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Query: UMLS:C0020538 (hypertension)
 170,190 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The spontaneous hypertensive rat is an animal model characterized by a syndrome of hypertension, insulin resistance and hyperinsulinaemia. To elucidate whether in analogy to other insulin resistant animal models an inactivity of the insulin receptor kinase or an alteration of the glucose transporter (GLUT 4) level in the skeletal muscle might contribute to the pathogenesis of insulin resistance we determined insulin receptor kinase activity and GLUT 4 level in the hindlimbs of spontaneous hypertensive rats and normotensive control rats. Normotensive normoinsulinaemic Lewis and Wistar rats were used as insulin sensitive controls, obese Zucker rats were used as an insulin resistant control with known reduced skeletal muscle insulin receptor kinase activity. Binding of 125I-insulin, crosslinking of 125I-B26-insulin, autophosphorylation in vitro with 32P-ATP and phosphorylation of the synthetic substrate Poly (Glu 4: Tyr 1) were performed after partial purification of solubilized receptors on wheat germ agglutinin columns. GLUT 4 levels were determined by Western blotting of subcellular muscle membranes. Insulin receptors from spontaneous hypertensive rats compared to those from Lewis and Wistar rats showed no difference of the binding characteristics or the in vitro auto- and substrate phosphorylation activity of the receptor, while in the Zucker rats the earlier described insulin receptor kinase defect was clearly evident. Western blots of subcellular muscle membrane fractions with antibodies against GLUT 4 revealed no difference in transporter levels. These data suggest that insulin resistance in spontaneous hypertensive rats is caused neither by an insulin receptor inactivity nor by a decreased number of glucose transporters in the skeletal muscle.
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PMID:Normal insulin receptor tyrosine kinase activity and glucose transporter (GLUT 4) levels in the skeletal muscle of hyperinsulinaemic hypertensive rats. 132 60

Hypertension is frequently associated with peripheral insulin resistance. An expanding body of evidence has described aberrant expression of glucose transporters in the insulin resistance associated with diabetes mellitus. Therefore, we have investigated the relative levels of expression and subcellular distribution of four members of the facilitative glucose transporter family in metabolically important tissues from the hypertensive Milan rat. Skeletal muscle is the major site of peripheral glucose disposal; skeletal muscle membranes isolated from hypertensive animals exhibited a profoundly reduced level of GLUT4 protein compared to normotensive control animals This reduction was confined to the intracellular pool which exhibited a 50% lower level of GLUT4. In contrast, adipocytes, the other major site of peripheral glucose disposal, exhibited no change in the levels of expression of either GLUT1 or GLUT4 transporter isoforms. Hepatocytes from hypertensive animals exhibit similar levels of GLUT2 protein to the normotensive controls. Patterns of expression of GLUT1, GLUT3 and GLUT4 as determined by immunoblot analysis were profoundly altered in certain brain regions in the hypertensive state. Given the importance of the GLUT4 isoform in mediating the insulin-stimulated disposal of glucose into peripheral tissues, the observation that muscle exhibits profoundly decreased levels of this transporter has important implications for the insulin-resistance associated with hypertension in these animals.
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PMID:Analysis of the glucose transporter compliment of metabolically important tissues from the Milan hypertensive rat. 759 7

The author summarizes mechanisms by which insulin resistance and compensatory hyperinsulinism are manifested in the clinical picture. He divides the mechanisms into prereceptor, receptor and postreceptor mechanisms. The latter dominate in the population quantitatively and thus also by their impact because they create the so-called 5H syndrome (association of hyperinsulinism with hyperglycaemia (NIDDM), hyperlipoproteinaemia, hypertension, hirsutism and the polycystic ovary syndrome) or the so-called hormonal metabolic syndrome X, lethal tetrad, metabolic syndrome, syndrome of insulin resistance). The term syndrome X does not appear suitable as it is frequently mistaken for coronary X syndrome which probably is also conditioned by hyperinsulinism, for the hormonal metabolic X syndrome and probably also fot the "fragile X syndrome" in genetics. The 5H syndrome is caused by a postreceptor disorder of insulin efficiency for which so far the molecular basis and dominating organ site have not yet been defined adequately. Hyperinsulinism is conceived as an insulin resistance compensating phenomenon. In its development participates, however, in addition to compensatory hypersecretion also impaired insulin utilization (liver, muscles) and an impaired primary secretory response caused probably by a disorder of blood sugar control (glucokinase, GLUT 2). This is suggested by the frequently inadequate response of the blood sugar level, IRI and C-peptide during the oral glucose tolerance test (OGGT). A hyperinsulinaemic response may be encountered when the blood sugar curve is normal, flat, in impaired glucose tolerance and in diabetes. Thus OGGT alone is not suited for the early detection of the 5H syndrome unless concurrently the IRI and C-peptide response is recorded.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:[Clinical manifestations of the insulin resistance syndrome. The hormonal-metabolic syndrome X, the 5H syndrome and their etiopathogenesis]. 772 46

