaneously 70-100 h later. There were no adverse reactions, and the equipment did not interfere with the surgical procedures. The peak in troponin T serum levels that occurred 4 h after cardiac arrest was preceded by a peak in troponin T levels in the microdialysates from the interstitium that occurred 1 h earlier. The concentration of troponin T in the microdialysate peak was 300 times higher than in the serum peak. The increase in serum ASAT levels during the first 7 h after cardiac arrest corresponded in time with a decrease in interstitial ASAT levels, which had already reached a maximum during cardiac arrest. The microdialysate/serum concentration ratio was considerably smaller for ASAT than for troponin T. Interstitial peak levels of troponin T correlated positively and significantly with peak levels of ASAT. Of the 22 patients, 15 had no postoperative events according to clinical outcome, ECG and serum tests. Fourteen of these had low to normal levels of interstitial ASAT and troponin T. Conversely, atrial fibrillation and/or premature atrial contractions were recorded in 8/22 patients, 7 of whom had elevated interstitial ASAT and/or troponin T concentrations in one or both of the sampled heart regions. The N-IHD patients had higher levels of troponin T in the interstitium 20-70 h following cardioplegia, while the peak levels did not differ between the groups. In conclusion, microdialysis sampling of troponin T and ASAT is safe and allows a highly sensitive analysis of the ischemic trauma exerted by the cardioplegic arrest., (Copyright 2000 S. Karger AG, Basel)

Extracellular levels of amino acids in the myocardial interstitium are sensitive indicators of myocyte function. Lowered ATP leads to a rapid extracellular appearance of amino acids with a high intra- to extracellular concentration ratio, such as taurine and glutamate. Nitrogen fluxes are reflected by glutamine, while alanine, glycine, serine and leucine are markers of proteolysis. In addition, degradation of membrane phospholipids is reflected by other primary amines, such as phosphoethanolamine. The time course of these changes was determined before, during and after cardioplegic heart arrest. Two regions of the heart were monitored in 20 patients by means of microdialysis sampling. After only 20 min of heart arrest, extracellular taurine, glutamate and phosphoethanolamine increased transiently up to 25 times the basal level. Ten-20 min later, glutamine increased by 6 times. A doubling of alanine, glycine, serine and leucine levels took place 30 min after release of the aortic cross-clamp. After 2 h, all were at levels similar to those recorded 15-30 h later. Levels of taurine and glutamate in the anterior wall of the heart correlated significantly with those of its lateral wall. The response to surgery and heart arrest was studied in a group of patients with ischemic heart disease as well as in another group of patients, who underwent heart surgery for nonischemic reasons. The response of taurine and glutamine was significantly higher for the patients with ischemic heart disease, in spite of a shorter mean time of heart arrest. No sex differences were recorded. High levels of amino acids coincided frequently with clinical events, which were suggestive of ischemia, but were also recorded in a few patients without diagnosed events. We conclude that monitoring of extracellular amino acids is valuable for evaluation and development of cardioprotective strategies.

Previous measurements in lymph and adipose tissue have indicated that interstitial insulin concentrations are approximately 40% lower than in plasma. Measurements of insulin in human muscle interstitial fluid have not been performed yet. We developed a new external reference technique for calibration of microdialysis catheters in situ. This technique allows correct assessments of interstitial peptide concentrations and was employed to estimate the insulin concentration in medial quadriceps femoris muscle in 11 individuals (age: 37 +/- 3 yr; body mass index: 25.2 +/- 1.2 kg/m2) during a two-step euglycemic hyperinsulinemic clamp. At steady-state insulin and glucose infusion, plasma glucose was 5.9 +/- 0.2 mmol/l, plasma insulin was 155 +/- 17 mU/l, and interstitial muscle insulin was 67 +/- 19 mU/l (n = 9; P < 0.01). At a higher insulin infusion rate, the steady-state plasma insulin concentration was 379 +/- 58 mU/l, and interstitial insulin concentration was 180 +/- 40 mU/l (P < 0.01). The data show for the first time that high physiological and supraphysiological plasma insulin levels give 30-50% lower interstitial concentrations of insulin in the muscle. The importance of capillary delivery as a rate-limiting step for the insulin effect is suggested.

Background: To assess the relationship between systemic blood pressure, metabolic variables and adipose tissue blood flow, we studied 55 subjects before and 36 subjects after an oral glucose load (100 g)., Methods: The subjects were divided into four different groups: (a) young lean control subjects [age 31 +/- 1 years, mean +/- SE, BMI (body mass index) 22.7 +/- 0.4 kg m-2]; (b) young obese subjects (age 29 +/- 2 years, BMI 37.8 +/- 1.8 kg m-2); (c) middle-aged obese subjects (age 50 +/- 2 years, BMI 30.2 +/- 0.9 kg m-2); and (d) middle-aged obese non-insulin-dependent diabetic (NIDDM) subjects (age 54 +/- 2 years, BMI 30.0 +/- 0.7 kg m-2)., Results: Groups 2-4 demonstrated a low fasting adipose tissue blood flow (ATBF) and the increase in ATBF after oral glucose was impaired. A further impairment was present in NIDDM subjects. Systolic and diastolic blood pressure were also increased in groups 2-4 and further so in group 4. Fasting glucose, lactate and free fatty acid (FFA) levels correlated positively with the systolic blood pressure, whereas ATBF correlated negatively with the diastolic blood pressure. Furthermore, in the NIDDM subjects fasting lactate correlated closely with both the systolic (r = 0.649, P = 0.01) and diastolic (r = 0.626, P = 0.013) blood pressure., Conclusion: These data suggest a close relationship between insulin resistance and regulation of adipose tissue blood flow as well as blood pressure.

