cytochalasin-b and Insulin-Resistance

Individuals with non-insulin dependent or insulin-dependent diabetes mellitus present insulin resistance in peripheral tissues. This is reflected in a subnormal whole body insulin-dependent glucose utilization, largely dependent on skeletal muscle. Glucose transport across the cell membrane of this tissue is rate limiting in the utilization of the hexose. Therefore, it is possible that a defect exists in insulin-dependent glucose transport in skeletal muscle in diabetic states. This review focuses on two questions: is there a defect at the level of glucose transporters in skeletal muscle of diabetic animal models, and is this a consequence of abnormal insulin or glucose levels? The latter question arises from the fact that these parameters usually vary inversely to each other. Glucose transport into skeletal muscle occurs by two membrane proteins, the GLUT1 and GLUT4 gene products. By subcellular fractionation and Western blotting with isoform-specific antibodies, it was determined that isolated plasma membranes (PM) contain GLUT4 and GLUT1 proteins at a molar ratio of 3.5:1 and that an intracellular fraction (internal membranes; IM) different from sarcoplasmic reticulum contains only GLUT4 transporters. The IM furnishes transporters to the PM in response to insulin. Both transporter isoforms bind cytochalasin B in a D-glucose-protectable fashion. In streptozocin-induced diabetes of the rat with normal fasting insulin levels and marked hyperglycemia, the number of cytochalasin B-binding sites and of GLUT4 proteins diminishes in the PM whereas the GLUT1 proteins increase to a new ratio of about 1.5:1 GLUT4:GLUT1. In the IM, the levels of GLUT4 protein drop, as does the cellular GLUT4 mRNA. To investigate if these changes are associated with hyperglycemia, glucose levels were corrected back to normal values for a 24-h period with sc injections of phlorizin to block proximal tubule glucose reabsorption. This treatment restored cytochalasin B binding, restored GLUT4 and GLUT1 values back to normal levels in the PM, and partly restored cytochalasin B binding but not GLUT4 levels in the IM, consistent with only a partial recovery of GLUT4 mRNA. It is concluded that GLUT4 protein in the PM correlates inversely whereas GLUT1 protein correlates directly with glycemia. It is proposed that the decrease in GLUT4 levels is a protective mechanism, sparing skeletal muscle from gaining glucose and experiencing diabetic complications, albeit at the expense of becoming ins

Topics: Animals; Binding, Competitive; Blood Glucose; Cytochalasin B; Diabetes Complications; Diabetes Mellitus; Diabetes Mellitus, Experimental; Gene Expression Regulation; Glucose Transporter Type 4; Glycosylation; Humans; Hyperglycemia; Insulin; Insulin Resistance; Intestinal Absorption; Kidney Tubules, Proximal; Monosaccharide Transport Proteins; Multigene Family; Muscle Proteins; Muscles; Organ Specificity; Phlorhizin; Rats; Subcellular Fractions

In this article we have described the hypothesis that insulin stimulates glucose transport through glucose transporter translocation from an intracellular pool to the plasma membrane. In addition, we have shown that changes in the numbers and subcellular distributions of glucose transporters correlate with alterations in insulin-stimulated glucose transport activity in several experimental models of insulin resistance and hyperresponsiveness. However, in experiments with counterregulatory hormones and with hyperresponsive states induced by nutritional repletion following deprivation, changes in insulin responsiveness cannot be fully explained by such alterations in the numbers and/or subcellular distribution of glucose transporters. Thus, evidence has been presented for changes in glucose transporter intrinsic activity that both inhibit and augment insulin-stimulated glucose transport rates. Finally, we have discussed data suggesting that the translocation process is applicable to human tissue and that significant changes in adipose cell glucose transport activity have been correlated with total glucose disposal in various metabolic states in humans. Determining the physiologic factors involved in modulating these events at the cellular level is an important area for further investigation.

