Showing papers on "Insulin resistance published in 1992"

Pathogenesis of NIDDM: A balanced overview

Abstract: Non-insulin-dependent diabetes mellitus (NIDDM) results from an imbalance between insulin sensitivity and insulin secretion. Both longitudinal and cross-sectional studies have demonstrated that the earliest detectable abnormality in NIDDM is an impairment in the body's ability to respond to insulin. Because the pancreas is able to appropriately augment its secretion of insulin to offset the insulin resistance, glucose tolerance remains normal. With time, however, the beta-cell fails to maintain its high rate of insulin secretion and the relative insulinopenia (i.e., relative to the degree of insulin resistance) leads to the development of impaired glucose tolerance and eventually overt diabetes mellitus. The cause of pancreatic "exhaustion" remains unknown but may be related to the effect of glucose toxicity in a genetically predisposed beta-cell. Information concerning the loss of first-phase insulin secretion, altered pulsatility of insulin release, and enhanced proinsulin-insulin secretory ratio is discussed as it pertains to altered beta-cell function in NIDDM. Insulin resistance in NIDDM involves both hepatic and peripheral, muscle, tissues. In the postabsorptive state hepatic glucose output is normal or increased, despite the presence of fasting hyperinsulinemia, whereas the efficiency of tissue glucose uptake is reduced. In response to both endogenously secreted or exogenously administered insulin, hepatic glucose production fails to suppress normally and muscle glucose uptake is diminished. The accelerated rate of hepatic glucose output is due entirely to augmented gluconeogenesis. In muscle many cellular defects in insulin action have been described including impaired insulin-receptor tyrosine kinase activity, diminished glucose transport, and reduced glycogen synthase and pyruvate dehydrogenase. The abnormalities account for disturbances in the two major intracellular pathways of glucose disposal, glycogen synthesis, and glucose oxidation. In the earliest stages of NIDDM, the major defect involves the inability of insulin to promote glucose uptake and storage as glycogen. Other potential mechanisms that have been put forward to explain the insulin resistance, include increased lipid oxidation, altered skeletal muscle capillary density/fiber type/blood flow, impaired insulin transport across the vascular endothelium, increased amylin, calcitonin gene-related peptide levels, and glucose toxicity.

Prospective Analysis of The Insulin-Resistance Syndrome (Syndrome X)

Abstract: Many studies have shown that hyperinsulinemia and/or insulin resistance are related to various metabolic and physiological disorders including hypertension, dyslipidemia, and non-insulin-dependent diabetes mellitus. This syndrome has been termed Syndrome X. An important limitation of previous studies has been that they all have been cross sectional, and thus the presence of insulin resistance could be a consequence of the underlying metabolic disorders rather than its cause. We examined the relationship of fasting insulin concentration (as an indicator of insulin resistance) to the incidence of multiple metabolic abnormalities in the 8-yr follow-up of the cohort enrolled in the San Antonio Heart Study, a population-based study of diabetes and cardiovascular disease in Mexican Americans and non-Hispanic whites. In univariate analyses, fasting insulin was related to the incidence of the following conditions: hypertension, decreased high-density lipoprotein cholesterol concentration, increased triglyceride concentration, and non-insulin-dependent diabetes mellitus. Hyperinsulinemia was not related to increased low-density lipoprotein or total cholesterol concentration. In multivariate analyses, after adjustment for obesity and body fat distribution, fasting insulin continued to be significantly related to the incidence of decreased high-density lipoprotein cholesterol and increased triglyceride concentrations and to the incidence of non-insulin-dependent diabetes mellitus. Baseline insulin concentrations were higher in subjects who subsequently developed multiple metabolic disorders. These results were not attributable to differences in baseline obesity and were similar in Mexican Americans and non-Hispanic whites. These results support the existence of a metabolic syndrome and the relationship of that syndrome to multiple metabolic disorders by showing that elevations of insulin concentration precede the development of numerous metabolic disorders.

Role of Reduced Suppression of Glucose Production and Diminished Early Insulin Release in Impaired Glucose Tolerance

Abstract: Background. Insulin resistance and impaired insulin secretion both occur in non-insulin-dependent diabetes (NIDDM), but their relative importance is unclear. Hyperglycemia itself has adverse effects on tissue insulin sensitivity and insulin secretion that make it difficult to distinguish between primary and secondary abnormalities. To avoid this problem we studied subjects with postprandial glucose intolerance but not sustained hyperglycemia. Methods. We compared the rate of systemic appearance and disappearance of glucose, the output of endogenous hepatic glucose, splanchnic and muscle uptake of glucose, and plasma insulin and glucagon responses after the ingestion of 1 g of glucose per kilogram of body weight in 15 subjects with impaired glucose tolerance (8 of them nonobese and 7 obese) and in 16 normal subjects (9 nonobese and 7 obese) who were matched for age and weight. Results. After glucose ingestion the mean (±SE) rate of total systemic appearance of glucose was significantly higher in b...

Diabetes mellitus and hypertension.