Recent studies have reported that skeletal muscle characteristics are altered in hypertension, insulin resistance, and android obesity. These conditions represent cardiovascular risk factors that are often "clustered" together, and have begun to be recognized as part of a metabolic/cardiovascular syndrome. This paper reviews the evidence correlating skeletal muscle characteristics to cardiovascular risk factors, and outlines the proposed mechanisms for the relationships. Muscle characteristics (e.g., fiber type, capillary density, oxidative capacity, insulin binding, GLUT 4 levels, and glucose uptake) are discussed. Although aerobic training does not appear to alter the ratio of Type I/II fibers, it favorably affects other skeletal muscle characteristics that are mechanistically linked to cardiovascular risk factors. These muscle adaptations are important in understanding how exercise training helps to prevent cardiovascular disease.
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PMID:Skeletal muscle characteristics: relationships to cardiovascular risk factors. 796 29

It is becoming well established that poor fetal and early postnatal growth can have long-term effects on adult health, including susceptibility to non-insulin-dependent diabetes mellitus, cardiovascular disease and hypertension. It is suggested that this results from poor nutrition during early life having permanent effects on the structure and metabolism of certain organs and tissues. In the present study we investigated the effect of a low-protein diet during pregnancy and lactation on adipocyte properties and glucose tolerance. Rat dams were fed on a diet containing either 200 (control) or 80 (low protein) g protein/kg during pregnancy and lactation. In addition cross-fostering techniques were employed to enable a separate evaluation of the prenatal and postnatal periods. All offspring were weaned onto a 200 g protein/kg diet at 21 d of age and then studied at 6 weeks of age. The mothers' protein supply during lactation appeared to be the most critical time window for long-term growth. In contrast, the offspring of mothers fed on a low-protein diet during pregnancy or lactation were significantly more glucose tolerant than controls, suggesting that both time windows can have long-term effects on glucose tolerance. In addition offspring of mothers fed on a low-protein diet during pregnancy or lactation had significantly smaller adipocytes than controls. However the largest reduction in adipocyte size was observed when there was a low-protein diet during both pregnancy and lactation. The amount of insulin receptor present in adipocyte membranes was increased in the three animal groups that had been exposed to the low-protein diets while levels of the insulin responsive glucose transporter (GLUT 4) were similar in adipocyte membranes from all groups.
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PMID:Altered adipocyte properties in the offspring of protein malnourished rats. 929 65

The resistance to insulin (insulin resistance, IR) is a common feature and a possible link between such frequent disorders as non-insulin dependent diabetes mellitus (NIDDM), hypertension and obesity. Pharmacological amelioration of IR and understanding its pathophysiology are therefore essential for successful management of these disorders. In this review, we will discuss the mechanisms of action of thiazolidinediones (TDs), a new family of insulin-sensitizing agents. Experimental studies of various models of IR and an increasing number of clinical studies have shown that TDs normalize a wide range of metabolic abnormalities associated with IR. By improving insulin sensitivity in skeletal muscles, the adipose tissue and hepatocytes, TDs reduce fasting hyperglycaemia and insulinaemia. Furthermore, TDs markedly influence lipid metabolism--they decrease plasma triglyceride, free fatty acid and LDL-cholesterol levels, and increase plasma HDL-cholesterol concentrations. Although TDs do not stimulate insulin secretion, they improve the secretory response of beta cells to insulin secretagogues. TDs act at various levels of glucose and lipid metabolism--ameliorate some defects in the signalling cascade distal to the insulin receptor and improve glucose uptake in insulin-resistant tissues via increased expression of glucose transporters GLUT1 and GLUT4. TDs also activate glycolysis in hepatocytes, oppose intracellular actions of cyclic AMP, and increase intracellular magnesium levels. TDs bind to peroxisome proliferator activating receptors gamma (PPAR gamma), members of the steroid/thyroid hormone nuclear receptor superfamily of transcription factors involved in adipocyte differentiation and glucose and lipid homeostasis. Activation of PPAR gamma results in the expression of adipocyte-specific genes and differentiation of various cell types in mature adipocytes capable of active glucose uptake and energy storage in the form of lipids. Furthermore, TDs inhibit the pathophysiological effects exerted by tumour-necrosis factor (TNF alpha), a cytokine involved in the pathogenesis of IR. These effects are most likely also mediated by stimulation of PPAR gamma. In mature adipocytes, PPAR gamma stimulation inhibits stearoyl-CoA desaturase 1 (SCD1) enzyme activity resulting in a change of cell membrane fatty acid composition. Apart from their metabolic actions, TDs modulate cardiovascular function and morphology independently of the insulin-sensitizing effects. TDs decrease blood pressure in various models of hypertension as well as in hypertensive insulin-resistant patients, and inhibit proliferation, hypertrophy and migration of vascular smooth muscle cells (VSMC) induced by growth factors. These processes are considered to be crucial in the development of vascular remodelling, atherosclerosis and diabetic organ complications. TDs induce vasodilation by blockade of Ca2+ mobilisation from intracellular stores and by inhibition of extracellular calcium uptake via L-channels. Furthermore, TDs interfere with pressor systems (catecholamines, renin-angiotensin system) and enhance endothelium-dependent vasodilation. A key role of TDs effects in vascular remodelling is played by inhibition of the mitogen-activated protein (MAP) kinase pathway. This signalling pathway is important for VSMC growth and migration in response to stimulation with tyrosine-kinase dependent growth factors. In addition to the vasoprotective mechanisms mentioned above, troglitazone, the latest representative of this pharmacological group, possesses antioxidant actions comparable to vitamin E. In summary, TDs have the unique ability to attack mechanisms responsible for metabolic alterations as well as for vascular abnormalities characteristic for IR. Therefore, TDs represent a powerful research tool in attempts to find a common denominator underlying the pathophysiology of the metabolic syndrome X. A recently reported link between MAP kinase signalling pathway and PPAR gamma
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PMID:Thiazolidinediones--tools for the research of metabolic syndrome X. 980 67