Topics: Adipose Tissue; Aging; Animals; Biological Transport; Cell Membrane; Cytochalasin B; Diabetes Mellitus, Experimental; Fasting; Glucose; Humans; Insulin; Insulin Resistance; Microsomes; Models, Biological; Monosaccharide Transport Proteins; Muscles; Obesity

Structural maintenance of chromosomes (SMC) complexes are essential for maintaining chromatin structure and regulating gene expression. Two the three known SMC complexes, cohesin and condensin, are important for sister chromatid cohesion and condensation, respectively; however, the function of the third complex, SMC5-6, which includes the E3 SUMO-ligase NSMCE2 (also widely known as MMS21) is less clear. Here, we characterized 2 patients with primordial dwarfism, extreme insulin resistance, and gonadal failure and identified compound heterozygous frameshift mutations in NSMCE2. Both mutations reduced NSMCE2 expression in patient cells. Primary cells from one patient showed increased micronucleus and nucleoplasmic bridge formation, delayed recovery of DNA synthesis, and reduced formation of foci containing Bloom syndrome helicase (BLM) after hydroxyurea-induced replication fork stalling. These nuclear abnormalities in patient dermal fibroblast were restored by expression of WT NSMCE2, but not a mutant form lacking SUMO-ligase activity. Furthermore, in zebrafish, knockdown of the NSMCE2 ortholog produced dwarfism, which was ameliorated by reexpression of WT, but not SUMO-ligase-deficient NSMCE. Collectively, these findings support a role for NSMCE2 in recovery from DNA damage and raise the possibility that loss of its function produces dwarfism through reduced tolerance of replicative stress.

Topics: Animals; Cell Cycle Proteins; Chromosomal Proteins, Non-Histone; Cytochalasin B; Dwarfism; Female; Haplotypes; Humans; Insulin Resistance; Ligases; Mutation; RecQ Helicases; Zebrafish

The anti-obesity agent sibutramine, a serotonin and noradrenaline reuptake inhibitor (SNRI), has been shown to reduce insulin resistance and improve glycaemic control in obese-diabetic ob/ob mice and overweight type 2 diabetic patients.. To investigate whether sibutramine or its metabolites act directly on muscle cells to improve glucose uptake and insulin action.. Uptake of the non-metabolized glucose analogue 2-deoxyglucose was measured in cultured L6 rat muscle cells after incubation with sibutramine, its two pharmacologically active metabolites and related agents.. Sibutramine itself (10(-8)-10(-6) M) did not significantly affect 2-deoxyglucose uptake during incubations up to 72 h. The primary amine metabolite M2 (10(-7) and 10(-6) M) increased basal and insulin-stimulated 2-deoxyglucose uptake (by 12% and 34%) after 24 h incubation. These effects of M2 were lost by 72 h incubation. However, the secondary amine metabolite M1 (10(-6) M) increased basal and insulin-stimulated 2-deoxyglucose uptake (by 50%) after 72 h incubation, although M1 was ineffective after 24 h. M2 stimulated 2-deoxyglucose uptake in the presence of LY-294,002 (an inhibitor of phosphatidylinositol 3-kinase) but the effect of M2 was inhibited by cytochalasin B, which acutely blocks glucose transporters. Incubations with serotoninergic, noradrenergic and dopaminergic agents, or agents known to stimulate release or inhibit reuptake of these substances in nervous tissues indicated that the sibutramine metabolites were not affecting 2-deoxyglucose uptake via mechanisms associated with their SNRI properties.. Sibutramine metabolites can improve insulin-sensitive 2-deoxyglucose uptake by cultured muscle cells independently of SNRI effects.