Abstract: Diabetes mellitus and hypertension are common diseases that coexist at a greater frequency than chance alone would predict. Hypertension in the diabetic individual markedly increases the risk and accelerates the course of cardiac disease, peripheral vascular disease, stroke, retinopathy, and nephropathy. Our understanding of the factors that markedly increase the frequency of hypertension in the diabetic individual remains incomplete. Diabetic nephropathy is an important factor involved in the development of hypertension in diabetics, particularly type I patients. However, the etiology of hypertension in the majority of diabetic patients cannot be explained by underlying renal disease and remains "essential" in nature. The hallmark of hypertension in type I and type II diabetics appears to be increased peripheral vascular resistance. Increased exchangeable sodium may also play a role in the pathogenesis of blood pressure in diabetics. There is increasing evidence that insulin resistance/hyperinsulinemia may play a key role in the pathogenesis of hypertension in both subtle and overt abnormalities of carbohydrate metabolism. Population studies suggest that elevated insulin levels, which often occurs in type II diabetes mellitus, is an independent risk factor for cardiovascular disease. Other cardiovascular risk factors in diabetic individuals include abnormalities of lipid metabolism, platelet function, and clotting factors. The goal of antihypertensive therapy in the patient with coexistent diabetes is to reduce the inordinate cardiovascular risk as well as lowering blood pressure.

The effects of testosterone treatment on body composition and metabolism in middle-aged obese men.

Abstract: Twenty-three middle-aged abdominally obese men were treated for eight months with testosterone or with placebo. Testosterone treatment was followed by a decrease of visceral fat mass, measured by computerized tomography, without a change in body mass, subcutaneous fat mass or lean body mass. Insulin resistance, measured by the euglycemic/hyperinsulinemic glucose clamp method, improved and blood glucose, diastolic blood pressure and serum cholesterol decreased with testosterone treatment. A small increase in prostate volume was noted, but serum prostate specific antigen concentrations were unchanged and no adverse functional side-effects were found. Insulin sensitivity improved more in men with relatively low testosterone values at the outset. The mechanisms involved in these changes might act either via effects on visceral fat accumulation, followed by metabolic improvements, and/or via direct effects on muscle insulin sensitivity, as suggested by results of other recent studies. It is concluded that testosterone treatment of middle-aged abdominally obese men gives beneficial effects on well-being and the cardiovascular and diabetes risk profile, results similar to those observed after hormonal replacement therapy in postmenopausal women.

Evidence for Distinctive and Intrinsic Defects in Insulin Action in Polycystic Ovary Syndrome

Abstract: Women with PCO have a unique but poorly characterized disorder of insulin action. Obese (n = 16) and nonobese (n = 14) PCO women and age- and weight-matched normal, nondiabetic ovulatory women (obese, n = 15; nonobese, n = 17) had insulin action determined in vivo with sequential multiple insulin dose euglycemic clamps and in isolated abdominal adipocytes to clarify the mechanisms of insulin resistance. PCO resulted in significant increases in the ED50 insulin for glucose utilization in vivo (P less than 0.001) and in adipocytes (P less than 0.01), without significant changes in adipocyte insulin-binding sites. PCO also resulted in significant decreases in maximal insulin-stimulated rates of glucose utilization in vivo (P less than 0.01) and in adipocytes (P less than 0.01). Obesity resulted in smaller decreases in insulin sensitivity than PCO (ED50 insulin, P less than 0.001 in vivo and P less than 0.05 in adipocytes), but greater decreases in insulin responsiveness (Vmax, P less than 0.001 in vivo and in adipocytes). The ED50 insulin for suppression of HGP was increased only in obese PCO women (P less than 0.001), and the interactions between PCO and obesity on this parameter were statistically significant. No significant correlations between androgen or estrogen levels and adipocyte insulin binding or action were found. Because insulin binding was not changed, we conclude that the major lesion causing insulin resistance in PCO is a striking decrease in insulin sensitivity secondary to a defect in the insulin receptor and/or postreceptor signal transduction. PCO also is associated with modest but significant decreases in glucose transport. These defects in insulin action appear to represent intrinsic abnormalities that are independent of obesity, metabolic derangements, body fat topography, and sex hormone levels. Conversely, changes in hepatic insulin sensitivity appear to be acquired with obesity.

