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Query: UMLS:C0028754 (obesity)
 124,988 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Non-insulin-dependent diabetes mellitus (NIDDM) is an important health problem in the black population of southern Africa. Whether the primary cause of NIDDM is insulin secretory dysfunction or peripheral insulin resistance is unknown. In westernised populations it is believed that insulin resistance and hyperinsulinaemia occur in the early stages of disease, followed later by progressive impairment of insulin secretion. However, we suggest that in the southern African black population a decrease in the mass of functioning beta cells is an important event, making these people vulnerable to the deleterious effects of insulin resistance induced by obesity and other factors. These abnormalities are, in turn, associated with insulin receptor down-regulation. An accelerated decline in beta-cell function then follows in susceptible individuals, ultimately producing striking insulinopenia. Insulinopenic NIDDM in black southern Africans may partly explain why this population has a comparatively low incidence of macrovascular complications and also predicts a short-lived therapeutic response to oral sulphonylureas in most patients.
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PMID:Pathogenesis of non-insulin-dependent diabetes mellitus in the black population of southern Africa. 135 91

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.
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PMID:Evidence for distinctive and intrinsic defects in insulin action in polycystic ovary syndrome. 139 98

The metabolic syndrome (syndrome X) is characterised by an association of elevated insulin levels, a tendency to obesity of the android type, a disturbance of lipid metabolism with elevated triglyceride levels and commonly associated hypertension. The underlying common cause of this syndrome appears to be insulin resistance of the skeletal muscles, which is related in particular to the non-oxidative glucose utilization on the part of the muscle. The molecular cause of this syndrome has not been clarified, but a defect in the signal transduction chain between the insulin receptor and glycogen synthase is suspected. Epidemiological studies have shown that the metabolic syndrome may be considered a preliminary stage of manifest type II diabetes. In addition, it appears to play a major role in the development of cardiovascular complications in certain high-risk groups.
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PMID:[Pathophysiologic principles of metabolic syndrome. Consequences for early diagnosis and prevention]. 148 14

Insulin binding to erythrocytes (IB) and serum immunoreactive insulin concentration (IRI) were measured and relationships between these parameters and body mass index (BMI) were investigated in obese children and age matched controls with normal body weight. IRI was increased and IB was decreased significantly in the obese group compared to data of the controls. The decreased IB was due to a decrease in insulin receptor number since it was not accompanied by alteration of half maximal inhibition dose (ID50). Strong negative correlations were found between BMI and IB and between IRI and IB while a positive association was seen between BMI and IRI. These results prove an interrelationship between weight excess, hyperinsulinism and insulin resistance in childhood obesity.
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PMID:[Insulin resistance in childhood obesity]. 152 85

By the term "insulin resistance" we understand the attenuation of insulin-stimulated glucose uptake, which is mainly due to attenuated glycogen synthesis in skeletal muscle and is partially compensated with regard to plasma glucose homeostasis by hyperinsulinemia. Other mechanisms of insulin are either not attenuated or are less so and may contribute via hyperinsulinemia to the prevalence of hypertension, obesity, dyslipoproteinemia and type-II diabetes. At the level of insulin receptors, resistance can be due to muscle-specific, preferential expression of the low-affinity B-isoform of the insulin receptors. In rare cases of extreme resistance, it can also be due to several mutations at the insulin receptor gene or due to insulin-receptor autoantibodies. At the postreceptor level, the translocation and or expression of the insulin-responsive glucose carrier GluT-4 can be down-regulated via the hexosamine pathway by hyperglycemia plus hyperinsulinemia. Furthermore, Glut-4 can be inhibited and/or down-regulated by sustained insulin deficiency, partially via c-AMP-dependent pathways. Additionally, the insulin-induced glycogen synthesis in skeletal muscle can be attenuated by the endogenous peptides amylin and calcitonin-gene-related peptide, and by modulations of endothelial function, perfusion and capillary recruitment in the microcirculation of skeletal muscle. Epidemiological data indicate a genetic predisposition for insulin resistance. However, among the many mechanisms potentially contributing to the complex syndrome of insulin resistance, no specific localization of that predisposition can be proposed at present.
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PMID:[The mechanisms of insulin resistance]. 153 3