Topics: Animals; Appetite Depressants; Area Under Curve; Biological Transport; Cells, Cultured; Chromones; Cyclobutanes; Cycloheximide; Cytochalasin B; Deoxyglucose; Enzyme Inhibitors; Glucose; Insulin; Insulin Resistance; Morpholines; Muscles; Protein Synthesis Inhibitors; Rats; Time Factors

The effects of a similar exercise training stimulus on maximal insulin-stimulated (MIS) plasma membrane glucose transporter number and glucose transport were determined in lean and obese SHHF/Mcc-facp rats. Six-week-old lean and obese male rats were randomly divided into four groups: lean sedentary (LSed), obese sedentary (OSed), lean exercise (LEx), and obese exercise (OEx). An 8- to 12-wk treadmill running program equalized daily muscular work for LEx and OEx. Plasma membranes were isolated from control and MIS muscles of mixed fiber types. MIS significantly increased glucose transport (3.4- and 2.8-fold) in LSed and OSed, respectively. MIS significantly increased glucose transporter number (2.5-fold) in LSed, but there was no increase in glucose transporter number in OSed. Peak oxygen uptake and citrate synthase activity were increased a similar amount for LEx and OEx groups, demonstrating a similar training stimulus. MIS significantly and similarly increased glucose transport in LEx and OEx (4.4- and 5.1-fold, respectively). The effects of MIS on plasma membrane glucose transporter number in the exercise-trained rats were similar to the responses observed in the sedentary lean and obese groups. MIS significantly increased glucose transporter number (2.6-fold) in LEx, whereas there was no increase in glucose transporter number in OEx. The reduction in MIS glucose transport in OSed appears to be related to a defect in the processes associated with the translocation of glucose transporters to the plasma membrane. Exercise training of the obese rats apparently did not alter this defect. Similar increases in peak oxygen uptake, citrate synthase, and MIS glucose transport in LEx and OEx groups suggest that insulin resistance does not limit the ability of the glucose transport system to adapt to exercise training in the obese male SHHF/Mcc-facp rats.

Topics: 4-Nitrophenylphosphatase; Animals; Blood Glucose; Cell Membrane; Citrate (si)-Synthase; Cytochalasin B; Glucose Transporter Type 4; Glycogen; Insulin; Insulin Resistance; Male; Monosaccharide Transport Proteins; Muscle Proteins; Muscle, Skeletal; Obesity; Organ Size; Oxygen Consumption; Physical Conditioning, Animal; Rats; Rats, Inbred Strains

We investigated the influence of altered glucose levels on insulin-stimulated 3-0-methylglucose transport in isolated skeletal muscle obtained from NIDDM patients (n = 13) and non-diabetic subjects (n = 23). Whole body insulin sensitivity was 71% lower in the NIDDM patients compared to the non-diabetic subjects (p < 0.05), whereas, insulin-mediated peripheral glucose utilization in the NIDDM patients under hyperglycaemic conditions was comparable to that of the non-diabetic subjects at euglycaemia. Following a 30-min in vitro exposure to 4 mmol/l glucose, insulin-stimulated 3-0-methylglucose transport (600 pmol/l insulin) was 40% lower in isolated skeletal muscle strips from the NIDDM patients when compared to muscle strips from the non-diabetic subjects. The impaired capacity for insulin-stimulated 3-0-methylglucose transport in the NIDDM skeletal muscle was normalized following prolonged (2h) exposure to 4 mmol/l, but not to 8 mmol/l glucose. Insulin-stimulated 3-0-methylglucose transport in the NIDDM skeletal muscle exposed to 8 mmol/l glucose was similar to that of the non-diabetic muscle exposed to 5 mmol/l glucose, but was decreased by 43% (p < 0.01) when compared to non-diabetic muscle exposed to 8 mmol/l glucose. Despite the impaired insulin-stimulated 3-0-methylglucose transport capacity demonstrated by skeletal muscle from the NIDDM patients, skeletal muscle glycogen content was similar to that of the non-diabetic subjects. Kinetic studies revel a Km for 3-0-methylglucose transport of 9.7 and 8.8 mmol/l glucose for basal and insulin-stimulated conditions, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 3-O-Methylglucose; Biological Transport; Blood Glucose; Cytochalasin B; Diabetes Mellitus, Type 2; Female; Glucose; Humans; In Vitro Techniques; Insulin; Insulin Resistance; Kinetics; Male; Methylglucosides; Middle Aged; Muscles