Centrally mediated sympathetic stimulation of subjects who have suffered a spinal cord injury (SCI) does not activate the decentralized part of the body below the level of the lesion, whereas experimental data indicate an exaggerated response above the level of the lesion. SCI subjects may exhibit an autonomic dysreflexia reaction following afferent stimulation below the level of the lesion. In order to investigate the function of the sympathetic nervous system above and below the level of the lesion, regional noradrenaline spillover was measured by means of steady-state isotope dilution technique above (forearm) and below (leg) the level of the lesion at baseline, during mental stress and following bladder stimulation in nine SCI subjects (mean age 41 years; level of injury C7-T4; mean duration of injury 13.8 years). The results from the SCI subjects were also compared with those from 10 weight- and age-matched control subjects, both at rest and during mental stress. Body composition was determined by dual energy X-ray absorptiometry scanning and arm/leg blood flow by occlusion plethysmography. At baseline, total and regional noradrenaline spillover did not differ between the groups. Mental stress increased mean arterial pressure in both groups. Heart rate (76 versus 64 beats/min; P < 0.05) and arm noradrenaline spillover (2.73 versus 1.71 pmol/min/100 g; P < 0.05) increased more in spinal cord injury subjects than in control subjects, whereas total body (2826 versus 3783 pmol/min; P < 0.01) and leg noradrenaline spillover (0.23 versus 0.41 pmol/min/100 g; P < 0.05) increased only in the control group. During bladder stimulation, SCI subjects reacted with a marked increase in mean arterial pressure and leg noradrenaline spillover (from 0.06 to 0.91 pmol/min/100 g; P < 0.05) and their leg blood flow decreased. Regional and total noradrenaline clearance were similar in the two groups. In conclusion, peripheral afferent stimulation below the level of the lesion in spinal cord injury subjects gives rise to a marked noradrenaline spillover from the decentralized part of the sympathetic nervous system suggesting a remaining, but qualitatively altered, neuronal function. Centrally mediated stimulation induced an exaggerated response above the level of the lesion.

Psoriatic plaques contain an increased number of mast cells. Both the histamine concentration and release are increased in lesional skin but the underlying mechanisms are unclear. One hypothesis is that neuropeptides transmitted from thin sensory cutaneous nerves continuously stimulate mast cell release of histamine. The aim of this study was to test this hypothesis by examining if topical anaesthesia of these nerves inhibits histamine release in psoriatic skin. The concentration of histamine was measured in microdialysates obtained from lesional and non-lesional skin before and during topical anaesthesia. Concomitantly skin blood flow was measured with scanning laser Doppler (perfusion) and/or 133Xe clearance (flow) techniques in the microdialysis area. The histamine concentrations (mean +/- SEM) were 34 +/- 4 (n = 21), 14 +/- 1.5 (n = 18) (P < 0. 001) and 2.8 +/- 1 nmol/L (n = 10) in lesional and non-lesional skin and plasma, respectively. After anaesthesia of the microdialysis areas the histamine concentration in psoriatic skin increased to 44 +/- 4 nmol/L (n = 19, P < 0.05), but remained unaltered in uninvolved skin. In anaesthetized lesional skin the perfusion decreased from 3.7 +/- 0.2 to 2.5 +/- 0.3 V and blood flow decreased from 14 +/- 5 to 9 +/- 1 mL/min per 100 g (P < 0.001, n = 10). The calculated release of dermal histamine in involved skin (198 +/- 30 pmol/min per 100 g, n = 10) remained unchanged after local anaesthesia. The results indicate that neurogenic activation of mast cells is of minor importance for continuous histamine release in psoriatic skin and that the vasodilatation in the psoriatic plaque is not mediated by histamine.

The psoriatic plaque contains an increased number of mast cells that are thought to have an important role in the initiation and maintenance of psoriatic lesions through the release of mediators such as histamine, proteoglycans, lipid mediators, and cytokines. It is not known, however, whether the interstitial concentration of histamine (and other mediators) is truly increased in the psoriatic plaque. The aim of the present study was to examine histamine concentration and histamine release from involved and uninvolved skin of psoriatic patients. Intracutaneous microdialysis was performed in lesional and nonlesional skin of 23 psoriatic subjects. The relative recovery of histamine was assessed after calibration in situ to approximately 76% in both lesional and nonlesional skin. The interstitial histamine concentration was 32 +/- 3 nmol per liter in lesional skin and 13 +/- 1 nmol per liter in nonlesional skin (mean +/- SEM) (p < 0.001). Dermal histamine release was estimated according to the Fick principle after measurements of the arterialized venous plasma histamine concentration (3 +/- 1 nmol per liter) and blood flow and was found to be 10-fold increased in lesional compared with nonlesional skin. The results are compatible with the hypothesis that mast cells in lesional skin secrete an increased amount of histamine that may contribute to the immunostimulation and inflammation in the psoriatic plaque.

