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Query: UMLS:C0011860 (type 2 diabetes)
 57,723 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Obesity and NIDDM are clearly linked. The subgroup of abdominal, visceral obesity has been shown to have a particularly close link to the development of diabetes. This is probably due to the marked insulin resistance of that condition. Epidemiological data show a predictive power for the development of NIDDM in both sexes, in signs of insulin resistance, visceral obesity and, in women, hyperandrogenicity. In men a relative hypogonadism may be of importance. Experimental evidence suggests cause-effect relationships between these factors. In both sexes visceral fat may contribute to insulin resistance in the liver and the periphery by excess production of FFA. Hyperandrogenicity in women may also cause insulin resistance, although the reverse sequence of events cannot be excluded. The relative hypogonadism may well contribute to insulin resistance in men, as well as to the accumulation of visceral fat. There are observations of additional endocrine aberrations in visceral obesity, suggesting a central, neuroendocrine disturbance, which might be a primary factor for the pathogenesis of the syndrome.
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PMID:Regional obesity and NIDDM. 824 91

An increased supply of FFAs for oxidation leads to a reduced rate of glucose oxidation and interferes with the inhibitory action of insulin on hepatic glucose production. Available evidence indicates that in humans skeletal muscle is a site for such substrate competition, which involves both pyruvate oxidation and glycogen synthesis. The insulin resistance of obesity is thought to be mostly of metabolic origin, and fully reversible. A reduction in FFA supply by weight reduction can, however, reverse this defect. The insulin resistance associated with NIDDM is thought to be primary, with a strong genetic basis, and partially irreversible. Patients with NIDDM are unable to increase their glucose oxidation normally in response to insulin to meet the energy demands of the body. Increased oxidation of lipids represents a compensatory phenomenon to meet these demands. Therapeutic use of the glucose-FFA cycle to lower blood glucose levels has yielded conflicting results. Studies are in progress to develop agents that inhibit gluconeogenesis by interfering with FFA oxidation. Nicotinic acid derivatives seem to enhance glycogen synthesis acutely by activating glycogen synthetase. Whether these or similar agents can be used to restore impaired glycogen synthesis, the most characteristic genetic defect in NIDDM, cannot be answered until the effect has been proven in chronic studies. The existence of substrate competition between amino acids and glucose, and an intrinsic hypoaminoacidaemic property of amino acids, makes it possible to expand the Randel cycle into a glucose-FFA-amino acid cycle, which integrates control of substrate disposition at the whole body level.
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PMID:Insulin action and substrate competition. 830 11

Plasminogen activator inhibitor 1 (PAI-1) levels are elevated in obese insulin-resistant subjects. However the mechanism underlying increased PAI-1 levels is unknown. To determine the impact of diabetes on PAI-1 levels and its possible relationship to insulin resistance, hyperinsulinemic euglycemic clamp studies were performed in nine lean control subjects, nine non-diabetic obese subjects and eight obese patients with NIDDM. Fasting plasma PAI-1 levels were 4.0 to 4.7 fold higher in the two obese groups than in the control group. During the 40 mU/m2 x min insulin infusion, suppression of FFA concentration was correlated with fasting plasma PAI-1 levels in both obese non-diabetic and obese NIDDM subjects. It is concluded that (1) obesity rather than diabetes itself plays a major role for the increased PAI-1 levels in NIDDM; (2) resistance to the antilipolytic effect of insulin, resulting in increased FFA concentrations, may participate in producing elevated PAI-1 levels in android obese subjects.
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PMID:Are free fatty acids related to plasma plasminogen activator inhibitor 1 in android obesity? 858 88

