In vivo glucose metabolism in obese and type II diabetic subjects with or without hypertension

Mitochondrial dysfunction and insulin resistance from the outside in: extracellular matrix, the cytoskeleton, and mitochondria

Insulin resistance in skeletal muscle is a prominent feature of obesity and type 2 diabetes. The association between mitochondrial changes and insulin resistance is well known. More recently, there is growing evidence of a relationship between inflammation, extracellular remodeling, and insulin resistance. The intent of this review is to propose a potentially novel mechanism for the development of insulin resistance, focusing on the underappreciated connections among inflammation, extracellular remodeling, cytoskeletal interactions, mitochondrial function, and insulin resistance in human skeletal muscle. Several sources of inflammation, including expansion of adipose tissue resulting in increased lipolysis and alterations in pro- and anti-inflammatory cytokines, contribute to the insulin resistance observed in obesity and type 2 diabetes. In the experimental model of lipid oversupply, an inflammatory response in skeletal muscle leads to altered expression extracellular matrix-related genes as well as nuclear encoded mitochondrial genes. A similar pattern also is observed in "naturally" occurring insulin resistance in muscle of obese nondiabetic individuals and patients with type 2 diabetes mellitus. More recently, alterations in proteins (including α-actinin-2, desmin, proteasomes, and chaperones) involved in muscle structure and function have been observed in insulin-resistant muscle. Some of these cytoskeletal proteins are mechanosignal transducers that allow muscle fibers to sense contractile activity and respond appropriately. The ensuing alterations in expression of genes coding for mitochondrial proteins and cytoskeletal proteins may contribute to the mitochondrial changes observed in insulin-resistant muscle. These changes in turn may lead to a reduction in fat oxidation and an increase in intramyocellular lipid, which contributes to the defects in insulin signaling in insulin resistance.

HOMA-estimated insulin resistance is associated with hypertension in Iranian diabetic and non-diabetic subjects

The relationship between insulin resistance (IR) and essential hypertension (HTN) is controversial. The aim of this study was to determine the association of IR estimated by homeostasis model assessment of insulin resistance (HOMA-IR) and HTN in a large sample of Iranian diabetic and non-diabetic population. A total of 2047 diabetic and non-diabetic individuals with or without HTN, aged 30-75 yrs, who were referred to a university general hospital between November 2004 and April 2007 were included in this study. Demographic data and anthropometric characteristics of participants were recorded. Fasting blood samples were collected, and fasting plasma glucose (FPG), serum creatinine, lipids, insulin, C-peptide and HbA1c were measured. HOMA-IR and HOMA derived Beta-cell function (HOMA-B) were also calculated. Age, sex and waist girth adjusted HOMA-IR values were compared between hypertensive and normotensive subjects. Hypertensive patients had significantly higher HOMA-IR than age-, sex-, and waist girth-adjusted normotensive individuals in both non-diabetic (2.163 +/- 0.08 and 1.75 +/- 0.03, p < 0.001) and diabetic (3.40 +/- 0.10 and 3.07 +/- 0.09, p < 0.05) groups. Multivariate logistic regression analysis showed that after adjustment for age, sex, waist girth, BMI, triglyceride, total cholesterol, FPG, and C-peptide, HOMA-IR was a significant independent predictor of HTN in all subjects (odds ratio = 1.117, CI 95% = 1.026-1.216, p < 0.05) and in diabetic and non-diabetic subjects separately (odds ratio = 1.102, CI 95% = 1.009-1.203, p < 0.05 and odds ratio = 1.328, CI 95% = 1.116-1.580, p < 0.01, respectively). In conclusion, this study showed that IR is associated with HTN in Iranian diabetic and non-diabetic subjects.

Antidiabetic medications in overweight/obese patients with type 2 diabetes: drawbacks of current drugs and potential advantages of incretin-based treatment on body weight

The vast majority of patients with type 2 diabetes are overweight or obese. Lifestyle intervention to lose weight is recommended in most diabetic patients to improve glycaemic control and reduce associated risk factors for microvascular and macrovascular complications. Even modest weight loss can significantly improve glucose homeostasis and lessen cardiometabolic risk factors, although achieving this level of weight reduction remains difficult for many patients. Complicating the matter, many agents used to target hyperglycaemia are associated with weight gain, making management of overweight or obese patients with type 2 diabetes quite challenging. Incretin-based therapies with the new classes of glucagon-like peptide-1 mimetics (e.g. exenatide, liraglutide) and dipeptidyl peptidase 4 (DPP-4) inhibitors (e.g. sitagliptin, vildagliptin) may be of particular value in the treatment of overweight/obese type 2 diabetic patients because of their efficacy in improving glycaemic control and their favourable or neutral effects on body weight. In addition, DPP-4 inhibitors have a low risk for causing hypoglycaemia, undesirable gastrointestinal effects, or other prominent adverse effects that might limit their use. These classes of drugs hold promise for the treatment of type 2 diabetes, alone or in combination with other classes of antidiabetic agents.