Most neurophysiological studies have shown similar sympathetic outflow to arm and leg. However, some direct microneurographic recordings indicate differentiated sympathetic outflow to limbs both at rest and during mental stress. Hence, differentiated levels of norepinephrine (NE) spillover could prevail. By steady-state infusion of [3H]NE and body composition determination by dual-energy X-ray absorptiometry-scan, we simultaneously assessed arm and leg NE spillover related to 100 g tissue and total limb weight. NE spillover was lower in leg than arm (0.26 vs. 1.51 pmol.min-1.100 g-1, P < 0.05), and the difference remained when expressed as a function of total limb weight (66 vs. 137 pmol/min, P < 0.05). Fractional extraction of [3H]NE was similar in arm and leg. Neuronal uptake blockade by desipramine was more effective in leg than arm; fractional extraction in leg decreased by 32% (P < 0.05) but was unaltered in arm. Thus a lower NE spillover was observed from leg than arm, possibly reflecting a lower sympathetic outflow and a more neuronally dependent reuptake.

Smoking is associated with insulin resistance, dyslipidaemia and markers of the insulin resistance syndrome. This study investigated adipose tissue lipolysis in situ by subcutaneous microdialysis twice in 10 healthy, male smokers after smoking four cigarettes over 2 h and after the administration of an equal amount of nicotine given as nasal spray (NNS). Glucose and insulin levels, in situ lipolysis and adipose tissue blood flow were studied in the post-absorptive state and after a 75-g oral glucose tolerance test (OGTT). Post-absorptively, acute smoking and NNS increased neither subcutaneous adipose tissue glycerol production nor plasma free fatty acid (FFA) or glycerol levels. After the OGTT, plasma insulin and lactate levels were significantly higher after smoking, whereas FFA levels were higher after NNS. Normal smoking or the administration of a normal dose of NNS caused only minor metabolic changes. Thus, it does not seem likely that increased lipolysis is an important contributor to the dyslipidaemia seen in smokers.

To evaluate the regulation of lipolysis by the sympathetic nervous system, eight spinal cord-injured (SCI) subjects with a lesion above T5 resulting in a decentralization of the lower-body sympathetic nervous system and adrenal medulla (age, 36 +/- 2 years; weight, 82 +/- 5 kg; body fat mass, 26.8 +/- 3.0 kg; all mean +/- SE) and nine control subjects (age, 33 +/- 2; weight, 80 +/- 3; NS; body fat mass, 16.1 +/- 1.5 kg; P < .01) were investigated after fasting overnight. Each subject was studied with subcutaneous microdialysis and 133Xe-clearance adipose tissue blood flow (ATBF) in the umbilical and clavicular regions during postabsorptive rest and after sympathoexcitatory stimulation by means of mental stress and isometric handgrip exercise. SCI subjects had an increased body fat mass, hyperinsulinemia, and an elevated lipolytic rate at rest compared with control subjects. ATBF and lipolysis were activated to a normal extent following mental stress and isometric handgrip exercise in the umbilical region in control subjects. ATBF was increased in tissue above but not below the lesion level in SCI subjects following mental stress. Glycerol release was not different between groups in either tissue region despite significantly lower noradrenaline and adrenaline levels in SCI subjects. This finding argues against a significant adrenergic control of the lipolytic rate at rest. Furthermore, the small differences in stimulated glycerol release between groups, as well as the increased plasma glycerol levels in SCI subjects, cast doubt on the view that interruption of adrenergic activity below the lesion is the sole mechanism underlying the increased body fat mass in SCI subjects.

The aim of the present study was to elucidate events in the plasma membrane (PM) associated with the previously described effect of insulin to rapidly enhance the number of cell surface insulin binding sites in rat adipocytes. [125I]insulin was cross-linked to cell surface insulin receptors of intact cells that had been preincubated with or without insulin. Subsequently prepared PM displayed a approximately 3-fold increase in bound [125I]insulin when cells had been pretreated with 6 nM insulin for 20 min compared to membranes from control cells, and SDS-PAGE with autoradiography showed that this occurred at the insulin receptor alpha-subunit. The magnitude of the effect was similar to that found for insulin binding to intact cells that had been preincubated with insulin. In contrast, the insulin binding capacity in the PM was not affected by prior treatment of cells with insulin when assessed with the addition of [125I]insulin directly to solubilized PM; this suggests an unchanged total number of PM receptors. Thus, the enhancement of cell surface insulin binding capacity produced by insulin is not due to the translocation of receptors, but instead appears to be confined to receptors already present in the PM. The addition of phospholipase C (from Clostridium perfringens), which cleaves PM phospholipids, mimicked the effect of insulin to enhance cell surface binding in adipocytes, and this suggests a pool of cryptic PM receptors. Both the nonmetabolizable cAMP analog N6-monobutyryl cAMP (N6-mbcAMP) and the serine/threonine phosphatase inhibitor okadaic acid abolished the effect of concomitant insulin treatment to increase binding capacity. In contrast, the tyrosine phosphatase inhibitor vanadate increased insulin binding even in the presence of okadaic acid or N6-mbcAMP. The effect of N6-mbcAMP to impair cell surface insulin binding was also evident in the presence of a peptide derived from the major histocompatibility complex type I that effectively impairs receptor internalization, but the amount of PM receptors assessed by immunoblot was unaltered. Taken together, the data suggest that insulin exposure leads to the uncovering of cryptic receptors associated with the PM. It is also suggested that tyrosine phosphorylation promotes this process, whereas enhanced serine phosphorylation, e.g. produced by cAMP, impairs the functional insertion of the receptors, rendering them unable to bind insulin.

