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S Matthaei

Publications and source records attributed to S Matthaei.

At least 37 records · Page 2Linked to original sources
PubMed1997

Chronic leptin treatment does not prevent the development of obesity in transgenic mice with brown fat deficiency.

With the exception of ob/ob mice, circulating plasma leptin is elevated in all other obese rodents as well as in obese humans, suggesting that leptin resistance rather than leptin deficiency is a characteristic feature of obesity. The exact molecular mechanisms leading to leptin resistance and the applicability of exogenous leptin to overcome resistance to the anorectic effect of the hormone, are insufficiently characterized. The aim of this study was to investigate whether chronic leptin administration could prevent the development of obesity and its associated disorders in transgenic mice with toxigene mediated ablation of brown adipose tissue (BAT). Daily injections of leptin were started at the age of 6 weeks, when body weight, food intake and plasma leptin levels of transgenics were not different from control mice. Over the next 6 weeks, leptin treated transgenics showed the same excessive body weight gain as transgenic mice injected with saline. Leptin treatment was furthermore not able to prevent the development of hyperphagia, hyperglycaemia, hyperinsulinaemia and hyperlipidaemia in transgenic mice. In contrast, control mice injected with leptin had significantly lower body weight, food intake and plasma triglycerides than those treated with saline. In summary, leptin treatment was not able to prevent the development of obesity and its associated abnormalities in transgenic mice with BAT deficiency. This data suggests that intact BAT function is of critical importance for leptin's effect on food intake and energy expenditure, and that primary dysfunction of BAT is associated with leptin resistance, even when hyperleptinaemia is not yet present.

Adipose Tissue, Brown↗
PubMed1996

Regulation of energy balance by leptin.

The high prevalence of obesity and its well documented association with the cardiovascular risk factors diabetes mellitus, dyslipidemia and hypertension represents a major problem for the general health status of industrialized societies. Although numerous studies have shown that genetic factors have a major influence on the regulation of energy homeostasis and the susceptibility to obesity, the genes and predisposing mutations involved are insufficiently understood. Among several known rodent models of obesity due to single gene mutations, mice homozygous for the obese (ob) gene exhibit massive early-onset obesity, hyperphagia, non-insulin-dependent diabetes mellitus, defective thermoregulation and infertility. Recently the ob gene was identified by positional cloning and shown to be mutated in ob/ob mice. Leptin, the product of the ob gene, is a 167-amino acid secreted protein that is synthesized exclusively in adipose tissue. With the exception of ob/ob mice, circulating plasma leptin is elevated in obesity. Administration of recombinant leptin to ob/ob mice reduces fat mass, food intake, hyperglycemia and hyperinsulinemia. The various effects of the hormone are mediated by leptin receptors expressed at high levels in the hypothalamus, but also in several other non-neuronal tissues. A mutation in the leptin receptor gene is responsible for the obese phenotype of db/db mice. Plasma leptin in humans is positively correlated with body fat mass, suggesting that leptin resistance rather than leptin deficiency is a common feature of human obesity. This review briefly summarizes the current status of the rapidly growing evidence that leptin plays an important role in the regulation of body weight and fat deposition.

Adipocytes↗
PubMed1995

Effect of in vivo thyroid hormone status on insulin signalling and GLUT1 and GLUT4 glucose transport systems in rat adipocytes.

To examine the effect of thyroid hormone status on insulin action in isolated rat adipocytes, age- and weight-matched Sprague-Dawley rats were rendered hypothyroid (h) by i.p. injection of 2 mCi [131I]/kg. Another group of rats was made hyperthyroid (H) by i.p. injection of 500 micrograms L-thyroxine/kg/day for 7 days. The T4 levels in experimental groups were: controls, 33.5 +/- 0.95; h, 12.3 +/- 1.59; H, 133.2 +/- 8.8 micrograms/l. Adipocytes were isolated and 3-O-methylglucose transport (GT), insulin binding (IB) and insulin receptor kinase activity (IRKA) were determined. Subcellular membrane fractions (low-density microsomes, plasma membranes) were prepared and GLUT1 and GLUT4 glucose transporter immunodetected. Hyperthyroidism caused no significant effect on either IB or IRKA but increased insulin-stimulated GT by 43.6%. This increase of GT was associated with an increase of primarily GLUT4 glucose transporters. Hypothyroidism was associated with both increased insulin receptor affinity and enhanced IRKA. Despite a marked reduction of primarily GLUT4 glucose transporters, basal and insulin-stimulated GT was not reduced when compared with control. These results suggest that (1) in hyperthyroidism, increased insulin-stimulated glucose transport is associated with an increase of primarily GLUT4 glucose transporters, which may be responsible for the increment of peripheral glucose utilization in hyperthyroidism, and (2) the effect of hypothyroidism on insulin action in adipocytes is characterized by a state of increased insulin sensitivity, as indicated by the increase in insulin receptor affinity and tyrosine kinase activity. Despite the marked reduction of primarily GLUT4 glucose transporters, insulin-stimulated glucose transport is not diminished, which may suggest that functional activity of plasma membrane glucose transporters is enhanced in hypothyroidism.