High-fat diet (HFD) induces skeletal muscle insulin resistance. To investigate associated changes in the plasma membrane glucose transporter, male Sprague-Dawley rats were fed either chow [high-carbohydrate diet (HCD)] or HFD for 3 wk. Plasma membrane vesicles were prepared from hindlimb muscle of control, insulin-stimulated (Ins), and acutely exercised (Ex) rats. Maximal vesicle glucose transport activity (Vmax) increased threefold with Ins and Ex treatment compared with controls in HCD rats; in HFD rats, increases were less than twofold. Transporter numbers (measured by cytochalasin B binding, CB) approximately doubled with Ins and Ex in both diet groups. Intrinsic activity (carrier turnover, Vmax/CB) increased significantly with stimulation in HCD but not HFD rats. Therefore, vesicles from HFD rats showed resistance to both exercise and insulin stimulation of muscle glucose transport. Transporter number increased normally, but intrinsic activity in HFD rats did not respond. Two conclusions are discussed: 1) translocation and activation are distinct, separable steps in transporter stimulation and 2) HFD produces effects that resemble the insulin resistance of starvation.

Topics: 4-Nitrophenylphosphatase; Animals; Blood; Body Weight; Cell Membrane; Cytochalasin B; Dietary Carbohydrates; Dietary Fats; Glucose Transporter Type 4; Insulin; Insulin Resistance; Male; Monosaccharide Transport Proteins; Muscle Proteins; Muscles; Physical Exertion; Potassium; Rats; Rats, Sprague-Dawley

The genetically obese Zucker rat (fa/fa) is characterized by a severe resistance to the action of insulin to stimulate skeletal muscle glucose transport. The goal of the present study was to identify whether the defect associated with this insulin resistance involves an alteration of transporter translocation and/or transporter activity. Various components of the muscle glucose transport system were investigated in plasma membranes isolated from basal or maximally insulin-treated skeletal muscle of lean and obese Zucker rats. Measurements of D- and L-glucose uptake by membrane vesicles under equilibrium exchange conditions indicated that insulin treatment resulted in a four-fold increase in the Vmax for carrier-mediated transport for lean animals [from 4.5 to 17.5 nmol/(mg.s)] but only a 2.5-fold increase for obese rats [from 3.6 to 9.1 nmol/(mg.s)]. In the lean animals, this increase in glucose transport function was associated with a 1.8-fold increase in the transporter number as indicated by cytochalasin B binding, a 1.4-fold increase in plasma membrane GLUT4 protein, and a doubling of the average carrier turnover number (intrinsic activity). In the obese animals, there was no change in plasma membrane transporter number measured by cytochalasin B binding, or in GLUT4 or GLUT1 protein. However, there was an increase in carrier turnover number similar to that seen in the lean litter mates. Measurements of GLUT4 mRNA in red gastrocnemius muscle showed no difference between lean and obese rats. We conclude that the insulin resistance of the obese rats involves the failure of translocation of transporters, while the action of insulin to increase the average carrier turnover number is normal.

Topics: Animals; Biological Transport; Blood Glucose; Cell Membrane; Cytochalasin B; Glucose; Insulin; Insulin Resistance; Monosaccharide Transport Proteins; Muscles; Obesity; Phosphorylation; Rats; Rats, Zucker; RNA, Messenger