The aim of the present study was to examine the effects of a large dose of slow-release carbohydrates (CHOs) at bedtime on the nocturnal glucose, insulin and free fatty acid (FFA) levels, and to assess the putative effects on morning fasting and post-prandial glucose levels in patients with moderately controlled non-insulin-dependent diabetes mellitus (NIDDM). Unheated cornstarch (106 g of CHO) or a mixed equicaloric meal (58 g of CHO) was given at 22.00 hours to 10 NIDDM patients. For comparison, the patients were also given a smaller mixed meal at 22.00 hours on a third occasion (17 g of CHO). Compared with the mixed meals, cornstarch led to a slightly elevated early-morning plasma insulin level and a suppression of the nocturnal FFA level (P < 0.05), as well as to a reduced incremental glucose level (IAUC) after breakfast the next morning by approximately 30% (P < 0.05). There was a significant and linear relationship between the nocturnal FFA level and the glucose IAUC after breakfast (r = 0.44, P < 0.02), indicating that the effect may have been mediated by the suppressive effect of cornstarch on nocturnal lipolysis. In summary, bedtime intake of unheated cornstarch in NIDDM subjects is associated with a suppression of the nocturnal FFA levels and a reduced glucose IAUC after breakfast. As the treatment did not improve overall glucose control, studies of the effects of an individually titrated amount of cornstarch are proposed to further explore the putative favourable effects of bedtime cornstarch in the treatment of NIDDM.

To evaluate the effect of metoprolol on insulin sensitivity and diurnal plasma hormone levels, seven mildly hypertensive subjects were investigated (four men and three women, age 52 +/- 8, body mass index 25.4 +.- 1.9, mean +/- SD). The study had a placebo-controlled, double-blind, crossover design with 6 weeks' metoprolol treatment (100 mg b.i.d) vs. placebo. At the end of each treatment period 24-h blood samples were collected continuously for diurnal analysis of hormone levels and a hyperinsulinaemic euglycaemic clamp combined with [3-3H]-D-glucose infusion was performed. Insulin sensitivity was evaluated by means of three different methods: diurnal plasma insulin and glucose levels; glucose consumption; and insulin sensitivity index during euglycaemic clamp conditions. Fasting blood glucose and insulin concentrations as well as mean plasma diurnal levels of insulin, growth hormone, testosterone and cortisol were similar after placebo and metoprolol treatment, whereas noradrenaline and adrenaline levels were significantly increased after metoprolol. During the clamp, plasma insulin was significantly higher after metoprolol treatment than after placebo treatment (56 +/- 3 vs. 64 +/- 2 mU L(-1), P < 0.05). Consequently, the insulin sensitivity index [glucose infusion rate (GIR)/ plasma insulin] was lower after metoprolol treatment (16.1 +/- 2.6 vs. 10.2 +/- 1.2, P < 0.05), although GIR was not significantly changed. We suggest that the insulin sensitivity index may not accurately reflect the insulin effect as the plasma level of insulin was significantly increased during insulin infusion but not at 24 h, possibly because of alteration of distribution and/or degradation rate of exogenous insulin. Thus, the likelihood of metoprolol inducing insulin resistance in hypertensive subjects may be less than previously proposed.

To study the relationship between blood flow rate and muscle metabolism, muscle microdialysis was performed in nine human subjects (5 females and 4 males) after an oral glucose load (75 g). Two microdialysis probes were inserted into the medial femoral muscle for estimation of glucose and lactate concentrations in the interstitial fluid, and the muscle blood flow was measured concomitantly with strain-gauge plethysmography. After subjects fasted overnight, their glucose concentration in arterial plasma and interstitial fluid was 4.6 +/- 0.13 vs. 3.8 +/- 0.23 mmol/l (P < 0.05), and the corresponding lactate concentrations were 0.60 +/- 0.07 vs. 0.83 +/- 0.07 mmol/l (P < 0.05). Muscle blood flow was 5.2 +/- 0.7 and 7.5 +/- 1.4 ml.100 g-1.min-1 (P < 0.05) at 0 and 90 min after oral glucose, respectively. The arterial-interstitial concentration differences of glucose increased after oral glucose [at 0 min 0.73 +/- 0.24 vs. 2.19 +/- 0.60 mmol/l at 90 min (P < 0.001)]. The corresponding values for lactate were -0.23 +/- 0.10 at 0 min vs.-0.26 +/- 0.18 mmol/l at 90 min (not significant). The data show that 1) the capillary wall is partly rate limiting for glucose uptake, and 2) after oral glucose, the glucose concentration gradient over the capillary wall increases despite a limited increase in blood flow rate, which then mediates approximately 10-20% of total enhancement of glucose uptake in muscle.