Adipose Tissue↗
PubMed1993

Metformin increases glucose transporter protein and gene expression in human fibroblasts.

To investigate the effect of the antihyperglycemic drug metformin on glucose transporter protein and gene expression, skin fibroblasts obtained from normal and diabetic volunteers were grown in culture and incubated with metformin at various concentration for up to 16 days. Metformin caused a dose and time dependent increase in GLUT1 number with a maximum at a concentration of 10 micrograms metformin given over 4 days. This was accompanied by an increase in GLUT1 mRNA, suggesting that metformin has a stimulating effect on glucose transporter gene expression. No significant difference was observed between cells obtained from type II diabetic patients and those from controls. We conclude that in human fibroblasts GLUT1 de novo synthesis is involved in the long term effect of metformin on glucose transport.

Adult↗
PubMed1993

Oxygen consumption and resting metabolic rate in sepsis, sepsis syndrome, and septic shock.

OBJECTIVE: To test the hypothesis that variations in oxygen consumption (VO2) and resting metabolic rate reflect the severity of bacterial infections and reflect the development of sepsis syndrome and septic shock. DESIGN: Observational study with sequential measurements of VO2 and resting metabolic rate by expiratory gas analysis. SETTING: Medical intensive care unit. PATIENTS: Thirty patients, treated primarily for presumed bacterial infection, were examined on 118 treatment days. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: VO2 and resting metabolic rate were measured by expiratory gas analysis. For mechanically ventilated patients, a measurement system was developed, based on a paramagnetic oxygen sensor, an infrared CO2 sensor, and digital signal averaging. Measurements in spontaneously breathing patients were performed with a metabolic monitor. Patients were assigned by clinical criteria to the following groups: sepsis, sepsis syndrome, and septic shock. The lowest VO2 value of each patient in each stage was evaluated. Mean VO2 in 15 patients with sepsis was 180 +/- 19 (SD) mL/min/m2, in 11 patients with sepsis syndrome 156 +/- 22 mL/min/m2, and in eight patients with septic shock 120 +/- 27 mL/min/m2 (p < .001). Mean resting metabolic rate in sepsis was +55 +/- 14%, in sepsis syndrome +24 +/- 12%, and in septic shock +2 +/- 24% (p < .001). Mean oxygen delivery (DO2) was 501 +/- 116 mL/min/m2 in sepsis, 515 +/- 186 mL/min/m2 in sepsis syndrome, and 404 +/- 96 mL/min/m2 in septic shock. Oxygen extraction (VO2/DO2) was highest in sepsis (0.39 vs. 0.33 in sepsis syndrome and 0.29 in septic shock). During recovery from sepsis syndrome or septic shock, a significant increase in resting metabolic rate to +61 +/- 22% was measured in nine patients. CONCLUSIONS: In sepsis syndrome, VO2 and resting metabolic rate are enhanced by 30% compared with normal basal metabolism, but they are markedly reduced compared with uncomplicated sepsis. The higher VO2 in uncomplicated sepsis is flow independent. The noninvasive measurement of VO2 and resting metabolic rate by expiratory gas analysis therefore can be used as a quantitative staging and monitoring parameter for the development of sepsis syndrome and septic shock.

Adult↗
PubMed1993

In vivo metformin treatment ameliorates insulin resistance: evidence for potentiation of insulin-induced translocation and increased functional activity of glucose transporters in obese (fa/fa) Zucker rat adipocytes.