Metabolic Effects of New Oral Hypoglycemic Agent CS-045 in NIDDM Subjects

Abstract: Objective — To study the metabolic effects of a new oral antidiabetic agent, CS-045, in subjects with non-insulin-dependent diabetes mellitus (NIDDM). Research Design And Methods — Eleven NIDDM subjects (mean age 59 yr and body mass index 32.3) were treated with 400 mg/day CS-045 for 6-12 wk. Patients were hospitalized before and at the end of the drug-treatment period for metabolic studies, including oral glucose tolerance test (OGTT), meal tolerance test (MTT), euglycemic glucose-clamp studies, and lipid analyses. Results — Eight subjects showed a marked clinical response to the drug, whereas 3 were nonresponders. The data were analyzed both for the total group and for the responders. Fasting plasma glucose (FPG) fell from 12.5 ± 0.7 to 10.7 ± 1.0 mM in the total group but fell more dramatically from 12.7 ± 0.5 to 8.3 ± 0.6 mM in the responder group. The area under the OGTT glucose curve improved by 17% in the total group and by 29% in the responders. The area under the MTT glucose curve improved by 38 and 52%, respectively. MTT levels of insulin, free fatty acids, and glucagon were significantly lower after treatment. Glucose disposal rates during glucose-clamp studies were increased in all subjects after CS-045 treatment. Mean increases were 63% at 120 mU · m −2 · min −1 and 41% at 300 mU · m −2 · min −1 . Basal hepatic glucose production fell by 17% in the total group and by 28% in the responders. Conclusions — CS-045 improves insulin resistance, reduces insulinemia, lowers hepatic glucose production, and improves both fasting and postprandial glycemia in NIDDM subjects. CS-045 may represent a new therapeutic option for NIDDM.

Prospective Analysis of the Insulin-Resistance Syndrome (Syndrome X)

Abstract: Many studies have shown that hyperinsulinemia and/or insulin resistance are related to various metabolic and physiological disorders including hypertension, dyslipidemia, and non-insulin-dependent diabetes mellitus. This syndrome has been termed Syndrome X. An important limitation of previous studies has been that they all have been cross sectional, and thus the presence of insulin resistance could be a consequence of the underlying metabolic disorders rather than its cause. We examined the relationship of fasting insulin concentration (as an indicator of insulin resistance) to the incidence of multiple metabolic abnormalities in the 8-yr follow-up of the cohort enrolled in the San Antonio Heart Study, a population-based study of diabetes and cardiovascular disease in Mexican Americans and non-Hispanic whites. In univariate analyses, fasting insulin was related to the incidence of the following conditions: hypertension, decreased high-density lipoprotein cholesterol concentration, increased triglyceride concentration, and non-insulin-dependent diabetes mellitus. Hyperinsulinemia was not related to increased low-density lipoprotein or total cholesterol concentration. In multivariate analyses, after adjustment for obesity and body fat distribution, fasting insulin continued to be significantly related to the incidence of decreased high-density lipoprotein cholesterol and increased triglyceride concentrations and to the incidence of non-insulin-dependent diabetes mellitus. Baseline insulin concentrations were higher in subjects who subsequently developed multiple metabolic disorders. These results were not attributable to differences in baseline obesity and were similar in Mexican Americans and non-Hispanic whites. These results support the existence of a metabolic syndrome and the relationship of that syndrome to multiple metabolic disorders by showing that elevations of insulin concentration precede the development of numerous metabolic disorders.

Pathogenesis of Type 2 (non-insulin dependent) diabetes mellitus : a balanced overview

Abstract: Following an overnight fast the majority of glucose disposal occurs in insulin-independent tissues, the brain (-50 % ) and splanchnic organs (-25 %), while only 25 % occurs in insulin-dependent tissues, primarily muscle [14]. Basal glucose utilization (-2 mg.kg -~.min 1) is precisely matched by glucose production by the liver [1-4]. Following glucose ingestion, the balance between uptake and output is disrupted and maintenance of glucose homeostasis depends upon three processes that must occur in a co-ordinated fashion: (1) insulin secretion; (2) stimulation of glucose uptake by splanchnic (liver and gut) and peripheral (primarily muscle) tissues in response to hyperinsulinaemia plus hyperglycaemia; (3) suppression of hepatic glucoseproduction. It logically follows that abnormalities at the level of the Beta cell, muscle, and/or liver can lead to the development of glucose intolerance. The full blown syndrome of Type 2 (non-insulin-dependent) diabetes mellitus requires the simultaneous presence of two defects, insulin resistance and impaired Beta-cell function. In Type 2 diabetes the primary or inherited defect most likely represents impaired tissue (muscle and/or liver) sensitivity to insulin. Eventually, however, the Beta cell fails to maintain a sufficiently high rate of insulin secretion to compensate for the insulin resistance, and overt diabetes mellitus ensues.

Insulin resistance and breast‐cancer risk

Abstract: Life-style has a major influence on the incidence of breast cancer. To evaluate the effects of life-style related metabolic-endocrine factors on breast cancer risk we conducted a case-control study comparing 223 women aged 38 to 75 years presenting with operable (stage I or II) breast cancer and 441 women of the same age having no breast cancer, who participated in a population-based breast cancer screening program. Women reporting diabetes mellitus were excluded. Sera from 110 women of the same age group presenting with early stage melanoma, lymphoma or cervical cancer were used as a second ‘other-cancer control group’. Serum levels of C-peptide were significantly higher in early breast cancer cases compared to controls. The same was found for the ratios C-peptide to glucose or C-peptide to fructosamine, indicating insulin resistance. Sex hormone binding globulin was inversely, triglycerides and available estradiol were positively related to C-peptide. Serum C-peptide levels were related to body mass index (BMI), and to waist/hip ratio (WHR), in particular in controls. However, the relative increase of C-peptide, C-peptide to glucose or C-peptide to fructosamine in cases was independent of BMI or WHR. The log relative risk was linearly related to the log C-peptide levels. Relative risk according to quintiles, and adjusted for age, family history, BMI and WHR, for women at the 80% level was 2.9 as compared with those at the 20% level for C-peptide. Elevated C-peptide or C-peptide to fructosamine values were not observed in the sera from women belonging to the ‘other-cancer control group’. This study suggests that hyperinsulinemia with insulin resistance is a significant risk factor for breast cancer independent of general adiposity or body fat distribution. © 1992 Wiley-Liss, Inc.