Objective: To characterize differences in metabolic indices as well as body composition in two ethnic groups., Subjects: Eight black and eight white obese urban women were studied., Design: Eight black and eight white obse (BMI > 34) urban women (BW, WW) were matched for age, BMI, WHR, diet and physical activity and investigated before and after 12 weeks of Dexfenfluramine treatment., Measurements: Anthropometric measurements; Post 75 g OGTT, plasma glucose, insulin and C-peptide levels were done. FFA and lactate levels were done at onset. Skinfold thickness with Harpenden calipers, bio-impedance for analyses of body composition and CT scan for assessment of regional adiposity (at onset and after 3 months)., Results: In the postabsorptive state the WW had significantly higher plasma total cholesterol and triglyceride levels and an unfavourable HDL : total cholesterol ratio. Their FFA levels were significantly lower (324 +/- 51 vs 985 +/- 84 mumol/l; p < 0.0001) and their lactate levels were significantly higher (3045 +/- 245 vs 1938 +/- 358 mumol/l; p < 0.001) as compared with the BW. During a 75 g OGTT the BW had significantly higher glucose levels at 1 h (8.6 +/- 0.8 vs 5.1 +/- 0.4 mmol/l; p < 0.005) and 2 h (7.6 +/- 0.6 vs 4.4 +/- 0.3 mmol/l) but not at fasting. In contrast the BW had lower insulin concentrations (fasting: 77 +/- 9 vs 139 +/- 19 pmol/l; p < 0.04 and 1 h 318 +/- 56 vs 624 +/- 75 pmol/l; p < 0.005), and C-peptide concentrations (fasting: 400 +/- 99 vs 1600 +/- 99 pmol/l; p < 0.000 04, 1 h 1400 +/- 433 vs 5966 +/- 333 pmol/l; p < 0.0007 and 2 h 1266 +/- 333 vs 4066 +/- 366 pmol/l; p < 0.0005). CT scan measurements showed that the WW had significantly more visceral fat than the BW (148.5 +/- 2.0 vs 115.5 +/- 6.9 cm2; p < 0.05) but lost less weight during Dexfenfluramine treatment (-4 kg vs -9 kg). Despite this, the WW lost more visceral fat than the BW (-27.3 cm2/-18.5%; p < 0.03 vs -15.5 cm2/-13.2%; p < 0.04). In contrast the BW had a larger reduction in subcutaneous (SC) fat (-13.9% vs -1.7%; p < 0.01), with the greatest reduction in the SC gluteofemoral adipose tissue (widest hip circumference -20.8% vs -0.2%; p < 0.001) and mid-femur region (-13.1% vs -0.7%; p < 0.08)., Conclusion: Weight loss in obese black women is associated with a major reduction in SC fat mass with the most active mobilization of fat tissue occurring in the gluteofemoral area. In contrast the WW had more visceral fat that was more readily mobilized. The difference in adipose tissue distribution and pattern of mobilization was associated with lower plasma insulin, C-peptide and triglyceride concentrations in the BW despite increased FFA and glucose levels. These data suggest that plasma insulin concentrations are important in regulating differences in regional adipose tissue metabolism as well as the serum lipid profile.

To assess net lactate release from dermal skin, seven lean, healthy men were studied after overnight fasting. Two microdialysis catheters were inserted in the upper dermal tissue, as ensured by ultrasound scanning, in the periumbilical area. Each catheter was calibrated in situ to get an estimate of the lactate concentration in interstitial fluid (1,001 +/- 24 mumol/l), which in turn enabled calculation of the local capillary-venous lactate concentration (963 +/- 25 mumol/l). Concomitantly, arterialized venous plasma lactate (673 +/- 32 mumol/l), blood hematocrit (43 +/- 1%), and skin blood flow (3.8 +/- 0.9 ml.100 g-1.min-1) as measured by 133Xe clearance were determined, and dermal apparent lactate release (570 +/- 89 nmol.100 g-1.min-1) was estimated according to the Fick principle. During an oral glucose tolerance test (OGTT, 75 g), the dermal interstitial-arterial lactate difference decreased significantly to reach a nadir at 60 min. Moreover, no significant increase in skin blood flow was seen during the OGTT. In conclusion, we found a significant net lactate release from abdominal dermal skin after overnight fasting, whereas no significant increase was observed during an OGTT.