To examine the cellular mechanism of the antihyperglycemic action of in vivo metformin (M) we used an animal model of severe insulin resistance, the genetically obese (fa/fa) Zucker rat. The animals were treated with or without M (250 mg/kg.day) which was supplied with the drinking water. Three weeks of in vivo M-treatment had no effect on body weight and several blood lipid parameters, but markedly reduced plasma insulin levels by 45% (-M: 2932 +/- 166 vs. +M: 1614 +/- 85 pmol/liter, P < 0.01); plasma glucose was slightly but significantly decreased by 8.3% (-M: 7.2 +/- 0.2 vs. +M: 6.6 +/- 0.16 mmol/liter, P < 0.05). Adipocytes were isolated and incubated with or without insulin. In vivo M-treatment had no effect on basal 3-O-methylglucose uptake. In contrast, in vivo M-treatment increased insulin-stimulated glucose transport by 2.6 +/- 0.6-fold (P < 0.01). Measurement of cell surface insulin receptors revealed no effect of M on neither specific [125I]insulin binding nor on insulin receptor kinase activity. Insulin-mediated translocation of both GLUT1 and GLUT4 glucose transporters was enhanced by in vivo M-treatment, GLUT1 by 26.1%, GLUT4 by 30.5%. To fully account for the M-induced increment of insulin-stimulated glucose transport (2.6-fold), these data suggest that M increased the functional activity of glucose transporters. We conclude that amelioration of insulin resistance in (fa/fa) Zucker rats after 3 weeks of in vivo M-treatment is associated with 1) a marked reduction of in vivo hyperinsulinemia, 2) an increase of insulin-stimulated glucose transport in adipocytes; 3) this increase of insulin-stimulated glucose transport is accompanied with both a potentiation of insulin-induced translocation of GLUT1 and GLUT4 glucose transporters from an intracellular pool to the plasma membrane as well as increased functional activity of plasma membrane glucose transporters. 4) This M-effect seems to be independent of de novo glucose transporter synthesis, since total cellular GLUT1 and GLUT4 glucose transporter number were uneffected by M. 5) These results strongly suggest a direct action of M at the level of glucose transport, since neither tracer insulin binding nor insulin receptor kinase activity were significantly altered by M.

3-O-Methylglucose↗
PubMed1993

A microtiter well assay system to measure insulin activation of insulin receptor kinase in intact human mononuclear cells. Decreased insulin effect in cells from patients with NIDDM.

A sensitive microtiter well-based assay for the measurement of insulin activation of insulin receptor kinase in intact human circulating mononuclear cells has been developed and characterized. Mononuclear cells from 100-150 ml blood were incubated with various insulin concentrations to activate the receptor kinase. The cells were then solubilized in the presence of phosphatase and kinase inhibitors and the receptors immobilized to microwells coated with anti-insulin receptor antibody (efficiency of receptor immobilization > 85%). Receptor kinase activity and binding activity were then consecutively measured in the same wells. Insulin incubation of the cells increased the kinase activity three- to fourfold with a half-maximal effect at 5 nM and a maximal effect at 87 nM. In mononuclear cells from 16 subjects with NIDDM, the insulin effect on receptor kinase activation was significantly reduced compared with 16 nondiabetic control subjects (0.135 +/- 0.016 vs. 0.195 +/- 0.024 fmol P.fmol binding activity-1 x min-1, respectively; P < 0.05). We conclude that; 1) it is possible to determine insulin activation of receptor kinase in intact cells in this easily accessible human tissue; 2) insulin activation of insulin receptor kinase is impaired in intact mononuclear cells from patients with NIDDM; and 3) the finding that kinase activation in NIDDM is reduced in a tissue that, according to the literature, contains only the A isoform of the insulin receptor, suggests that mechanisms other than a different abundance of the A and B insulin receptor isoforms must exist that contribute to the decreased kinase activity in NIDDM.

Aged↗
PubMed1992

Evidence that metformin increases insulin-stimulated glucose transport by potentiating insulin-induced translocation of glucose transporters from an intracellular pool to the cell surface in rat adipocytes.

To examine the cellular mechanism of the antihyperglycemic action of metformin (M) we studied the effect of M on various functional and molecular parameters involved in the pathogenesis of insulin resistance. Isolated rat adipocytes were incubated with or without M (1-100 micrograms/ml) for 2 hours at 37 degrees C followed by an incubation with or without insulin (I) (10) ng/ml). M-treatment had no significant effect on basal (B) 3-O-methylglucose uptake. In contrast, M increased I-stimulated glucose transport in a dose dependent manner up to 43 +/- 7%. This effect was neither associated with a significant effect of M on trace insulin binding, 1.74 +/- .2% (-M) vs 1.89 +/- .3% (+M), p > 0.05, nor with an effect of M on in vivo activation of insulin receptor kinase activity as measured by 32P-incorporation into the 95 kDa beta-subunit of the insulin receptor and an exogenous substrate, histone 2B.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗
PubMed1991

The relationship between insulin binding, insulin activation of insulin-receptor tyrosine kinase, and insulin stimulation of glucose uptake in isolated rat adipocytes. Effects of isoprenaline.