Cellular mechanisms of insulin resistance in polycystic ovarian syndrome.

Abstract: Insulin resistance is a predominant feature in women with polycystic ovarian syndrome (PCO). The cellular mechanisms for this insulin resistance have not been defined. In this study, major steps in the insulin action cascade, receptor binding, kinase activity, and glucose transport activity were evaluated in isolated adipocytes prepared from PCO subjects (n = 8) without acanthosis nigricans and in a group of age and weight-matched controls [normal cycling (NC) n = 8]. The PCO group was hyperinsulinemic and displayed elevated insulin responses to an iv glucose load. The binding of 125I-insulin to adipocytes was similar in cells from PCO and NC subjects. In PCO, autophosphorylation of the insulin receptor-subunit in the absence of insulin was normal but a significant decrease (30% below control) in maximal insulin stimulated autophosphorylation was observed. However, receptor kinase activity measured against the exogenous substrate poly glu:tyr (4:1) was normal. Cells from PCO subjects transported glucose a...

Regulation of insulin receptor substrate-1 in liver and muscle of animal models of insulin resistance.

Abstract: Insulin rapidly stimulates tyrosine phosphorylation of a protein of approximately 185 kD in most cell types. This protein, termed insulin receptor substrate-1 (IRS-1), has been implicated in insulin signal transmission based on studies with insulin receptor mutants. In the present study we have examined the levels of IRS-1 and the phosphorylation state of insulin receptor and IRS-1 in liver and muscle after insulin stimulation in vivo in two rat models of insulin resistance, i.e., insulinopenic diabetes and fasting, and a mouse model of non-insulin-dependent diabetes mellitus (ob/ob) by immunoblotting with anti-peptide antibodies to IRS-1 and anti-phosphotyrosine antibodies. As previously described, there was an increase in insulin binding and a parallel increase in insulin-stimulated receptor phosphorylation in muscle of fasting and streptozotocin-induced (STZ) diabetic rats. There was also a modest increase in overall receptor phosphorylation in liver in these two models, but when normalized for the increase in binding, receptor phosphorylation was decreased, in liver and muscle of STZ diabetes and in liver of 72 h fasted rats. In the hyperinsulinemic ob/ob mouse there was a decrease in insulin binding and receptor phosphorylation in both liver and muscle. The tyrosyl phosphorylation of IRS-1 after insulin stimulation reflected an amplification of the receptor phosphorylation in liver and muscle of hypoinsulinemic animals (fasting and STZ diabetes) with a twofold increase, and showed a significant reduction (approximately 50%) in liver and muscle of ob/ob mouse. By contrast, the levels of IRS-1 protein showed a tissue specific regulation with a decreased level in muscle and an increased level in liver in hypoinsulinemic states of insulin resistance, and decreased levels in liver in the hyperinsulinemic ob/ob mouse. These data indicate that: (a) IRS-1 protein levels are differentially regulated in liver and muscle; (b) insulin levels may play a role in this differential regulation of IRS-1; (c) IRS-1 phosphorylation depends more on insulin receptor kinase activity than IRS-1 protein levels; and (d) reduced IRS-1 phosphorylation in liver and muscle may play a role in insulin-resistant states, especially of the ob/ob mice.

The morphology and metabolism of intraabdominal adipose tissue in men.

Abstract: Mass, morphology, and metabolism of total adipose tissue and its subcutaneous, visceral, and retroperitoneal subcompartments were examined in 16 men with a wide variation of total body fat. Computerized tomography (CT) scans showed that the intraabdominal fat mass comprised approximately 20% of total fat mass. Visceral and retroperitoneal fat masses were approximately 80% and 20% of total intraabdominal fat mass, respectively. Enlargement of intraabdominal fat depots was due to a parallel adipocyte enlargement only. Direct significant correlations were found between these adipose tissue masses and blood glucose and plasma insulin levels, blood pressure, and liver function tests, while glucose disposal rate during euglycemic glucose clamp measurements at submaximal insulin concentrations (GDR), plasma testosterone, and sex hormone-binding globulin concentrations correlated negatively. The correlations for glucose, insulin, and GDR were strongest with visceral fat mass. Adipose tissue lipid uptake, measured after oral administration of labeled oleic acid in triglyceride, was approximately 50% higher in omental than in subcutaneous adipose tissues. Adipocytes from omental fat also showed a higher lipolytic sensitivity and responsiveness to catecholamines. Furthermore, these adipocytes were less sensitive to the antilipolytic effects of insulin. Both lipid uptake and lipolytic sensitivity and responsiveness showed strong correlations (r = 0.8 to 0.9) to blood glucose and plasma insulin concentrations and also to the GDR (negative), while no such correlations were found with lipid uptake in subcutaneous or retroperitoneal abdominal adipose tissues. Taken together, these results suggest a higher turnover of lipids in visceral than in the other fat depots, which is closely correlated to systemic insulin resistance and glucose metabolism in men.

