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

Early after lesion of the ventromedial hypothalamus nuclei (VMH), insulin-induced glucose utilization is increased in white adipose tissue (WAT), whereas oxidative and glycolytic muscles are, respectively, normoresponsive or resistant to insulin. Five weeks later, all of the muscles are resistant, whereas WAT returns to normal responsiveness. The aim of this study was to characterize the insulin receptor kinase activity in WAT and muscles 1 and 6 wk after lesion. The number and affinity of insulin receptors were not modified in any of the tissues studied. Autophosphorylation and phosphorylation of an exogenous substrate were similar in oxidative and glycolytic muscles of VMH and control rats both 1 and 6 wk after the lesion. Insulin receptors from WAT of 1-wk VMH rats exhibited a 2.5-fold increase in insulin-stimulated autophosphorylation and phosphorylation. Six weeks after the lesion, both autophosphorylation and phosphorylation returned to normal values. This suggests that insulin receptor tyrosine kinase activity does not play a significant role in the insulin resistance of skeletal muscles but has a crucial role in mediating the variations of insulin action on WAT observed during the development of VMH obesity.
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PMID:Insulin receptor kinase activity in muscles and white adipose tissue during course of VMH obesity. 131 7

We demonstrated previously that high physiological concentrations of free fatty acids (FFA) rapidly decrease insulin binding, degradation, and action in isolated rat hepatocytes. In this study, hepatocytes from lean and obese Sprague-Dawley rats (Alab, Stockholm) were preincubated with or without 0.4 mM oleic acid, and the effect on insulin binding and tyrosine kinase activity was measured. In the absence of exogenous FFA, insulin binding was reduced in hepatocytes from obese compared with lean rats (mean +/- SE reduction 44 +/- 7%, n = 8, P less than 0.01). Furthermore, the inhibitory effect of oleic acid added to hepatocytes from lean rats (n = 8; 40 +/- 9%, P less than 0.01) was not seen in cells from obese rats. Treating obese rats with Etomoxir, a carnitine palmitoyl transferase I inhibitor, increased insulin binding to isolated hepatocytes by 41 +/- 13% (n = 5, P less than 0.05). There was no difference in total binding to partially purified insulin receptors from solubilized hepatocytes from lean and obese rats, whether cells were or were not preincubated with oleic acid. Tyrosine kinase activity of partially purified receptors from basal or insulin-stimulated cells was not affected by either obesity, treatment with Etomoxir, or preincubating the cells with oleic acid. Thus, both obesity and elevated ambient FFA levels are associated with impaired insulin cell surface binding to isolated hepatocytes, possibly through an effect of lipid oxidation on the internalization/recycling of the insulin-receptor complex without any perturbation of the receptor tyrosine kinase activity. The data suggest that the reduced insulin binding to hepatocytes from obese rats is due to elevated ambient FFA levels.
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PMID:Effect of free fatty acids on insulin receptor binding and tyrosine kinase activity in hepatocytes isolated from lean and obese rats. 131 64

Insulin regulates cellular metabolic reactions by its action on the plasma membrane, intracellular enzymes and the nucleus. The first stage in the propagation of the insulin signal is the coupling of insulin to specific receptors at the cell surface. The exact mechanism whereby the transmembrane signalling mechanism (s) results in different insulin-mediated cellular effects is not known. However, the insulin receptor tyrosine kinase, the expression of second messengers, and the action of protein kinase C may, either individually or in combination, mediate some of the insulin effects, such as translocation and activation of glucose transporter proteins. Insulin resistance in clinical conditions such as insulin-dependent diabetes mellitus (IDDM), non-insulin-dependent diabetes mellitus (NIDDM), hypertension and obesity may be acquired to a large extent, and is thus partially reversible. Regulatory factors in insulin sensitivity, such as free fatty acids, counterregulatory hormones and blood glucose level, play an important role in the metabolic control and pathogenesis of insulin resistance in man.
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PMID:Regulation of insulin action at the cellular level. 204 21

The effect of prolonged treatment with acarbose, an inhibitor of alpha-glycosidase, has been studied in mice made obese and hyperinsulinaemic by goldthioglucose. After the onset of obesity, one month after goldthioglucose administration, mice were then treated, with or without a 10% sucrose supplement, for four months with acarbose, added to the diet at 50 mg/100 g food. When mice received a standard diet, acarbose had no effect on body weight, blood glucose or insulin levels. In contrast, in the control obese mice receiving a 10% sucrose-enriched diet, it decreased the body weight gain, and prevented the rise in glycaemia and insulinaemia. Basal (non insulin-stimulated) glucose uptake, which is decreased in isolated soleus muscle from untreated obese mice, returned to normal values under acarbose treatment. However, muscle insulin resistance was not improved in acarbose-treated obese mice at maximal and submaximal effective concentrations, despite a higher insulin binding in muscles of acarbose-treated obese than in control obese animals. Furthermore, insulin receptor autophosphorylation and tyrosine kinase activity were altered similarly in treated and untreated obese mice compared to lean mice.
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PMID:Effect of an alpha-glycosidase inhibitor on experimentally-induced obesity in mice. 215 94