We have studied the relationship between insulin activation of insulin-receptor kinase and insulin stimulation of glucose uptake in isolated rat adipocytes. Glucose uptake was half-maximally or maximally stimulated, respectively, when only 4% or 14% of the maximal kinase activity had been reached. To investigate this relationship also under conditions where the insulin effect on activation of receptor kinase was decreased, the adipocytes were exposed to 10 microM-isoprenaline alone or with 5 micrograms of adenosine deaminase/ml. An approx. 30% (isoprenaline) or approx. 50% (isoprenaline + adenosine deaminase) decrease in the insulin effect on receptor kinase activity was found at insulin concentrations between 0.4 and 20 ng/ml, and this could not be explained by decreased insulin binding. The decreased insulin-effect on kinase activity was closely correlated with a loss of insulin-sensitivity of glucose uptake. Moreover, our data indicate that the relation between receptor kinase activity and glucose uptake (expressed as percentage of maximal uptake) remained unchanged. The following conclusions were drawn. (1) If activation of receptor kinase stimulates glucose uptake, only 14% of the maximal kinase activity is sufficient for maximal stimulation. (2) Isoprenaline decreases the coupling efficiency between insulin binding and receptor-kinase activation, this being accompanied by a corresponding decrease in sensitivity of glucose uptake. (3) Our data indicate that the signalling for glucose uptake is closely related to receptor-kinase activity, even when the coupling efficiency between insulin binding and kinase activation is altered. They thus support the hypothesis that receptor-kinase activity reflects the signal which originates from the receptor and which is transduced to the glucose-transport system.

3-O-Methylglucose↗
PubMed1991

Association of Metformin's effect to increase insulin-stimulated glucose transport with potentiation of insulin-induced translocation of glucose transporters from intracellular pool to plasma membrane in rat adipocytes.

To examine the cellular mechanism of the antihyperglycemic action of metformin, we studied its effect on various functional and molecular parameters involved in the pathogenesis of insulin resistance. Isolated rat adipocytes were incubated with or without metformin (1-100 micrograms/ml) for 2 h at 37 degrees C followed by an incubation with or without insulin (1.72 nM). Metformin treatment had no significant effect on basal 3-O-methylglucose uptake. In contrast, metformin increased insulin-stimulated glucose transport in a dose-dependent manner up to 43 +/- 7%. This effect was neither associated with a significant effect of metformin on trace insulin binding (1.74 +/- 0.20% without metformin vs. 1.89 +/- 0.30% with metformin; P greater than 0.05) nor with an effect of metformin on insulin-receptor kinase activity as measured by 32P incorporation into the 95,000-Mr beta-subunit of the insulin receptor and an exogenous substrate, histone 2B.(ABSTRACT TRUNCATED AT 250 WORDS)

3-O-Methylglucose↗
PubMed1991

Evidence that metformin ameliorates cellular insulin-resistance by potentiating insulin-induced translocation of glucose transporters to the plasma membrane.

To examine the cellular mechanism of the antihyperglycemic action of metformin we studied the effect of metformin on various functional and molecular parameters involved in the pathogenesis of insulin resistance. Isolated rat adipocytes were incubated with or without metformin (1-100 micrograms/ml) for 2 hours at 37 degrees C followed by an incubation with or without insulin (10 ng/ml). Metformin treatment had no significant effect on basal 3-0 methylglucose uptake. In contrast, Metformin increased insulin-stimulated glucose transport in a dose dependent manner up to 43 +/- 7%. This effect was neither associated with a significant effect of Metformin on trace insulin binding, 1.74 +/- .2% (-M) vs. 1.89 +/- .3% (+M), P greater than 0.05, nor with an effect of metformin on in vivo activation of insulin receptor kinase activity as measured by 32P-incorporation into the 95 kDa beta-subunit of the insulin receptor and an exogenous substrate, histone 2B. Determination of glucose transporter numbers in subcellular membrane fractions, plasma membranes and low-density microsomes, using cytochalasin B binding and immunodetection revealed that metformin's effect to increase insulin-stimulated glucose transport is associated with a potentiation (38 +/- 5%) of insulin-induced translocation of glucose transporters from the intracellular pool to the plasma membrane, while the basal state was not significantly affected. Determination of specific glucose transporter mRNA-levels revealed that this metformin effect is not associated with an increase in glucose transporter gene expression.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗
PubMed1990

Potential mechanism of insulin resistance in ageing: impaired insulin-stimulated glucose transport due to a depletion of the intracellular pool of glucose transporters in Fischer rat adipocytes.