In this study we aimed to validate the microdialysis technique for metabolic measurements in the dermal interstitial fluid. The abdominal and forearm skin was used for microdialysis in 15 healthy normal weight volunteers. The depth of the microdialysis catheter was assessed by ultrasound measurement. Structural impairment and blood flow were judged from biopsies and from laser Doppler measurements taken adjacent to the catheters. Dermal interstitial lactate and pyruvate concentrations were measured, under steady state fasting conditions, after equilibrium calibration of each catheter in situ. The dermal interstitial glucose concentration was estimated by means of the retrodialysis calibration method, which has previously not been evaluated for skin microdialysis. The mean catheter depth (+/- standard deviation) was 0.8 +/- 0.3 mm. Small areas of localized bleeding, but no inflammatory reaction, was found surrounding the catheters. The perfusion in the microdialysis region was slightly increased (15-25%). The lactate/pyruvate ratio (12 +/- 0.7) showed non-ischaemic values. The dermal interstitial lactate concentration was significantly higher (1171 +/- 228 mumol/l) than the plasma lactate (781 +/- 180 mumol/l), indicating an ongoing nonoxidative glucose metabolism. Retrodialysis calibration correctly estimated the dermal glucose level to be similar to that in plasma, which may indicate the usefulness of this calibration method for microdialysis studies of endogenous substrates in the dermal interstitial fluid.

The importance of increased capillary density for the regulation of insulin sensitivity by transcapillary delivery of insulin to muscle cells in insulin-exposed rats was investigated by direct microdialysis measurements of interstitial (125I] insulin concentrations in the femoral muscle during an euglycaemic hyperinsulinaemic clamp. In insulin-exposed rats plasma insulin was approximately 25% (P < 0.05) higher than that in control animals during the first 100 min and reached their maximal concentrations after 100 min. After a nitroprusside infusion given at 100 min both groups had similar concentrations of insulin in plasma as well as in muscle interstitial fluid. However, mean glucose infusion rate during the first clamp hour was 20.5 +/- 2.3 and 12.6 +/- 5.2 mg kg-1 min-1 (P < 0.05) in insulin-exposed and control animals, respectively. During the second clamp hour the corresponding figures were 21.1 +/- 2.4 and 13.9 +/- 2.6 (P < 0.05). It may be concluded that capillarization and/or nitroprusside affected plasma insulin concentrations without altering either the interstitial insulin levels or the insulin effect on glucose consumption. The data suggest that the elevated insulin sensitivity after chronic insulin exposure is dependent on other than transcapillary transport events and demonstrate the different kinetics for insulin distribution in plasma and in the interstitial fluid.

Objective: To examine the effect of metformin on net lactate and glycerol release in NIDDM subjects, we used abdominal subcutaneous microdialysis combined with 133Xe clearance. Skeletal muscle blood flow (MBF) was assessed simultaneously both before and after metformin treatment., Research Design and Methods: Nine male patients with NIDDM (age 53 +/- 2 years [mean +/- SE]; BMI 30.2 +/- 1.4 kg/m2; body fat 23.0 +/- 2.6 kg; diabetes duration 4.6 +/- 1.5 years; six of nine receiving sulfonylurea treatment) were recruited into an open study. They were studied after an overnight fast, both before and after 1 week of additional treatment with 500 mg metformin three times daily. Nine weight- and age-matched nondiabetic subjects served as a control group., Results: Postabsorptive net subcutaneous lactate release increased (149 +/- 50 vs. 475 +/- 127 nmol.100 g-1.min-1, P < 0.05) whereas plasma lactate was unchanged after metformin treatment in the NIDDM patients. The net decrease of glycerol release 90 min after an oral glucose tolerance test was more pronounced (110 +/- 30 vs. 199 +/- 20 nmol.100 g-1.min-1, P < 0.05) after metformin treatment. Both adipose tissue blood flow (ATBF) (1.5 +/- 0.1 vs. 2.3 +/- 0.2 ml.100 g-1.min-1, P < 0.01) and MBF (3.2 +/- 0.4 vs. 4.2 +/- 0.5 ml.100 ml-1.min-1, P < 0.05) increased after metformin treatment., Conclusions: In this open study, postabsorptive net lactate release in abdominal subcutaneous adipose tissue was clearly increased in NIDDM patients after metformin treatment. Basal ATBF as well as MBF was improved after metformin treatment. Whether this reflects enhanced metabolic control or is a drug-specific effect remains to be established.

To evaluate insulin sensitivity and adipose tissue metabolism, seven spinal cord-injured (SCI) subjects (age, 43 +/- 6 years; body mass index, 22.8 +/- 1.4; mean +/- SE) and their seven siblings (age, 45 +/- 6 years; body mass index, 24.8 +/- 0.8) were studied using oral glucose (100-g) tolerance tests (OGTTs), euglycemic insulin clamps (insulin infusion, 1 mU/kg.min), and microdialysis of the subcutaneous tissue. Blood glucose and insulin after oral glucose were significantly increased in SCI subjects as compared with their siblings. During insulin clamping, plasma adrenaline increased significantly in controls, but not in SCI subjects. However, the rates of glucose production (2.02 +/- 0.36 v 1.59 +/- 0.09 mg/kg.min) and utilization (5.13 +/- 0.71 v 5.78 +/- 0.34) were similar in the two groups. Furthermore, interstitial subcutaneous glycerol and lactate concentrations before and after oral glucose were similar in the two groups, even in neurally decentralized tissue with broken connection between the central nervous system and peripheral sympathetic nerves. The data suggest that (1) well-mobilized SCI subjects show minor insulin resistance, and (2) sympathetic nervous activity has a minor influence on adipose tissue metabolism in the postabsorptive state, but may affect insulin sensitivity during euglycemic clamping.