Insulin resistance seems to be a metabolic aberration associated with obesity. Impaired insulin action is also central to a cluster of diseases including non-insulin dependent diabetes, hypertension, dyslipidemias and atherosclerosis. Body fat distribution, especially upper body segment obesity is related to insulin-resistance. Glucose uptake is insulin dependent in skeletal muscle and adipose tissue. From a quantitative standpoint, skeletal muscle has the greater impact on whole body glucose economy, therefore the cause of altered insulin sensitivity has been looked for in this tissue. The skeletal muscle is composed of different types of fibers with specific metabolic and circulatory characteristics; type IIB fibers are less insulin-sensitive and their proportion has been related to obesity and insulin resistance. The different factors that may impair insulin action and alter glucose uptake in skeletal muscle are: lower blood flow to muscle, produced by either decreased vasodilation or by increased sympathetic nerve activity; augmented diffusion distance from capillaries to muscle due to a decrease in capillary number or to enlarged muscle cells; decrease of insulin receptors; change in the fatty acid profile of major membrane structural phospholipids; decrease in glucose transporters (GLUT 4) and/or hexokinase; impairment in metabolic routes of glucose in muscle as reduction in glycogen synthase. Also, the high rate of lipolysis present in obesity and in insulin resistance could lead to an impaired glucose oxidation in muscle.
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PMID:[Obesity, insulin resistance and skeletal muscle characteristics]. 1051 36

Insulin resistance has emerged out as a concept linking diabetes mellitus and hypertension. Clinically it is characterized by hyperinsulinemia, hypertension, central obesity, abnormal lipid profile and cardiovascular complications. Insulin resistance is often associated with presence of anti-insulin antibodies and absent or dysfunctional insulin receptors. At molecular level insulin resistance appears to occur at the level of G-protein, kinase activation, glucose carriers (GLUT) and gene expression. Although with advent or research, the molecular mechanisms of insulin resistance are becoming more clear and there is development of new therapeutic agents like insulin sensitizers (thizolidinediones), in clinical practice, as of today, a patient with insulin resistance is looked upon as hypertensive or having diabetes mellitus. Accordingly he is taking either antihypertensives or antidiabetic drugs or both. It is thus essential to look into effects of these agents on insulin sensitivity. In recent years some scattered studies have been conducted to evaluate the effect of various antihypertensives and antidiabetics on insulin sensitivity. An antihypertensive or antidiabetic drug should directly benefit the cardiovascular risk profile of these patients. Although various newer approaches are explored to have a therapeutic benefit in insulin resistance, it is still a long way in the research, when a suitable pharmacological agent with least untoward effects will be available for the treatment of insulin residence.
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PMID:An overview of pathophysiology and treatment of insulin resistance. 1121 69