The subcellular distribution of glucose transporters in rat hepatocytes and HepG2 cells was studied in the absence and in the presence of insulin. Glucose transporters were quantitated by measuring glucose-sensitive cytochalasin B binding and by protein immunoblotting using isoform-specific antibodies. Plasma membrane contamination into subcellular fractions was assessed by measuring distribution of 5'-nucleotidase and cell surface carbohydrate label. In hepatocytes, GLUT-2 occurred in a low-density microsomal (LDM) fraction at a significant concentration, and as much as 15% of cellular GLUT-2 was found intracellularly that cannot be accounted for by plasma membrane contamination. In HepG2 cells which express GLUT-1 and GLUT-2, the two isoforms showed distinct subcellular distribution patterns: GLUT-2 was highly concentrated in LDM while very little GLUT-1 was found in this fraction, indicating that a large portion of GLUT-2 occurs in intracellular organelles. Insulin treatment did not change the subcellular distribution patterns of glucose transporters in both cell types. Our results suggest that rat hepatocytes and HepG2 cells possess an intracellular storage pool for GLUT-2, but lack the insulin-responsive glucose transporter translocation mechanism.

Topics: Adipose Tissue; Animals; Biological Transport; Blotting, Western; Borohydrides; Cell Fractionation; Cell Membrane; Cells, Cultured; Cytochalasin B; Glucose; Humans; Insulin; Insulin Resistance; Isomerism; Liver; Liver Neoplasms; Microsomes, Liver; Monosaccharide Transport Proteins; Organelles; Rats; Rats, Inbred Strains; Tumor Cells, Cultured

Primary cultured cardiac myocytes from adult rats were used to elucidate the role of insulin and catecholamines in the development of insulin resistance in this tissue. Cardiomyocytes exhibited a stable response toward insulin up to at least 48 h in serum-free culture, as determined by measuring the effect of the hormone on initial rates of 2-deoxyglucose uptake. Culturing of cells in the absence of insulin for 6 and 19 h, respectively, resulted in a loss of insulin sensitivity and a reduced (33%) maximal responsiveness after 19 h of insulin deficiency. This was paralleled by a decrease in [14C]phenylalanine incorporation and an unaltered level of insulin binding. Insulin action was completely lost in cells cultured in the presence of cycloheximide for 19 h. When added to the culture medium for 4 h, both isoproterenol and (Bu)2cAMP decreased insulin binding by about 50%. Under these conditions maximal insulin responsiveness was not affected by isoproterenol but was reduced by 46% by (Bu)2cAMP. Nifedipine antagonized the inhibitory action of (Bu)2cAMP, but was ineffective when the culture period was extended to 19 h. Cardiomyocytes cultured in the presence of palmitate exhibited a largely reduced (67%) insulin responsiveness, which was only partly restored by inhibition of fatty acid oxidation. From these data we conclude that: 1) insulin deficiency induces insulin resistance due to decreased protein synthesis; 2) sustained, prolonged elevation of cAMP modulates insulin action by both Ca(++)-dependent and Ca(++)-independent mechanisms; and 3) free fatty acids antagonize insulin action by both metabolic and nonmetabolic pathways.

Topics: Animals; Biological Transport; Bucladesine; Cells, Cultured; Cyclic AMP; Cycloheximide; Cytochalasin B; Deoxyglucose; Fatty Acids; Heart; Insulin; Insulin Resistance; Isoproterenol; Male; Myocardium; Nifedipine; Phenylalanine; Phosphorylation; Rats; Rats, Inbred Strains

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)

Topics: 3-O-Methylglucose; Adipose Tissue; Aging; Animals; Blood Glucose; Cytochalasin B; In Vitro Techniques; Insulin; Insulin Resistance; Male; Methylglucosides; Monosaccharide Transport Proteins; Protein-Tyrosine Kinases; Rats; Rats, Inbred F344; Receptor, Insulin; Subcellular Fractions