The metabolic syndrome is a risk indicator of microvascular and macrovascular complications in diabetes: results from Metascreen, a multicenter diabetes clinic-based survey

OBJECTIVE

We aimed at assessing the degree of association and the predictive power of the metabolic syndrome with regard to clinically detectable complications in patients with diabetes.

RESEARCH DESIGN AND METHODS

Metascreen is a cross-sectional survey of metabolic syndrome and clinically detected diabetes complications performed in 8,497 patients (7,859 with type 2 diabetes and 638 with type 1 diabetes) randomly chosen in 176 diabetes outpatient clinics throughout Italy. The metabolic syndrome was defined according to either the American Heart Association/National Heart, Lung, and Blood Institute (AHA/NHLBI) or the International Diabetes Federation (IDF) diagnostic criteria. Multivariate analyses of the association(s) between either AHA/NHLBI or IDF metabolic syndrome and clinical complications were performed. Receiver-operator characteristic (ROC) curves were constructed to compare the predictive power of the two sets of diagnostic criteria of the metabolic syndrome.

RESULTS

Either definition of the metabolic syndrome was an independent statistical indicator of the presence of nephropathy and neuropathy (P < 0.02-0.01) in type 1 diabetes and of all complications (P < 0.0001), including cardiovascular disease and retinopathy, in type 2 diabetes. For each complication, the ROC curves based on either AHA/NHLBI or IDF metabolic syndrome were similar to each other and to the ROC curves constructed with all continuous traits compounding the metabolic syndrome.

CONCLUSIONS

The metabolic syndrome, defined according to AHA/NHLBI or IDF diagnostic criteria, is an independent clinical indicator and may be involved in the pathogenesis of both macro- and microvascular complications of diabetes.

Palmitate-mediated downregulation of peroxisome proliferator-activated receptor-gamma coactivator 1alpha in skeletal muscle cells involves MEK1/2 and nuclear factor-kappaB activation

The mechanisms by which elevated levels of free fatty acids cause insulin resistance are not well understood. Previous studies have reported that insulin-resistant states are characterized by a reduction in the expression of peroxisome proliferator-activated receptor-gamma coactivator (PGC)-1, a transcriptional activator that promotes oxidative capacity in skeletal muscle cells. However, little is known about the factors responsible for reduced PGC-1 expression. The expression of PGC-1 mRNA levels was assessed in C2C12 skeletal muscle cells exposed to palmitate either in the presence or in the absence of several inhibitors to study the biochemical pathways involved. We report that exposure of C2C12 skeletal muscle cells to 0.75 mmol/l palmitate, but not oleate, reduced PGC-1alpha mRNA levels (66%; P < 0.001), whereas PGC-1beta expression was not affected. Palmitate led to mitogen-activated protein kinase (MAPK)-extracellular signal-related kinase (ERK) 1/2 (MEK1/2) activation. In addition, pharmacological inhibition of this pathway by coincubation of the palmitate-exposed cells with the MEK1/2 inhibitors PD98059 and U0126 prevented the downregulation of PGC-1alpha. Furthermore, nuclear factor-kappaB (NF-kappaB) activation was also involved in palmitate-mediated PGC-1alpha downregulation, since the NF-kappaB inhibitor parthenolide prevented a decrease in PGC-1alpha expression. These findings indicate that palmitate reduces PGC-1alpha expression in skeletal muscle cells through a mechanism involving MAPK-ERK and NF-kappaB activation.

Myocardial glucose utilisation in type II diabetes mellitus patients treated with sulphonylurea drugs

PURPOSE

Chronic sulphonylurea treatment maintains improved glycaemic control through mechanisms other than enhancement of insulin secretion and may act on various organs. The aim of this study was to investigate whether the chronic use of sulphonylurea drugs influences PET measurement of myocardial glucose utilisation (MGU) in type II diabetes mellitus.

METHODS

Forty-two patients with type II diabetes mellitus and 17 control subjects underwent dynamic (18)F-FDG PET to measure MGU during hyperinsulinaemic euglycaemic clamping. Twenty-one patients had been taking sulphonylurea drugs for more than 1 year (SU group), and the other 21 patients were drug naive (non-SU group). The haemoglobin A1c levels in the two patient groups were similar. Glucose disposal rate (GDR) was also determined as a marker of whole-body insulin resistance.