Hyperandrogenism and lipid metabolism were shown to be related intimately. Any discussion of the nature of their relationship must include other clinical and metabolic variables such as hyperinsulinemia and UBO. Despite the many correlations among each of these factors, the appropriate sequence in the pathogenesis of these conditions has not been defined. Do conditions that result in insulin resistance (e.g., genetic defects, insulin receptor antibodies, and obesity) also lead to the development of hyperandrogenemia by direct or indirect ovarian stimulation by insulin? Does hyperandrogenism of ovarian or adrenal origin cause abnormal upper body fat distribution, in turn leading to lipid abnormalities and insulin resistance? Regardless of the issue of mechanism of causality, women with hyperandrogenism are thought to be at greater risk for cardiovascular morbidity and mortality than their normoandrogenic counterparts. These women often are obese, hypertensive, and sedentary; ingest diets high in saturated fats; and have glucose intolerance and/or insulin resistance. All these abnormalities are well known independent risk factors for the development of lipid abnormalities and cardiovascular disease. Whether hyperandrogenism is a secondary consequence of any of these or whether it is an independent contributor to lipid aberrations requires future study. Treatment strategies for hyperandrogenic women, however, should not only be directed toward alleviation of the cosmetic problem of hirsutism but also toward the prevention and treatment of cardiovascular morbidity using modalities aimed at eradicating hyperinsulinemia, hypertension, and dyslipidemia. These modalities should include modifications in diet, exercise, and weight in addition to pharmacologic and/or surgical manipulation. Weight reduction will reduce many cardiovascular risk factors. Obesity is easier to target because of the many risk factors that result in it.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Lipid metabolism and hyperandrogenism. 177 28

The effect of okadaic acid, an inhibitor of protein phosphatases-1 and -2A, was studied on glucose transport and metabolism in soleus muscles isolated from lean and insulin-resistant obese mice. In muscles from lean mice, the uptake of 2-deoxyglucose, an index of glucose transport and phosphorylation, was increased by okadaic acid in a concentration-dependent manner. At 5 microM, okadaic acid was as efficient as a maximally effective insulin concentration. Glucose metabolism (glycolysis and glycogen synthesis) was also measured. Whereas glycolysis was stimulated by okadaic acid, glycogen synthesis was unchanged. When okadaic acid and insulin were added together in the incubation medium, the rates of glucose transport, glycolysis, and glycogen synthesis were similar to those obtained with insulin alone, whether maximal or submaximal insulin concentrations were used. Furthermore, okadaic acid did not activate the kinase activity of the insulin receptor studied in an acellular system or in intact muscles. These results indicate that a step in the insulin-induced stimulation of muscle glucose transport involves a serine/threonine phosphorylation event that is regulated by protein phosphatases-1 and/or -2A. In muscles of insulin-resistant obese mice, the absolute values of deoxyglucose uptake stimulated by okadaic acid were lower than in muscles from lean mice. However, the okadaic acid effect, expressed as a fold stimulation, was normal. These observations suggest that in the insulin-resistant state linked to obesity, the serine/threonine phosphorylation event is likely occurring normally, but a defect at the level of the glucose transporter itself would prevent a normal response to insulin or okadaic acid.
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PMID:Effects of okadaic acid, an inhibitor of protein phosphatases-1 and -2A, on glucose transport and metabolism in skeletal muscle. 184 12

Insulin resistance is frequently associated with acanthosis nigricans and hyperandrogenism. In patients with type A insulin resistance, this has been shown to be due to genetic defects in insulin receptor function. However, other patients with a similar clinical syndrome have been reported to have a variant of this syndrome, in which assays of insulin receptor function were normal. We have sequenced a portion of the insulin receptor gene in one such patient, a 29-yr-old woman with obesity and insulin resistance. The patient is heterozygous for a mutation substituting isoleucine for methionine at position 1153. Met1153 is located in the intracellular domain of the receptor near the cluster of tyrosine phosphorylation sites at positions 1158, 1162, and 1163. Studies of the mutant receptor expressed in NIH-3T3 cells demonstrated that the Ile1153-mutation impairs the ability of insulin to stimulate autophosphorylation of solubilized insulin receptors. In addition, the mutation impairs the ability of insulin to stimulate receptor tyrosine kinase activity to phosphorylate an artificial substrate [poly(Glu-Tyr)]. It seems likely that this defect in receptor tyrosine kinase activity explains the defect in the ability of the patient's insulin receptors to mediate insulin action in vivo. Furthermore, this patient provides a paradigm in which genetic factors act in concert with other risk factors, such as obesity, to cause clinically important insulin resistance.
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PMID:A mutation in the tyrosine kinase domain of the insulin receptor associated with insulin resistance in an obese woman. 189 Jan 61