Obesity is known to be associated with insulin resistance in human and rat adipocytes. However, it is not known what are the perturbations in insulin action that contribute to disproportional femoral obesity. Thus femoral subcutaneous adipose tissue was obtained from lean women with various degrees of disproportional obesity, by liposuction. 3-O-methylglucose (3-O-methyl-D-glucopyranose) transport was measured in intact cells, and glucose transporter levels in plasma and low-density microsomal membranes were assessed using the cytochalasin B binding assay. A sixfold cellular enlargement was associated with increase in both basal and insulin-stimulated glucose transport activity in the intact cell, and a 300-600% increase in insulin stimulating effect per se. However, when glucose transporter levels were assessed, this cellular enlargement was accompanied by a 40-70% transporter depletion (in largest cells compared with smallest ones) in both subcellular fractions examined, from either basal or insulin-stimulated cells. This discrepancy, between increasing cellular glucose transport rates and relative depletion of transporter levels, suggests that these cells are not insulin resistant, as could be expected from their large size. A role for other factor(s), additional to glucose transporter levels, in the regulation of cellular glucose uptake rate is thus suggested.

Topics: 3-O-Methylglucose; Adipose Tissue; Biological Transport; Cell Membrane; Cytochalasin B; Female; Femur; Glucose; Humans; Insulin; Insulin Resistance; Intracellular Membranes; Methylglucosides; Microsomes; Monosaccharide Transport Proteins

To clarify the mechanism(s) responsible for the insulin resistance in streptozotocin (STZ)-treated diabetic rats, we studied insulin-induced glucose disposal by using the glucose clamp technique and measured insulin receptor and glucose transporter of muscles. The insulin dose-response curve of the metabolic clearance rate (MCR) of glucose revealed a decrease of the maximal response without a rightward shift in STZ rats. Maximal MCR was even lower when clamped at 300 rather than 150 mg/dl of blood glucose levels. Insulin binding to the crude plasma membrane of muscles from STZ rats was increased compared with controls. The number of glucose transporter of the plasma and microsomal membranes were significantly decreased in STZ rats. These in vivo and in vitro studies using skeletal muscles suggest that in STZ-treated diabetic rats 1) a defect or defects exist in the signal transduction mechanism of insulin in postbinding steps, 2) the decreased maximal MCR is related at least partly to the decrease of glucose transporter numbers, and 3) a defect in glucose metabolism (postglucose transport defect) is also present.

Topics: Animals; Cytochalasin B; Diabetes Mellitus, Experimental; Glucose; Insulin; Insulin Resistance; Liver; Male; Monosaccharide Transport Proteins; Rats; Rats, Inbred Strains; Receptor, Insulin

To further define the cellular alteration(s) involved in the impaired glucose transport associated with chronic uremia, we examined the concentration and translocation of glucose transport systems in adipocytes isolated from partially nephrectomized uremic rats. Uremic animals, compared with matched controls, had increased blood urea nitrogen and serum insulin, whereas serum glucose was unchanged. In agreement with previous work, 125I-insulin binding to its receptor was unaltered and transport of 2-deoxy-D-glucose was decreased in both the absence (basal) and presence of a maximal (7 nM) insulin concentration by 44 and 35%, respectively. To assess the movement and concentration of glucose transport systems in various membrane fractions prepared from basal and insulin-treated (20 nM) uremic fat cells, the technique of D-glucose-inhibitable cytochalasin B binding was utilized. In plasma membranes isolated from these cells the concentration of glucose transporters was decreased by 16 (P less than 0.01) and 30% (P less than 0.005) in basal and insulin-treated cells, respectively. Concomitantly, microsomal membranes prepared from uremic cells treated in the absence and presence of insulin had a 28 (P less than 0.01) and 15% (P less than 0.05) decrease in concentration of glucose transport systems, respectively. Additionally, glucose transporter concentration was significantly decreased by 17% (P less than 0.025) in total membranes prepared from uremic cells. Thus, impairment of glucose transport in uremic fat cells can be attributed to a postbinding defect that, at least in part, results from a decrease in the total concentration of glucose transporters.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adipose Tissue; Animals; Cell Membrane; Cytochalasin B; Glucose; Insulin; Insulin Resistance; Intracellular Membranes; Male; Microsomes; Monosaccharide Transport Proteins; Nephrectomy; Rats; Rats, Inbred Strains; Receptor, Insulin; Reference Values; Uremia