To examine the cellular mechanism responsible for impaired insulin action in ageing, we determined various in-vitro parameters involved in the pathogenesis of insulin resistance, i.e. basal and insulin-stimulated [14C]3-O-methylglucose transport (3OMG), 125I-labelled insulin binding, activation of insulin receptor kinase (IRKA) in intact cells, and number and subcellular distribution of glucose transporters in subcellular membrane fractions of adipocytes from 6- (FR-6) and 24- (FR-24) month-old Fischer rats. Ageing had no effect on basal 3OMG (12 +/- 4 vs 13 +/- 3 fmol/5 x 10(4) cells, means +/- S.E.M.); in contrast, in FR-24 rats insulin-stimulated 3OMG was markedly decreased by 43% when compared with that in FR-6 rats (158 +/- 14 vs 90 +/- 8 fmol/5 x 10(4) cells; P less than 0.01). Insulin binding to adipocytes from FR-6 rats was 2.40 +/- 0.38% compared with 2.28 +/- 0.47% in FR-24 (P not significant). Moreover, ageing had no significant effect on IRKA, as determined by insulin-stimulated (0, 1, 4 and 500 ng insulin/ml) 32P-incorporation into histone 2B. In subcellular membrane fractions, low density microsomes and plasma membranes, glucose transporter numbers were determined using [3H]cytochalasin B binding and immunodetection using an antiserum against the C-terminal peptide of the hepatoma-G2-glucose transporter. Cytochalasin B binding revealed that in the basal state the intracellular pool of glucose transporters was depleted in FR-24 by about 39% compared with low density microsomes from FR-6: (48.6 +/- 7.2 vs 29.8 +/- 5.5 pmol/mg membrane protein; P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

3-O-Methylglucose↗
PubMed1989

[Noninvasive monitoring of gas exchange: methodologic prerequisites and clinical use].

The noninvasive determination of the respiratory gas exchange (measurement of oxygen uptake and carbon dioxide delivery) permits the calculation of cardiac output by Fick principle and of the actual energy requirement of the patient (indirect calorimetry). A system is presented for the continuous measurement of oxygen uptake and carbon dioxide delivery, that bases on simple components, which are available on most intensive care units. The methodical problems are discussed and the improvement of the signal of the oxygen sensor by digital signal processing is described. Clinical measurements on 16 patients are presented, whose metabolic rate early after extracorporal circulation was measured. The results reveal, that 4.4 hours after ECC the metabolic rate is close to the calculated basic metabolic rate. They demonstrate the importance of indirect calorimetry as a future bedside monitoring routine.

Anesthesia, General↗
PubMed1988

Cellular mechanisms of insulin resistance in non-insulin-dependent (type II) diabetes.

Recent studies have led to an enhanced understanding of cellular alterations that may play an important role in the pathophysiology of non-insulin-dependent diabetes mellitus (NIDDM). The insulin receptor links insulin binding at the cell surface to intracellular activation of insulin's effects. This transducer function involves the tyrosine kinase property of the beta-subunit of the receptor. It was found that adipocytes from subjects with NIDDM had a 50 to 80 percent reduction in insulin-stimulated receptor kinase activity compared with their non-diabetic counterparts. This defect was relatively specific for the diabetic state since no decrease was observed in insulin-resistant non-diabetic obese subjects. The reduction in kinase activity was accounted for by changes in the ratio of two pools of receptors, both of which bind insulin but only one of which is capable of tyrosine autophosphorylation and subsequent kinase activation; 43 percent of the receptors from non-diabetic subjects were capable of autophosphorylation compared with only 14 percent in the NIDDM group. A major component of cellular insulin resistance in NIDDM involves the glucose transport system. Exposure of cells to insulin normally results in enhanced glucose transport mediated by translocation of glucose transporters from a low-density microsomal intracellular pool to the plasma membrane. It was found that cells from NIDDM subjects had a marked depletion of glucose transporters in both plasma membranes and low-density microsomes, relative to obese non-diabetic control participants. Obese non-diabetic persons had a normal number of plasma membrane transporters but a reduced number of low-density microsome transporters in the basal state compared with lean control volunteers; insulin induced the translocation of relatively fewer transporters from the low-density microsome to the plasma membrane in the obese subgroups. In addition to the diminished number of glucose transporters, cells from both NIDDM and obese subjects had impaired functional activity of glucose carriers since decreased whole-cell glucose transport rates could not be entirely explained by the magnitude of the decrement in the number of plasma membrane transporters. Thus, impaired glucose transport is due to both a numerical and functional defect in glucose transporters. The cellular content of high-density microsomal transporters was the same in lean and obese control volunteers and NIDDM subjects, suggesting that transporter synthesis is normal and that cellular depletion results from increased protein turnover once transporters leave the high-density microsomal subfraction.(ABSTRACT TRUNCATED AT 400 WORDS)