Lilly Lecture: Molecular Mechanisms of Insulin Resistance: Lessons From Patients With Mutations in the Insulin-Receptor Gene

Abstract: Insulin resistance contributes to the pathogenesis of NIDDM. We have investigated the molecular mechanisms of insulin resistance in patients with genetic syndromes caused by mutations in the insulin-receptor gene. In general, patients with two mutant alleles of the insulin-receptor gene are more severely insulin-resistant than are patients who are heterozygous for a single mutant allele. These mutations can be put into five classes, depending upon the mechanisms by which they impair receptor function. Some mutations lead to a decrease in the number of insulin receptors on the cell surface. For example, some mutations decrease the level of insulin receptor mRNA or impair receptor biosynthesis by introducing a premature chain termination codon (class 1). Class 2 mutations impair the transport of receptors through the endoplasmic reticulum and Golgi apparatus to the plasma membrane. Mutations that accelerate the rate of receptor degradation (class 5) also decrease the number of receptors on the cell surface. Other mutations cause insulin resistance by impairing receptor function--either by decreasing the affinity to bind insulin (class 3) or by impairing receptor tyrosine kinase activity (class 4). The prevalence of mutations in the insulin receptor gene is not known. However, theoretical calculations suggest that approximately 0.1-1% of the general population are heterozygous for a mutation in the insulin-receptor gene; the prevalence is likely to be higher among people with NIDDM. Accordingly, it is likely that mutations in the insulin-receptor gene may be a contributory cause of insulin resistance in a subpopulation with NIDDM.

Decreased insulin activation of glycogen synthase in skeletal muscles in young nonobese Caucasian first-degree relatives of patients with non-insulin-dependent diabetes mellitus.

Abstract: Insulin resistance in non-insulin-dependent diabetes is associated with a defective insulin activation of the enzyme glycogen synthase in skeletal muscles. To investigate whether this may be a primary defect, we studied 20 young (25 +/- 1 yr) Caucasian first-degree relatives (children) of patients with non-insulin-dependent diabetes, and 20 matched controls without a family history of diabetes. Relatives and controls had a normal oral glucose tolerance, and were studied by means of the euglycemic hyperinsulinemic clamp technique, which included performance of indirect calorimetry and muscle biopsies. Insulin-stimulated glucose disposal was decreased in the relatives (9.2 +/- 0.6 vs 11.5 +/- 0.5 mg/kg fat-free mass per (FFM) min, P less than 0.02), and was due to a decreased rate of insulin-stimulated nonoxidative glucose metabolism (5.0 +/- 0.5 vs 7.5 +/- 0.4 mg/kg fat-free mass per min, P less than 0.001). The insulin-stimulated, fractional glycogen synthase activity (0.1/10 mmol liter glucose-6-phosphate) was decreased in the relatives (46.9 +/- 2.3 vs 56.4 +/- 3.2%, P less than 0.01), and there was a significant correlation between insulin-stimulated, fractional glycogen synthase activity and nonoxidative glucose metabolism in relatives (r = 0.76, P less than 0.001) and controls (r = 0.63, P less than 0.01). Furthermore, the insulin-stimulated increase in muscle glycogen content over basal values was lower in the relatives (13 +/- 25 vs 46 +/- 9 mmol/kg dry wt, P = 0.05). We conclude that the defect in insulin activation of muscle glycogen synthase may be a primary, possibly genetically determined, defect that contributes to the development of non-insulin-dependent diabetes.

Gene Expression of GLUT4 in Skeletal Muscle From Insulin-Resistant Patients With Obesity, IGT, GDM, and NIDDM