To determine the role of insulin in reversing the insulin resistance associated with depletion of the intracellular pool of glucose transporters, streptozocin-induced diabetic rats were treated with 5 U/day s.c. of insulin for 0, 8, or 14 days. At each time point, adipose cells were isolated, and 3-O-methylglucose transport was measured in the absence and presence of 1000 microU/ml insulin. With the cytochalasin B-binding assay, concentrations of glucose transporters in the plasma and the low-density microsomal membrane fractions were determined. Eight-day insulin therapy enhanced glucose transport rate (mean +/- SE) from 0.2 +/- 0.0 to 1.1 +/- 0.1 fmol X cell-1 X min-1 in the basal state and from 0.8 +/- 0.1 to 5.5 +/- 0.4 fmol X cell-1 X min-1 in the insulin-stimulated state in untreated and treated diabetic rats, respectively; this is a 3-fold increment of glucose transport rate in both states compared with control rats. After 14-day insulin therapy, glucose-transport activity declined toward normal but still remained approximately 1.5- and 4-fold higher than control and diabetic rats, respectively. Despite the persistent enhancement of glucose transport rate, concentration of glucose transporters in the intracellular pool was restored only to its prediabetic state. Likewise, the increased concentration of glucose transporters in the plasma membranes after insulin stimulation was similar to that of control rats. Thus, we suggest that 8-14 days of insulin therapy reversed the insulin resistance in diabetic rat adipocytes by at least two mechanisms: restoration of the intracellular pool of glucose transporters and enhancement of glucose-transport activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 3-O-Methylglucose; Adipose Tissue; Animals; Binding Sites; Cytochalasin B; Diabetes Mellitus, Experimental; Insulin; Insulin Resistance; Male; Methylglucosides; Monosaccharide Transport Proteins; Rats; Rats, Inbred Strains; Subcellular Fractions

Detailed studies of a family with hyperinsulinemia are reported. The index patient, a 30-yr-old woman with polycystic ovary syndrome, presented with gestational diabetes which was completely resistant to insulin in the presence of severe endogenous hyperinsulinemia. Sensitivity to insulin was regained after delivery. Therapy with cyproterone acetate and ethinyl estradiol for hirsutism exacerbated the hyperinsulinemia toward the levels occurring in pregnancy, with a concomitant deterioration of glucose tolerance. Five other members of her family also were found to have hyperinsulinemia together with high concentrations of circulating C-peptide. Antibodies to insulin and to insulin receptors were not detected, insulin antagonists were not increased, and insulin degradation in the circulation was normal. Insulin extracted from the patient's serum was identical to normal insulin by the criteria of Sephadex chromatography, placental membrane insulin receptor binding, and stimulation of 2-deoxyglucose uptake in isolated rat adipocytes. Although [125I]insulin binding to erythrocytes of all family members and to the patient's placental membranes was markedly reduced, binding to fibroblast cultures from the patient was normal. Insulin-stimulated glucose transport in these fibroblasts also was normal, but there was a mild (20%) reduction in the concentration of cytochalasin B-binding sites in erythrocyte ghosts. Insulin resistance in this family may be due to a partial defect distal to the insulin receptor. This is asymptomatic unless metabolic stresses (pregnancy or steroid administration) are superimposed.

Topics: Adult; C-Peptide; Cytochalasin B; Erythrocytes; Female; Fibroblasts; Hirsutism; Humans; Insulin; Insulin Antibodies; Insulin Resistance; Peptides; Placenta; Polycystic Ovary Syndrome; Pregnancy; Pregnancy Complications; Pregnancy in Diabetics; Receptor, Insulin; Somatomedins