A microdialysis technique has been developed for estimation of concentrations of low molecular size compounds in the interstitial fluid in vivo. With this technique urea kinetics in the interstitial fluid and plasma were studied in ten patients during and after hemodialysis. There was a close correspondence between urea measurements in plasma and interstitium during hemodialysis. Urea rebound occurred in plasma during two hours after dialysis (15.8 +/- 6.5% in the first hour and 11.8 +/- 5.9% in the second hour). The urea rebound in the interstitium was delayed about 60 minutes after that of plasma (2.8 +/- 8% and 14.1 +/- 7.8% in the first and second hours, respectively) and continued for up to four hours after dialysis. The relationship between plasma urea rebound and the efficiency of hemodialysis and ultrafiltration volume was studied in 17 patients. Results showed a close relation between the fractional urea removal during dialysis and the plasma urea rebound. The contribution of de novo urea genesis to the rebound was estimated from the interdialytic increase in plasma urea concentrations, and was 17 to 24% of the plasma urea rebound during two hours postdialysis. The initial plasma urea rebound could in part result from urea influx to plasma from the enterohepatic recirculation of urea nitrogen. Plasma urea rebound should be taken into account for determination of the amount of dialysis delivered during hemodialysis.

To investigate the mechanisms by which amiloride inhibits insulin action rat adipocytes were treated with insulin and with amiloride added before or after energy depleting the cells with 2 mM KCN. Amiloride decreased the insulin response on 3-0-methylglucose transport, IGF-II- and insulin binding in both intact and energy depleted cells. In contrast, the sensitivity to insulin was inhibited by amiloride only when it was added before KCN. The effect of amiloride on insulin sensitivity was probably exerted through the impaired activation of the insulin receptor tyrosine kinase and the decreased insulin binding. However, insulin responsiveness was probably impaired through a direct effect on the plasma membrane proteins. In contrast to a recent report with pituitary cells, amiloride did not affect the activation of the inhibitory GTP-binding protein (Gi) in rat adipocytes.

Insulin regulates cellular metabolic reactions by its action on the plasma membrane, intracellular enzymes and the nucleus. The first stage in the propagation of the insulin signal is the coupling of insulin to specific receptors at the cell surface. The exact mechanism whereby the transmembrane signalling mechanism (s) results in different insulin-mediated cellular effects is not known. However, the insulin receptor tyrosine kinase, the expression of second messengers, and the action of protein kinase C may, either individually or in combination, mediate some of the insulin effects, such as translocation and activation of glucose transporter proteins. Insulin resistance in clinical conditions such as insulin-dependent diabetes mellitus (IDDM), non-insulin-dependent diabetes mellitus (NIDDM), hypertension and obesity may be acquired to a large extent, and is thus partially reversible. Regulatory factors in insulin sensitivity, such as free fatty acids, counterregulatory hormones and blood glucose level, play an important role in the metabolic control and pathogenesis of insulin resistance in man.

Interstitial glycerol concentrations were measured in the abdominal and femoral subcutaneous tissue in 10 lean and 6 obese subjects. In the lean subjects [waist-hip circumference ratio (WHR) 0.89 +/- 0.01] the fasting interstitial glycerol concentrations in the abdominal and femoral regions were 185 +/- 20 and 160 +/- 15 (SE) microM, respectively, whereas glycerol in venous plasma was considerably lower (66 +/- 5 microM). After an oral glucose load (100 g) the interstitial glycerol concentrations declined but remained higher than in plasma. In obese subjects (WHR 1.1 +/- 0.03) the fasting interstitial glycerol levels were higher, in both regions, than in lean individuals. Furthermore, interstitial glycerol in the abdominal site (291 +/- 32 microM) was significantly higher than in the femoral fat (210 +/- 13 microM; P less than 0.05), while plasma glycerol was similar to that in lean subjects (80 +/- 12 microM). Interstitial glycerol remained higher in the obese than in the lean subjects also after an oral glucose load, but the regional differences were less apparent. Thus interstitial glycerol is higher in the subcutaneous tissue than in venous blood. The data also suggest that lipolysis is enhanced in the abdominal subcutaneous tissue as compared with the femoral site in obese subjects and that lipolysis is exaggerated in both regions in obese as compared with lean individuals.