Abstract: In obesity, impaired glucose tolerance (IGT), non-insulin-dependent diabetes mellitus (NIDDM), and gestational diabetes mellitus (GDM), defects in glucose transport system activity, contribute to insulin resistance in target tissues. In adipocytes from obese and NIDDM patients, we found that pretranslational suppression of the insulin-responsive GLUT4 glucose transporter isoform is a major cause of cellular insulin resistance; however, whether this process is operative in skeletal muscle is not clear. To address this issue, we performed percutaneous biopsies of the vastus lateralis in lean and obese control subjects and in obese patients with IGT and NIDDM and open biopsies of the rectus abdominis at cesarian section in lean and obese gravidas and gravidas with GDM. GLUT4 was measured in total postnuclear membrane fractions from both muscles by immunoblot analyses. The maximally insulin-stimulated rate of in vivo glucose disposal, assessed with euglycemic glucose clamps, decreased 26% in obesity and 74% in NIDDM, reflecting diminished glucose uptake by muscle. However, in vastus lateralis, relative amounts of GLUT4 per milligram membrane protein were similar (NS) among lean (1.0 +/- 0.2) and obese (1.5 +/- 0.3) subjects and patients with IGT (1.4 +/- 0.2) and NIDDM (1.2 +/- 0.2). GLUT4 content was also unchanged when levels were normalized per wet weight, per total protein, and per DNA as an index of cell number. Levels of GLUT4 mRNA were similarly not affected by obesity, IGT, or NIDDM whether normalized per RNA or for the amount of an unrelated constitutive mRNA species. Because muscle fibers (types I and II) exhibit different capacities for insulin-mediated glucose uptake, we tested whether a change in fiber composition could cause insulin resistance without altering overall levels of GLUT4. However, we found that quantities of fiber-specific isoenzymes (phopholamban and types I and II Ca(2+)-ATPase) were similar in all subject groups. In rectus abdominis, GLUT4 content was similar in the lean, obese, and GDM gravidas whether normalized per milligram membrane protein (relative levels were 1.0 +/- 0.2, 1.3 +/- 0.1, and 1.0 +/- 0.2, respectively) or per wet weight, total protein, and DNA. We conclude that in human disease states characterized by insulin resistance, i.e., obesity, IGT, NIDDM, and GDM, GLUT4 gene expression is normal in vastus lateralis or rectus abdominis. To the extent that these muscles are representative of total muscle mass, insulin resistance in skeletal muscle may involve impaired GLUT4 function or translocation and not transporter depletion as observed in adipose tissue.

The sympathetic response to euglycaemic hyperinsulinaemia. Evidence from microelectrode nerve recordings in healthy subjects.

Abstract: Sympathetic nervous system activation by insulin has been suggested as a mechanism explaining the association between insulin resistance and hypertension. We further examined the effect of insulin by direct microneurographic muscle and skin nerve sympathetic activity recordings during euglycaemic insulin clamps in healthy subjects. The mean plasma insulin level was elevated from 5.3±0.7 to 92.2±2.2 mU/l in seven subjects during a 90-min one-step clamp. In six other subjects plasma insulin was further raised from 85.7±4.0 mU/l to 747±53 mU/l between 45–90 min (two-step clamp). Four of the latter subjects received a sham clamp with NaCl infusions only on a second recording session. At the low dose of insulin muscle nerve sympathetic activity increased from a resting level of 22.7±5.0 bursts per min to 27.7±5.0 bursts per min at 15 min (p<0.05). The increases in muscle nerve sympathetic activity were significant (p<0.001; ANOVA) throughout insulin infusion, with a slight further increase (from 29.2±1.6 to 32.3±1.9 bursts per min) at the supraphysiological insulin concentration. During sham clamps muscle nerve sympathetic activity did not increase. Both insulin clamps induced minor, but significant, increases in forearm venous plasma noradrenaline concentrations. Skin nerve sympathetic activity (n=3) did not change during insulin infusions. Heart rate increased slightly but significantly (p<0.005), during the insulin clamps. Blood pressure was not notably affected. In conclusion, hyperinsulinaemia was associated with increased vasoconstrictor nerve activity to skeletal muscle and with no change of sympathetic outflow to skin.

Facilitative glucose transporters: regulatory mechanisms and dysregulation in diabetes.

Abstract: Introduction Maintenance of normal glucose homeostasis results from the precise orchestration ofthree processes: glucose absorption via the gut, production by the liver, and utilization by nearly all tissues in the body. In the fasting state, most ofglucose utilization is by brain and is independent of insulin. Glucose levels are maintained during a fast by the tightly regulated release of glucose from the liver. Postprandially, increased insulin levels promote enhanced glucose uptake, metabolism, and storage in muscle and adipose cells, with skeletal muscle quantitatively most important. The increment in insulin and decrement in glucagon concentrations in the portal circulation inhibit he-patic glucose production. States such as diabetes and obesity are characterized by resistance to the effect of insulin on both the stimulation of peripheral glucose utilization as well as the inhibition of hepatic glucose production. Diabetes is further marked by inadequate insulin secretion to meet the increased demands resulting from peripheral insulin resistance. In mammalian cells, glucose is not freely permeable across the lipid bilayer but enters by facilitated diffusion, a process in which specific integral membrane proteins passively transport glucose down a concentration gradient. Glucose can also be concentrated in epithelial cells of the intestine and the proxi-mal tubule ofthe kidney by an active process in which Na+/glu-cose cotransporters (reviewed in 1) utilize the electrochemical potential ofNa' as an energy source. Molecular cloning studies over the last seven years have revealed a family of facilitated diffusion glucose transporter proteins which are structurally related but are encoded by distinct genes that are expressed in a tissue specific manner (reviewed in 2-4) (Table I). These are structurally and genetically distinct from the Na+-linked glucose cotransporters but bear considerable sequence homology with sugar transporters in bacteria, yeast, and protozoa (3). Recent studies have begun to unravel the mechanisms by which facilitated diffusion transporters participate in the regulation of glucose utilization in various tissues. This Perspectives will discuss evidence that altered expression, localization, and/ or function of facilitative glucose transporters may contribute to the pathogenesis of diseases such as diabetes.