Insulin resistance is a precursor to and primary cause of Type 2 diabetes mellitus. In addition, insulin resistance is associated with other chronic diseases, including gestational diabetes, cardiovascular disease, and cancer. Resistance to insulin's effects on carbohydrate metabolism include diminished actions of insulin to enhance glucose uptake and suppress endogenous glucose production. This chapter introduces new concepts related to the mechanism by which insulin stimulates glucose utilization in vivo and demonstrates that these processes are mechanistically linked to glucose production. Insulin acts rapidly in vitro to stimulate glucose uptake; in contrast, its effects in vivo are relatively slow in the conscious animal or human subject. The explanation for this difference between in vitro and in vivo dynamics is the delay associated with insulin transport across capillary endothelium of insulin-sensitive tissues (primarily muscle). Also, interstitial insulin is attenuated in concentration compared to plasma insulin at basal as well as under hyperinsulinemic conditions (plasma:interstitial ratio, 3:2). The sluggishness of insulin action and the attenuation in insulin concentration can be explained by a model in which transendothelial insulin transport is restricted and interstitial insulin binds to insulin-sensitive cells, where the hormone is internalized and degraded. Whether insulin transport occurs by a hormone-specific mechanism (i.e., via receptors on endothelial cells) was tested by comparing transport at physiological with pharmacological insulin concentrations-evidence supports a nonspecific mechanism of transport across endothelium (i.e., diffusion or transcytosis). Transendothelial transport alters the in vivo patterns of insulin signaling-biphasic plasma insulin after glucose injection is reflected in a simple, rapid increase in interstitial insulin to an elevated concentration. The time course of insulin's effect to suppress endogenous glucose output is a mirror image of its effect to enhance glucose uptake; however, there is no transendothelial barrier to insulin action at the liver. The similarity in action dynamics at periphery and liver was explained by a mechanism in which insulin crosses into peripheral tissue and alters a "second (blood-borne) signal" that, in turn, suppresses liver glucose production. Of various possible alternative candidates for the second signal, declining plasma free fatty acids appear to signal suppression of glucose production. We have proposed the "single gateway hypothesis" to explain insulin's action on carbohydrate metabolism in vivo: insulin crosses the endothelial boundary in skeletal muscle (to stimulate glucose disposal) and traverses the endothelial barrier in adipose tissue to suppress lipolysis. The declining free fatty acids are proposed to be a major factor in the insulin-mediated decline in glucose output. This mechanism can be contrasted with the classical concept that portal insulin controls the liver directly. Recent evidence supports the concept that, under normal levels of glucagonemia, less than 25% of the suppression of hepatic glucose output by insulin is due to a direct effect of insulin via the portal vein and that most of the effect (approximately 75%) is explained by the indirect single gateway mechanism. These results raise the question of whether hepatic insulin resistance in Type 2 diabetes can be explained by insulin resistance at the adipocyte, which causes a failure of reduction of FFA by insulin, leading to overproduction of glucose by the liver. The possible role of the single gateway mechanism in diabetes is under investigation.
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PMID:New concepts in extracellular signaling for insulin action: the single gateway hypothesis. 923 59

Suppression of endogenous glucose production (EGP) is one of insulin's primary metabolic effects and failure of this action is a major contributor to fasting hyperglycemia of type 2 diabetes mellitus. Classically, insulin was thought to suppress the liver directly, via hyperinsulinemia in the portal vein. Recently, however, we and others have demonstrated that at least part, and possibly most of insulin's action to suppress EGP is normally mediated via an extrahepatic (i.e., indirect) mechanism. We have suggested that this mechanism involves insulin suppression of adipocyte lipolysis, leading to lowered FFA and reduced EGP ("Single Gateway Hypothesis"). Previous studies of the indirect insulin effect from this laboratory were done under conditions of lowered portal glucagon. Because of the possibility that the direct (i.e., portal) effect of insulin may have been underestimated with hypoglucagonemia, these studies examined the relative importance of portal insulin, versus peripheral insulin (administered at one-half the dose to equalize peripheral insulin levels) at four rates of portal glucagon infusion: 0, 0.65 (under-), 1.5 (basal-), and 3.0 ng/kg per min (over-replacement). Portal versus peripheral insulin suppressed steady-state EGP to the same extent (52%), confirming that the primary effect of insulin to suppress EGP is via the peripheral mechanism. This conclusion was maintained regardless of portal glucagonemia, although there was some evidence for an increase in the direct insulin effect at hyperglucagonemia. The indirect effect of insulin is the primary mechanism of steady-state EGP suppression under normal conditions. The direct effect increases with hyperglucagonemia; however, the indirect effect remains predominant even under those conditions.
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PMID:Indirect effect of insulin to suppress endogenous glucose production is dominant, even with hyperglucagonemia. 939 59