Resistance to insulin consists in a decrease in insulin's biologic action and is manifested mainly by hyperinsulinism. Clinical investigation of insulin resistance states relies on specialized tests, performed both in vitro and in vivo. The hyperinsulinemic-euglycemic clamp is the reference method for quantifying insulin resistance and can differentiate decreased insulin sensitivity and decreased maximal capacity for glucose uptake. Glucose flux measurements, using glucose labelled with stable isotopes, distinguish hepatic and peripheral factors involved in insulin resistance. In vitro studies include investigations for antibodies against insulin and insulin receptors, studies of insulin receptors and their tyrosine kinase activity, and studies of postreceptor cell metabolism. These investigations are especially useful in genetic syndromes of extreme insulin resistance, whose pathophysiology is largely unelucidated, including: insulin resistance syndromes with acanthosis nigricans, obesity-acanthosis nigricans-hyperandrogenism syndrome, lipoatrophic diabetes, leprechaunism, and other syndromes. But insulin resistance also plays a major role in non-insulin-dependent diabetes mellitus, insulin-dependent diabetes mellitus, and various pathological or even physiological endocrine alterations.
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PMID:[Hyperinsulinism syndromes caused by insulin resistance]. 219 May 20

We examined insulin binding, insulin-stimulated autophosphorylation, and phosphorylation of poly(Glu.Na,Tyr)4:1 by liver and skeletal muscle insulin receptor from lean, obese, and obese streptozocin-induced diabetic Zucker rats. Induction of diabetes with streptozocin (30 mg/kg) lowered the lasting insulin level from 11.4 to 3.8 ng/ml, which was not significantly greater than the lean control level. Autophosphorylation and tyrosine kinase activity of liver insulin receptors were increased 70-100% in the obese control group (relative to lean rats), but diabetes reversed this hyperresponsiveness to insulin. In muscle, obesity was associated with a 40-50% decrease in autophosphorylation and tyrosine kinase activity, which was also reversed in the diabetic state. Autophosphorylation and tyrosine kinase activity were significantly correlated in liver and muscle and were also correlated with fasting insulin levels. These data suggest that insulin-receptor tyrosine kinase activity is regulated differently in liver and muscle and that the abnormalities in kinase activity associated with the obese Zucker rat are at least partly secondary to hyperinsulinemia.
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PMID:Effect of streptozocin-induced diabetes on insulin-receptor tyrosine kinase activity in obese Zucker rats. 233 19

Spontaneous hypertensive-corpulent rats (SHR/N-corpulent), homozygous for the corpulent gene (cp/cp), are obese, hyperinsulinemic and exhibit abnormal glucose tolerance and thus represent a model for type II diabetes and obesity. In view of their overall insulin resistance, we examined liver insulin receptor binding and tyrosine kinase activity from corpulent rats and lean littermates fed purified diets containing 54% sucrose or starch for about 12 wk. Specific 125I-insulin binding to crude liver membranes from female corpulent rats fed either starch or sucrose was reduced to approximately 50% of that seen in lean rats (14 vs. 7%). Affinity of insulin receptors was similar in all groups, suggesting that hyperinsulinemic corpulent rats possess fewer hepatic insulin receptors than do lean rats. Using similar numbers of wheat germ agglutinin-agarose (WGA)-purified insulin receptors with similar affinities for insulin, it was found that basal and insulin-stimulated phosphorylation of the synthetic tyrosine-specific kinase substrate poly(Glu, Tyr)4:1 was similar in lean and obese rats fed sucrose or starch. It is suggested that the contribution of the liver to the insulin resistance in obese SHR/N-cp rats probably lies distal to the insulin receptor tyrosine kinase.
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PMID:Liver insulin receptor tyrosine kinase activity in a rat model of type II diabetes mellitus and obesity. 253 93