Evidence for an independent relationship between insulin resistance and fasting plasma HDL-cholesterol, triglyceride and insulin concentrations.

Abstract: Elevated plasma insulin and triglyceride (TG) and decreased high-density-lipoprotein (HDL)-cholesterol concentrations have been shown to be risk factors for coronary heart disease (CHD). It has been suggested that these metabolic abnormalities are all secondary to resistance to insulin-stimulated glucose uptake. To examine this in more detail, we divided 18 non-diabetic, moderately overweight, sedentary men aged 25-50 years into three groups on the basis of their steady-state plasma glucose levels (SSPG): a low group, (n = 7; SSPG less than 8.3 mmol l-1), a middle group, (n = 6; SSPG 8.3-11.1 mmol l-1), and a high group (n = 5; SSPG greater than 11.1 mmol l-1). The high group had significantly higher fasting (P less than 0.05) and post-oral glucose challenge (P less than 0.01) insulin concentrations, higher fasting TG (P less than 0.05) and lower fasting HDL-cholesterol (P less than 0.05) concentrations than the other two groups. However, there were no statistically significant differences between the groups with regard to body mass index, waist-to-hip ratio or physical endurance capacity as determined by maximal oxygen consumption during a treadmill test. The data suggest that insulin resistance has an effect on the modulation of plasma insulin, TG and HDL-cholesterol concentrations, independent of generalized, abdominal or physical endurance capacity.

Relationship of glucose intolerance and hyperinsulinaemia to body fat pattern in south Asians and Europeans.

Abstract: Type 2 (non-insulin-dependent) diabetes mellitus and insulin resistance are associated with centrally-distributed obesity. These disturbances are especially prevalent in people of South Asian (Indian, Pakistani and Bangladeshi) descent. We examined the relationship of glucose intolerance to body fat pattern in a population survey of 2936 men and 537 women of South Asian and European origin living in London, UK. In both groups glucose intolerance (defined as diabetes or impaired glucose tolerance) was more strongly associated with waist-hip girth ratio than with skinfolds or body mass index. The associations between body mass index and glucose intolerance were fully accounted for by waist-hip ratio. In European men with normal glucose tolerance fasting insulin levels were more strongly correlated with body mass index than with waist-hip ratio. Physical activity scores were lower in South Asians than in Europeans but no statistically significant associations between glucose intolerance and low physical activity were detectable. Leisure-time physical activity scores were inversely correlated with 2 h insulin levels in both groups. In contrast with other studies these results suggest that a specific effect of intra-abdominal fat deposition underlies the association between glucose intolerance and obesity. The association between hyperinsulinaemia and obesity is less specific for centrally-distributed fat. When measured appropriately waist-hip ratio is the most valid anthropometric index for identifying individuals whose obesity predisposes them to glucose intolerance.

The Metabolic Profile of NIDDM Is Fully Established in Glucose-Tolerant Offspring of Two Mexican-American NIDDM Parents

Abstract: NIDDM patients with overt fasting hyperglycemia are characterized by multiple defects involving both insulin secretion and insulin action. At this point of the natural history of NIDDM, however, it is difficult to establish which defects are primary and which are acquired secondary to insulinopenia and chronic hyperglycemia. To address this question, we have studied the glucose-tolerant offspring (probands) of two Mexican-American NIDDM parents. Such individuals are at high risk for developing NIDDM later in life. The probands are characterized by hyperinsulinemia in the fasting state and in response to both oral and intravenous glucose. Insulin-mediated glucose disposal (insulin clamp technique), measured at two physiological levels of hyperinsulinemia (approximately 240 and 450 pM [approximately 40 and 75 microU/ml]), was reduced by 43 and 33%, respectively. During both the low- and high-dose insulin clamp steps, impaired nonoxidative glucose disposal, which primarily represents glycogen synthesis, was the major defect responsible for the insulin resistance. During the lower dose insulin clamp step only, a small decrease in glucose oxidation was observed. No defect in suppression of HGP by insulin was demonstrable. The ability of insulin to inhibit lipid oxidation (measured by indirect calorimetry) and plasma FFA concentration was impaired at both levels of hyperinsulinemia. These results indicate that the glucose-tolerant offspring of two NIDDM parents are characterized by hyperinsulinemia and manifest all of the metabolic abnormalities that characterize the fully established diabetic state, including insulin resistance, a major impairment in nonoxidative glucose disposal, a quantitatively less important defect in glucose oxidation, and a diminished insulin-mediated suppression of lipid oxidation and plasma FFA concentration.

The Zucker rat model of obesity, insulin resistance, hyperlipidemia, and renal injury.

Abstract: Although the pathogenesis of obesity in OZR is unknown, the association among hyperinsulinemia, insulin resistance, and hyperlipidemia suggests that investigations using OZR may help define how a number of vascular disease risk factors interact to cause end-organ damage. Like other rat strains, OZR do not develop atherosclerosis spontaneously. Nevertheless, in an endothelial injury model, atherosclerosis was worse in OZR than in LZR. Perhaps more intriguing is the fact that OZR develop spontaneous glomerular injury. Although the mechanisms important in the development and progression of glomerular injury in OZR remain to be clarified, both lipid abnormalities and glomerular hemodynamic alterations could play a role.