The metabolism of subcutaneous abdominal and femoral fat cells was studied in postmenopausal women and matched men of similar age and weight index. Lipoprotein lipase (LPL) activity was similar in both regions in the postmenopausal women. However, a group of women who underwent treatment with estrogen and progestins had considerably higher LPL activity in the femoral cells. Testosterone treatment for 7 days did not change LPL in either region in middle-aged men. Femoral adipocytes from both men and postmenopausal women were markedly unresponsive to catecholamine in comparison with abdominal cells. No clear effect of the sex hormones was seen on lipolysis in the women. Treating men with testosterone increased basal lipolysis in the abdominal cells. Abdominal fat cells were more responsive to the antilipolytic effect of insulin. Both responsiveness and sensitivity to insulin were somewhat greater in the abdominal fat cells from men (ED50 approximately 0.02 nm) than from women (ED50 approximately 0.17 nm). Insulin binding, however, was similar in fat cells from the abdominal and the femoral regions when the results were expressed per unit surface area. Thus, regional differences in fat cell metabolism are seen in both postmenopausal women and elderly men. LPL activity in the femoral region seems to be under the control of female sex hormones while lipolysis appears to be less influenced by sex hormones.

Insulin responsiveness was studied with the euglycaemic glucose clamp technique in seven patients with type I diabetes and in six control subjects matched for age and weight. The glucose disposal rate was significantly reduced in the diabetic subjects when they were receiving conventional insulin treatment compared with the control group, showing insulin resistance in the diabetics. The diabetic patients were again studied after eight days of intensified metabolic control achieved with continuous subcutaneous insulin infusion. During the infusion a more physiological insulin regimen was used compared with their regular treatment, less of the total insulin dose being given as continuous infusion and more as bolus doses before meals. The insulin resistance in the diabetics was largely reversed after this improved metabolic control. Dose response studies showed an increased glucose disposal rate at all plasma insulin concentrations, including the maximum insulin concentration, indicating a predominant effect of the continuous infusion regimen at the postreceptor level. The improved insulin effect seen with continuous subcutaneous insulin infusion could be due to the improved metabolic control achieved as well as the more physiological regimen.

Hypoglycemic attack rate, duration and symptomatology were studied in five insulin-dependent diabetics with borderline hypertension all of whom were prone to hypoglycemia. They were treated in a double-blind, cross-over fashion with the cardioselective beta 1-blocking agent metoprolol and placebo. The treatment period on each drug lasted at least three months. No treatment-associated differences in attack rate and duration of hypoglycemic attacks were recorded. Slight, but no severe masking of hypoglycemic symptoms was recorded in one patient on metoprolol. It is concluded that cardioselective beta 1-blocking agents can be used by insulin-dependent diabetics. However, until further direct experience has been gained caution should be exercised in treating patients with obvious clinical signs of autonomic neuropathy with these drugs.

Bacitracin (1 mg/ml) markedly increased (approx. 75%) the cell-associated specifically bound 125I-labelled insulin without altering the affinity of the binding sites. Bacitracin also exerted a modest inhibitory effect on the degradation of insulin in the incubation medium determined as radioactivity not precipitated by trichloroacetic acid (from 9.6 to 4.8%). The effect on insulin binding was about 5-times as sensitive as the effect on degradation. The increased binding was due to intracellular accumulation of radioactivity which could not be removed by treating the cells with trypsin. This increase was not seen when the internalization process was reduced by ATP-depletion or low temperature. Since the trypsin-sensitive fraction of cell-associated radioactivity was apparently not altered, it is suggested that bacitracin, in addition to its well-known inhibition of extracellular degradation, also inhibits the intracellular degradation of insulin.

Human fat cells were incubated with two different cAMP analogues, 8-bromocAMP and 6N-monobutyrylcAMP. The former analogue is an excellent substrate for the phosphodiesterase while the latter is resistant to hydrolysis. In the presence of adenosine deaminase, isoproterenol (10(-6)M) stimulated lipolysis 8-10 fold which was similar to the effect exerted by the cAMP analogues. Basal lipolysis and lipolysis activated by 6N-monobutyrylcAMP was not inhibited by insulin even at high concentrations, whereas the effect of 8-bromocAMP was virtually completely inhibited. This effect of insulin was completely prevented by the addition of IBMX. Thus, activation of phosphodiesterase by insulin is necessary to elicit the antilipolytic effect in human adipocytes.

In order to study factors regulating insulin binding to rat adipocytes short- and long-term incubations were performed in the presence or absence of noradrenaline (NA) at a concentration of 3 microM. Culture with NA for 24 hours resulted in a significant decrease (30%) of insulin binding due to a reduced number of binding sites. This reduction was dose-dependent and completely prevented by the addition of timolol, a beta-adrenergic blocking agent, but not by the alpha-blocking agent phentolamine. Addition of 1.0 mM db cAMP to the culture medium resulted in a similar reduction in insulin binding. Also short-term incubations with NA resulted in a downregulation of insulin binding; reproducible reductions seen already after 20 min and about 30% reduction achieved after 2 hours' preincubation. Thus, beta-adrenergic stimulation and subsequent cAMP elevation results in a rapid reduction in the number of insulin binding sites.

Insulin resistance is evident in several clinical conditions such as obesity, diabetes type II, hypercortisolism. The mechanisms behind this resistance at the level of the target cell can be evaluated with measurements of insulin sensitivity with techniques both in vitro and in vivo. In this review various techniques used to evaluate insulin action are discussed and also some clinical conditions associated with insulin resistance.