A homeomorphic mathematical model of cell surface insulin receptor regulation is developed. The overall structure of the model is based on molecular mechanisms suggested by in vivo and in vitro experimental evidence from many different cell types. Model parameters correspond to cellular processes which are constrained by known boundry value conditions. As an example, computer simulation results are compared with published data from BC3H-1 myocytes in culture. With appropriate parameter choice, this model is able to simulate data from other cell types. Cellular processes which are explicitly represented in the model include: bound and unbound receptor endocytosis, receptor recycling, intracellular receptor degradation, and state-dependent receptor synthesis. Most of these processes are represented as first-order events. Using more complex representations of the model structure with higher order rate constants or saturable pathways does not qualitatively improve simulation results. Simulations are able to reproduce ligand-induced down and up regulation of receptors as well as the initial spontaneous display of surface insulin receptors. To demonstrate the behavior of our model and illustrate its utility for explaining insulin receptor regulation for a variety of conditions, simulations for which experimental data is unavailable for direct comparison are also shown. We believe the structure of our model is sufficient to explain insulin receptor regulation in a wide variety of cell types. In addition our model may aid in understanding the receptor component of insulin resistance (decreased sensitivity or responsiveness to insulin) seen in pathological states such as obesity and diabetes mellitus. Finally, this model may be applicable to the study of the regulation of other polypeptide hormone receptors.
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PMID:A mathematical model and computer simulation study of insulin receptor regulation. 189 Aug 48

Among the candidate genes that have been reviewed herein, adipsin, calcitonin, cholecystokin, Gi alpha and Gs subunits of G proteins, insulin I and II, and lipoprotein lipase have all been mapped to specific chromosomes in mouse or rat or both. In none of these cases is the chromosomal location syntenic with murine obesity genes db (on chromosome 4), or ob (on chromosome 6). Thus, all of these genes that code for metabolic modulators that are altered in obese animals but not in lean animals can be ruled out as possible loci of the primary genetic defect, at least for the murine models of obesity. In the case of neuropeptide Y, growth hormone, glucose transporter GLUT-4, the insulin receptor, and glyceraldehyde-3-phosphate dehydrogenase, chromosomal mapping has not yet been reported. However, in each of these cases, the evidence available strongly argues against any one of these physiologic modulators as the likely site of the primary defect for any one of the obesity mutations. Rather, in all of these cases, regardless of whether or not the gene has been mapped, the evidence suggests that posttranscriptional and/or post-translational processes are involved in bringing about the specific alterations in level or activity of the protein product that is seen in the obese animal. Often hormonal regulation is invoked as a possible explanation for the changes observed in gene expression. The hormones most commonly identified as having a mediating effect on the particular metabolic pathways involved are insulin and/or the adrenal glucocorticoids. Since in each of the obese mutants, circulating amounts of these hormones are elevated, severely so in the case of insulin, it would not be surprising to find that they influence the levels and activities of many protein products involved in a variety of central nervous system and peripheral metabolic pathways. Glucocorticoids are known to exert direct effects on gene expression; however, with respect to adipsin gene expression, a direct effect has not been found. Furthermore, insulin itself has been considered as a candidate for the genetic lesion in these animals and has been ruled out by chromosomal localization. Thus, while it may certainly prove to be the case that both insulin and glucocorticoids affect these systems in some way, their effects appear to be indirect. The work by Platt and colleagues in transgenic mice provides the first evidence of signal transduction between an obese mutant allele and the promoter sequence for a gene that shows significantly altered expression in the obese animal.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Animal models of obesity: genetic aspects. 189 4


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