Lactate production in adipose tissue : a regulated function with extra-adipose implications

Abstract: Estimates of the quantitative contribution of adipose tissue to whole-body glucose metabolism, previously reported as 1-3%, have been revised to be on the order of 10-30%. These revised estimates come, in part, from a recognition that adipose tissue uses glucose to produce lactate and pyruvate, in addition to CO2 and triglycerides. Lactate production by adipose tissue is modulated in vitro by changes in glucose, insulin, and epinephrine concentrations. In vivo, lactate production is regulated acutely by the animal's nutritional state (fed or fasted) and chronically by the degree of obesity. A strong positive correlation exists between rat fat cell size and relative conversion of glucose to lactate (r = 0.89, P less than 0.001). Diabetes is also associated with markedly increased lactate production in adipocytes. Fat cells from obese or diabetic rats (or humans) can metabolize to lactate as much as 50-70% of the glucose taken up. From these recent studies, a picture is emerging in which the adipose organ may provide lactate for hepatic gluconeogenesis during fasting, and also lactate for hepatic glycogen synthesis after food ingestion. Modulation of adipocyte lactate production and contribution of adipose tissue lactate to the body's fuel economy in physiological and pathological states are the focus of this review.

Diabetes mellitus and macrovascular complications. An epidemiological perspective.

Abstract: It is clearly recognized that patients with NIDDM have an increased risk for CHD. Recent data indicate that persons with glucose concentrations in the nondiabetic range also may be at higher risk for CHD. These associations may not represent cause and effect, however. Emerging data suggest that hyperglycemia and CHD may both arise from hyperinsulinemia/insulin resistance. In support of this hypothesis are studies showing that NIDDM and CHD have many risk factors in common, including age, elevated blood pressure, dyslipidemia, adiposity, and a central pattern of fat distribution. Moreover, these risk factors are frequent concomitants of hyperinsulinemia, itself a risk factor for CHD and perhaps for NIDDM. Although the duration of NIDDM has been infrequently related to risk of CHD, the authors hypothesize that duration of hyperinsulinemia/insulin resistance would be a more sensitive marker for risk of CHD. The relation of IDDM to CHD is a different situation. The etiological process leading to IDDM, namely the destruction of β-cells in genetically predisposed persons, is not related to cardiovascular risk. However, IDDM patients still have an excess of CVD, the risk factors for which may vary according to the location of the diseases (e.g., LEAD vs. CHD). There is a strong relationship between proteinuria and CVD, which has led to a general theory of vascular complications in IDDM based on defective heparan sulfate metabolism (Steno hypothesis). Recent evidence challenges parts of this hypothesis, and the possibility is raised that a higher case-fatality rate in a subgroup of patients with both renal and CVD explains part of the renal connection, as does the general worsening of CVD risk factors.

Abnormal sympathetic overactivity evoked by insulin in the skeletal muscle of patients with essential hypertension.

Abstract: The reason why hyperinsulinemia is associated with essential hypertension is not known. To test the hypothesis of a pathophysiologic link mediated by the sympathetic nervous system, we measured the changes in forearm norepinephrine release, by using the forearm perfusion technique in conjunction with the infusion of tritiated NE, in patients with essential hypertension and in normal subjects receiving insulin intravenously (1 mU/kg per min) while maintaining euglycemia. Hyperinsulinemia (50-60 microU/ml in the deep forearm vein) evoked a significant increase in forearm NE release in both groups of subjects. However, the response of hypertensives was threefold greater compared to that of normotensives (2.28 +/- 45 ng.liter-1.min-1 in hypertensives and 0.80 +/- 0.27 ng.liter-1 in normals; P less than 0.01). Forearm glucose uptake rose to 5.1 +/- .7 mg.liter-1.min-1 in response to insulin in hypertensives and to 7.9 +/- 1.3 mg.liter-1.min-1 in normotensives (P less than 0.05). To clarify whether insulin action was due to a direct effect on muscle NE metabolism, in another set of experiments insulin was infused locally into the brachial artery to expose only the forearm tissues to the same insulin levels as in the systemic studies. During local hyperinsulinemia, forearm NE release remained virtually unchanged both in hypertensive and in normal subjects. Furthermore, forearm glucose disposal was activated to a similar extent in both groups (5.0 +/- 0.6 and 5.2 +/- 1.1 mg.liter-1.min-1 in hypertensives and in normals, respectively). These data demonstrate that: (a) insulin evokes an abnormal muscle sympathetic overactivity in essential hypertension which is mediated by mechanisms involving the central nervous system; and (b) insulin resistance associated with hypertension is demonstrable in the skeletal muscle tissue only with systemic insulin administration which produces muscle sympathetic overactivity. The data fit the hypothesis that the sympathetic system mediates the pathophysiologic link between hyperinsulinemia and essential hypertension.