Adipose Tissue↗
PubMed1988

Cycloheximide decreases glucose transporters in rat adipocyte plasma membranes without affecting insulin-stimulated glucose transport.

This study examines the relationship between insulin-stimulated glucose transport and insulin-induced translocation of glucose transporters in isolated rat adipocytes. Adipose cells were incubated with or without cycloheximide, a potent inhibitor of protein synthesis, for 60 min and then for an additional 30 min with or without insulin. After the incubation we measured 3-O-methylglucose transport in the adipose cells, and subcellular membrane fractions were prepared. The numbers of glucose transporters in the various membrane fractions were determined by the cytochalasin B binding assay. Basal and insulin-stimulated 3-O-methylglucose uptakes were not affected by cycloheximide. Furthermore, cycloheximide affected neither Vmax. nor Km of insulin-stimulated 3-O-methylglucose transport. In contrast, the number of glucose transporters in plasma membranes derived from cells preincubated with cycloheximide and insulin was markedly decreased compared with those from cells incubated with insulin alone (10.5 +/- 0.8 and 22.2 +/- 1.8 pmol/mg of protein respectively; P less than 0.005). The number of glucose transporters in cells incubated with cycloheximide alone was not significantly different compared with control cells. SDS/polyacrylamide-gel-electrophoretic analysis of [3H]cytochalasin-B-photolabelled plasma-membrane fractions revealed that cycloheximide decreases the amount of labelled glucose transporters in insulin-stimulated membranes. However, the apparent molecular mass of the protein was not changed by cycloheximide treatment. The effect of cycloheximide on the two-dimensional electrophoretic profile of the glucose transporter in insulin-stimulated low-density microsomal membranes revealed a decrease in the pI-6.4 glucose-transporter isoform, whereas the insulin-translocatable isoform (pI 5.6) was decreased. Thus the observed discrepancy between insulin-stimulated glucose transport and insulin-induced translocation of glucose transporters strongly suggests that a still unknown protein-synthesis-dependent mechanism is involved in insulin activation of glucose transport.

3-O-Methylglucose↗
PubMed1988

Role of glucose transporters in the cellular insulin resistance of type II non-insulin-dependent diabetes mellitus.

To examine the role of glucose transport proteins in cellular insulin resistance, we studied subcutaneous adipocytes isolated from lean control, obese control (body mass index [BMI] 33.4 +/- 0.9), and untreated obese non-insulin-dependent diabetes mellitus (NIDDM) patients (BMI 35.2 +/- 2.1; fasting glucose 269 +/- 20 mg/dl). Glucose transporters were measured in plasma membrane (PM), low-density (LDM), and high-density (HDM) microsomal subfractions from basal and maximally insulin-stimulated cells using the cytochalasin B binding assay, and normalized per milligram of membrane protein. In all subgroups, insulin led to an increase in PM glucose transporters and a corresponding depletion of transporters in the LDM. Insulin recruited 20% fewer transporters to the PM in the obese subgroup when compared with lean controls, and this was associated with a decline in LDM transporters with enlarging cell size in the control subjects. In NIDDM, PM, and LDM, transporters were decreased 50% in both basal and stimulated cells when compared with obese controls having similar mean adipocyte size. Cellular depletion of glucose transporters was not the only cause of insulin resistance, because the decrease in rates of [14C]-D-glucose transport (basal and insulin-stimulated) was greater than could be explained by reduced numbers of PM transporters in both NIDDM and obesity. In HDM, the number of transporters was not influenced by insulin and was similar in all subgroups. We conclude that (a) in NIDDM and obesity, both reduced numbers and impaired activity of glucose transporters contribute to cellular insulin resistance, and (b) in NIDDM, more profound cellular insulin resistance is associated primarily with a further depletion of cellular transporters.

Adipose Tissue↗