Evidence, gained from human studies, is reviewed showing that elevation of plasma FFA levels produce peripheral and probably also hepatic insulin resistance in obese healthy and diabetic subjects. First, plasma FFA levels are elevated in most obese subjects. Second, physiological elevations of plasma FFA inhibit acutely as well as chronically insulin stimulated glucose uptake in a dose dependent fashion. Responsible for this inhibition is a FFA induced defect in insulin stimulated glucose transport and/or phosphorylation which develops after 3-4 hours of raising plasma FFA and a second defect, consisting of inhibition of glycogen synthase, the rate limiting enzyme of glycogen synthesis, which develops after 4-6 hours. FFA induced inhibition of fatty acid oxidation (Randle effect) does not affect insulin stimulated glucose uptake or glycogen synthesis and thus does not cause insulin resistance. Elevated plasma FFA levels also modestly increase insulin suppressed endogenous glucose production (EGP) although this effect has not been found by all investigators. The reasons why it has been difficult to demonstrate unequivocal effects of FFA on EGP include 1) the fact that FFA promote insulin secretion which counteracts its effect on EGP (FFA increase, while insulin decreases EGP); 2) the recognition that FFA induced increase in gluconeogenesis may be compensated by intrahepatic downregulation of EGP (i.e., by a decrease in glycogenolysis). The FFA induced insulin resistance is physiologically important during starvation by preserving carbohydrate for oxidation in the central nervous system and during pregnancy, where the well recognized accelerated starvation pattern provides carbohydrate for the growing fetus. In obesity, however, there is no need to spare carbohydrate and the FFA induced insulin resistance may result in type 2 diabetes and other cardiovascular risk factors.
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PMID:Free fatty acids (FFA), a link between obesity and insulin resistance. 945 Sep 85

The pancreatic beta cell normally maintains a stable balance among insulin secretion, insulin production, and insulin degradation to keep optimal intracellular stores of the hormone. Elevated levels of FFA markedly enhance insulin secretion; however, the effects of FFA on insulin production and intracellular stores remain unclear. In this study, twofold elevation in total circulating FFA effected by infusion of lard oil and heparin into rats for 6 h under normoglycemic conditions resulted in a marked elevation of circulating insulin levels evident after 4 h, and a 30% decrease in pancreatic insulin content after a 6-h infusion in vivo. Adding 125 muM oleate to isolated rat pancreatic islets cultured with 5.6 mM glucose caused a 50% fall in their insulin content over 24 h, coupled with a marked enhancement of basal insulin secretion. Both effects of fatty acid were blocked by somatostatin. In contrast to the stimulatory effects of oleate on insulin secretion, glucose-induced proinsulin biosynthesis was inhibited by oleate up to 24 h, but was unaffected thereafter. This result was in spite of a two- to threefold oleate-induced increase in preproinsulin mRNA levels, underscoring the importance of translational regulation of proinsulin biosynthesis in maintaining beta cell insulin stores. Collectively, these results suggest that chronically elevated FFA contribute to beta cell dysfunction in the pathogenesis of NIDDM by significantly increasing the basal rate of insulin secretion. This increase in turn results in a decrease in the beta cell's intracellular stores that cannot be offset by commensurate FFA induction of proinsulin biosynthesis.
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PMID:Chronic exposure to free fatty acid reduces pancreatic beta cell insulin content by increasing basal insulin secretion that is not compensated for by a corresponding increase in proinsulin biosynthesis translation. 948 80