In the rat, dexamethasone treatment during late pregnancy leads to intrauterine growth retardation and is used as a model of early programming of adult onset disease. The present study investigated whether pre-natal dexamethasone treatment modifies cardiac glucose transporter (GLUT) protein expression in adulthood and identified signalling pathways involved in the response. Dexamethasone (100 microg/kg body wt per day) administered via an osmotic pump to pregnant rats (day 15 to day 21; term=22 to 23 days) reduced fetal weight at day 21 and caused hypertension, hyperinsulinaemia and elevated corticosterone levels in the adult (24-week-old) male offspring. Cardiac GLUT1 protein expression was selectively up-regulated (2.5-fold; P<0.001), in the absence of altered cardiac GLUT4 protein expression, in adult male offspring of dexamethasone-treated dams. Maternal dexamethasone treatment did not influence cardiac GLUT1 protein expression during fetal or early post-natal life. We examined potential regulatory signalling proteins that might mediate up-regulation of cardiac GLUT1 protein expression in adulthood. We observed marked (2.2-fold; P<0.01) activation of Akt/protein kinase B (PKB), together with modest activation of the anti-apoptotic protein kinase C (PKC) isoforms PKC alpha (88%, P<0.05) and PKC epsilon (56%, P<0.05) in hearts of the early-growth-retarded male offspring. These effects were, however, observed in conjunction with up-regulation of cardiac protein expression of PKC beta(1) (191%, P<0.01), PKC beta(2) (49%, P<0.05) and PKC delta (35%; P<0.01), effects that may have adverse consequences. Maternal dexamethasone treatment was without effect on cardiac extracellular signal-related kinase (ERK) 1 or ERK2 activity in adulthood. In conclusion, our data demonstrate an effect of maternal dexamethasone treatment to up-regulate cardiac GLUT1 protein expression in early-growth-retarded, hypertensive, hyperinsulinaemic adult male offspring, an effect observed in conjunction with activation of Akt/PKB.
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PMID:Early growth retardation induced by excessive exposure to glucocorticoids in utero selectively increases cardiac GLUT1 protein expression and Akt/protein kinase B activity in adulthood. 1125 Jun 42

Here we propose that glucose metabolism can be understood on the basis of three concept-derived axioms: (I) A hierarchy exists among the glucose-utilizing organs with the brain served first, followed by muscle and fat. (II) Tissue-specific glucose transporters allocate glucose among organs in order to maintain brain glucose concentrations. (III) Exogenous carbohydrate supply compensates for glucose alterations that can temporarily occur in muscle and fat. Derived from the control theory, the simplest solution of allocating supply to 2 organs, e.g. brain and muscle, is a "fishbone"-structured model. We reviewed the literature, searching for neuroendocrine and metabolic mechanisms that can fulfill control functions in such a model: The tissue-specific glucose transporters are differentially regulated. GLUT 1, carrying glucose across the blood-brain-barrier, is independent of insulin. Instead, this trans-endothelial glucose transporter is rather dependent on potent regulators of blood vessel function like vascular endothelial growth factor - a pituitary counterregulatory hormone. GLUT 4, carrying glucose across the membranes of muscle and fat cells, depends on insulin. Thereby, insulin allocates glucose to muscle and fat. The hypothalamus-pituitary-adrenal (HPA) axis, the sympathetic nervous system (SNS), and vascular endothelial growth factor allocate glucose to the brain. Multiple "sensors" (some of which have only recently been identified as ATP sensitive potassium channels) measure glucose or glucose equivalents at various sites of the body: the ventromedial hypothalamus, the lateral hypothalamus, portal vein, pancreatic beta cell, renal tubule, muscle and adipose tissue. Feedback pathways both from the brain and from muscle and fat are involved in regulating glucose allocation and exogenous glucose supply. The main feedback signal from the brain is found to be glucose, that from muscle and fat appears to be leptin. In fact, the literature search revealed two or more biological mechanisms for the function of each component in the model, finding glucose regulation highly redundant. This review focuses on "brain glucose" control. The concept of glucose allocation presented here challenges the common opinion of "blood glucose" being the main parameter controlled. According to the latter opinion, hyperglycemia in the metabolic syndrome is due to a putative defect located within the closed loop including the beta cell, muscle and fat cells. That traditional view leaves some peculiarities of e.g. the metabolic syndrome unexplained. The concept of glucose allocation, however, would predict that weight gain - with abundance of glucose in muscle and fat - increases feedback to the brain (via hyperleptinemia) which in turn results in HPA-axis and SNS overdrive, impaired insulin secretion, and insulin resistance. HPA-axis overdrive would account for metabolic abnormalities such as central adiposity, hyperglycemia, dyslipidemia, and hypertension, that are well known clinical aspects the metabolic syndrome. This novel viewpoint of "brain glucose" control may shed new light on the pathogenesis of the metabolic syndrome and type 2 diabetes.
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PMID:The neuroendocrine control of glucose allocation. 1214 83


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