Obesity is associated with insulin resistance and type II diabetes mellitus. In the present study, we have characterized hepatic insulin receptor function in two animal models of obesity: the Zucker fatty rat (ZFR), a model of genetic obesity with severe hyperinsulinemia, and the Sprague-Dawley rat with dietary obesity, a model of acquired obesity. Zucker fatty rats were also treated with streptozotocin (STZ) in an effort to examine the effects of relative insulin deficiency and hyperglycemia in the setting of obesity. Using wheat germ agglutinin-purified insulin receptor extracted from liver, no significant difference in insulin binding was identified in either model of obesity. beta-Subunit autophosphorylation was significantly decreased in both obese models relative to that in controls (72% in the obese ZFR and 49% in the overfed Sprague-Dawley model). Kinase activity, as measured by phosphorylation of the 1142-1153 synthetic peptide, was also decreased in both models of obesity by 22% and 64%, respectively. In the Zucker rat, STZ treatment led to an 80% increase in receptor concentration and a further 70% increase in beta-subunit autophosphorylation per receptor, whereas tyrosine kinase activity toward substrate was not altered. Since kinase activity is closely linked to autophosphorylation, we determined the fraction of autophosphorylated (activated) receptors vs. non-phosphorylated (inactive) receptors by using antiphosphotyrosine antibody to precipitate receptors bound with [125I]insulin. There was no significant difference in the percentage of activated insulin receptors in the dietary obese, ZFR, or STZ-treated Zucker rat vs. that in the controls. In all models, the percentage of activated receptors ranged from 32-46% of the total receptor pool. These data suggest that in genetic and acquired obesity, autophosphorylation of the beta-subunit is reduced and is a limiting factor in insulin receptor activation. A similar fraction of all receptors appears to undergo some level of autophosphorylation; however, full autophosphorylation and, thus, activation of the receptor do not occur, and this results in a decrease in kinase activity. This block in autophosphorylation may account for significant reductions in insulin receptor kinase function in obesity.
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PMID:Alterations in the hepatic insulin receptor kinase in genetic and acquired obesity in rats. 255 53

The tyrosine kinase activity of the insulin receptor was investigated in skeletal muscle biopsies from insulin-resistant males with obesity or with Type 2 (non-insulin-dependent) diabetic males who were lean or overweight. The kinase activity of the receptor from all three groups of insulin-resistant subjects was 40% less when compared to the activity of lean control subjects. This alteration was present in the absence of changes in the level of the insulin receptor on its insulin binding characteristics. We conclude that the tyrosine kinase activity of the skeletal muscle insulin receptor is defective in obesity and Type 2 diabetes, and that this alteration contributes to the insulin-resistant characteristics of both disorders.
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PMID:Defective insulin receptor tyrosine kinase in human skeletal muscle in obesity and type 2 (non-insulin-dependent) diabetes mellitus. 282 66

Recent studies have led to an enhanced understanding of cellular alterations that may play an important role in the pathophysiology of non-insulin-dependent diabetes mellitus (NIDDM). The insulin receptor links insulin binding at the cell surface to intracellular activation of insulin's effects. This transducer function involves the tyrosine kinase property of the beta-subunit of the receptor. It was found that adipocytes from subjects with NIDDM had a 50 to 80 percent reduction in insulin-stimulated receptor kinase activity compared with their non-diabetic counterparts. This defect was relatively specific for the diabetic state since no decrease was observed in insulin-resistant non-diabetic obese subjects. The reduction in kinase activity was accounted for by changes in the ratio of two pools of receptors, both of which bind insulin but only one of which is capable of tyrosine autophosphorylation and subsequent kinase activation; 43 percent of the receptors from non-diabetic subjects were capable of autophosphorylation compared with only 14 percent in the NIDDM group. A major component of cellular insulin resistance in NIDDM involves the glucose transport system. Exposure of cells to insulin normally results in enhanced glucose transport mediated by translocation of glucose transporters from a low-density microsomal intracellular pool to the plasma membrane. It was found that cells from NIDDM subjects had a marked depletion of glucose transporters in both plasma membranes and low-density microsomes, relative to obese non-diabetic control participants. Obese non-diabetic persons had a normal number of plasma membrane transporters but a reduced number of low-density microsome transporters in the basal state compared with lean control volunteers; insulin induced the translocation of relatively fewer transporters from the low-density microsome to the plasma membrane in the obese subgroups. In addition to the diminished number of glucose transporters, cells from both NIDDM and obese subjects had impaired functional activity of glucose carriers since decreased whole-cell glucose transport rates could not be entirely explained by the magnitude of the decrement in the number of plasma membrane transporters. Thus, impaired glucose transport is due to both a numerical and functional defect in glucose transporters. The cellular content of high-density microsomal transporters was the same in lean and obese control volunteers and NIDDM subjects, suggesting that transporter synthesis is normal and that cellular depletion results from increased protein turnover once transporters leave the high-density microsomal subfraction.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Cellular mechanisms of insulin resistance in non-insulin-dependent (type II) diabetes. 305 97


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