Insulin Sensitivity Indices for glycemia [ISI(gly)] and blood FFA [ISI(ffa)] can be calculated with the formulas: ISI(gly) = 2/[(INSp x GLYp) + 1], and ISI(ffa) = 2/[(INSp x FFAp) + 1], where INSp, GLYp and FFAp = insulinemic, glycemic, and FFA areas during OGTT (75 g glucose) of the person under study, simplified by considering only data at 0 and 2 h (0-2 h areas), according to WHO criteria or, better, at 0, 1 and 2 h (0-1-2 h areas). Expressed as unit/ volume.h-1, 0-1-2 h area is equal to 1/2 value at 0 min + value at 1 h + 1/2 value at 2 h, while 0-2 h area is equal to value at 0 + value at 2 h. Instead of areas, basal levels can also be used. Basal levels and areas are expressed taking the mean normal value as unit, so that in normal subjects ISI(gly) and ISI(ffa) are always around 1, with maximal variations between 0 and 2. Each laboratory should have its normal reference values for basal levels and OGTT areas. However, reliable mean normal values were selected from literature. Based on meta-analysis of published data, ISI(gly) and ISI(ffa) were reduced in subjects who were overweight and/or IGT and in NIDDM patients and their relatives. Moreover, correlation of ISI(gly) with the euglycemic clamp data was significant. However, it should be stressed that the clamp procedure is performed under artificially induced steady-state whereas ISI(gly) and ISI(ffa) are obtained under rather physiological conditions, with hormonal and metabolic variables unmodified, thus being suitable to assess whole-body insulin sensitivity in the clinical setting.
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PMID:Insulin sensitivity indices calculated from basal and OGTT-induced insulin, glucose, and FFA levels. 956 67

Release of glucose by liver and kidney are both increased in diabetic animals. Although the overall release of glucose into the circulation is increased in humans with diabetes, excessive release of glucose by either their liver or kidney has not as yet been demonstrated. The present experiments were therefore undertaken to assess the relative contributions of hepatic and renal glucose release to the excessive glucose release found in type 2 diabetes. Using a combination of isotopic and balance techniques to determine total systemic glucose release and renal glucose release in postabsorptive type 2 diabetic subjects and age-weight-matched nondiabetic volunteers, their hepatic glucose release was then calculated as the difference between total systemic glucose release and renal glucose release. Renal glucose release was increased nearly 300% in diabetic subjects (321+/-36 vs. 125+/-15 micromol/min, P < 0.001). Hepatic glucose release was increased approximately 30% (P = 0.03), but increments in hepatic and renal glucose release were comparable (2.60+/-0.70 vs. 2.21+/-0.32, micromol.kg-1.min-1, respectively, P = 0.26). Renal glucose uptake was markedly increased in diabetic subjects (353+/-48 vs. 103+/-10 micromol/min, P < 0.001), resulting in net renal glucose uptake in the diabetic subjects (92+/-50 micromol/ min) versus a net output in the nondiabetic subjects (21+/-14 micromol/min, P = 0.043). Renal glucose uptake was inversely correlated with renal FFA uptake (r = -0.51, P < 0.01), which was reduced by approximately 60% in diabetic subjects (10. 9+/-2.7 vs. 27.0+/-3.3 micromol/min, P < 0.002). We conclude that in type 2 diabetes, both liver and kidney contribute to glucose overproduction and that renal glucose uptake is markedly increased. The latter may suppress renal FFA uptake via a glucose-fatty acid cycle and explain the accumulation of glycogen commonly found in the diabetic kidney.
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PMID:Abnormal renal and hepatic glucose metabolism in type 2 diabetes mellitus. 969 Oct 98

Prior to the advent of nuclear magnetic resonance (NMR) spectroscopy, human glucose metabolism was studied through tracer and tissue biopsy methodology. NMR spectroscopy now provides a noninvasive means to monitor metabolic flux and intracellular metabolite concentrations continuously. 13C NMR spectroscopy has shown that muscle glycogen synthesis accounts for the majority of insulin-stimulated muscle glucose uptake in normal volunteers and that defects in this process are chiefly responsible for insulin resistance in type 1 and type 2 diabetes mellitus, as well as in other insulin resistant states (obesity, insulin-resistant offspring of type 2 diabetic parents, elevation of plasma FFA concentrations). Furthermore, using 31P NMR spectroscopy to measure intracellular glucose-6-phosphate, it has been shown that defects in insulin-stimulated glucose transport/phosphorylation activity are primarily responsible for the insulin resistance in these states.
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PMID:Applications of NMR spectroscopy to study muscle glycogen metabolism in man. 1007 78


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