RESULTS

GDR in the SU group (9.01+/-2.53 mg min(-1) kg(-1)) was significantly higher than that in the non-SU group (4.10+/-2.47, p<0.01) and was similar to that in the controls (9.76+/-2.97). MGU in the SU group (7.66+/-3.02 mg min(-1) 100 g(-1)) was significantly higher than that in the non-SU group (5.53+/-2.05, p<0.01) and was similar to that in the controls (7.49+/-2.74).

CONCLUSION

Chronic sulphonylurea treatment influences MGU independent of the degree of glycaemic control. The effect of medication should be kept in mind when measuring and interpreting MGU in patients with type II diabetes mellitus.

The metabolic syndrome and cardiovascular disease

The metabolic syndrome, which is very common in the general population, is defined by the clustering of several classic cardiovascular risk factors, such as type 2 diabetes, hypertension, high triglycerides and low high-density lipoprotein cholesterol (HDL). Central obesity and insulin resistance, which are the two underlying disorders of the syndrome, are further risk factors for cardiovascular disease. Moreover, a panel of novel (non-traditional) risk factors are ancillary features of the metabolic syndrome. They include biomarkers of chronic mild inflammation (e.g. C-reactive protein, CRP), increased oxidant stress (e.g. oxidized low density lipoprotein, LDL), thrombophilia (e.g. plasminogen activator inhibitor-1, PAI-1) and endothelial dysfunction (e.g. E-selectin). Therefore, subjects with the metabolic syndrome are potentially at high risk of developing atherosclerosis and clinical cardiovascular events.In recent years several longitudinal studies have confirmed that subjects with the metabolic syndrome present with atherosclerosis and suffer from myocardial infarction and stroke at rates higher than subjects without the syndrome. The risk of cardiovascular disease (CVD) is particularly high in women with the syndrome and in subjects with pre-existing diabetes, CVD and/or high CRP. However, an increased risk is already present in subjects with a cluster of multiple mild abnormalities. The risk related to the metabolic syndrome is definitely higher when subjects affected are compared to subjects free of any metabolic abnormality.

Lipid infusion decreases the expression of nuclear encoded mitochondrial genes and increases the expression of extracellular matrix genes in human skeletal muscle

The association between elevated plasma free fatty acid (FFA) concentrations and insulin resistance is well known. Although the cause and effect relationship between FFAs and insulin resistance is complex, plasma FFA is negatively correlated with the expression of peroxisome proliferator activated receptor-gamma cofactor-1 (PGC-1) and nuclear encoded mitochondrial genes. To test whether this association is causal, we infused a triglyceride emulsion (or saline as control) into healthy subjects to increase plasma FFA for 48 h followed by muscle biopsies, microarray analysis, quantitative real time PCR, and immunoblots. Lipid infusion increased plasma FFA concentration from 0.48 +/- 0.02 to 1.73 +/- 0.43 mm and decreased insulin-stimulated glucose disposal from 8.82 +/- 0.69 to 6.67 +/- 0.66 mg/kg.min, both with p < 0.05. PGC-1 mRNA, along with mRNAs for a number of nuclear encoded mitochondrial genes, were reduced by lipid infusion (p < 0.05). Microarray analysis also revealed that lipid infusion caused a significant overexpression of extracellular matrix genes and connective tissue growth factor. Quantitative reverse transcription PCR showed that the mRNA expression of collagens and multiple extracellular matrix genes was higher after the lipid infusion (p < 0.05). Immunoblot analysis revealed that lipid infusion also increased the expression of collagens and the connective tissue growth factor protein. These data suggest that an experimental increase in FFAs decreases the expression of PGC-1 and nuclear encoded mitochondrial genes and also increases the expression of extracellular matrix genes in a manner reminiscent of inflammation.

Insulin Resistance and Hypertension

The association between insulin resistance and insulinemia and hypertension is controversial. We examined the relation between insulin resistance and hypertension in 564 non-Hispanic whites (NHW), 505 Hispanics (H), and 413 African Americans (AA) who participated in the Insulin Resistance Atherosclerosis Study (IRAS). Insulin sensitivity was measured with a frequently sampled intravenous glucose tolerance test with minimal model analysis. The prevalence of hypertension was 32.5%, 49.4%, and 32.3% in NHW, AA, and H, respectively ( P <0.001). When subjects without diabetes in all ethnic groups were combined, age, male sex, race (AA), body mass index (BMI), and insulin resistance, but not fasting insulin, were significantly associated with hypertension. When each ethnic group was analyzed separately, insulin resistance was significantly associated with hypertension in NHW and H, but not AA. After excluding subjects taking antihypertensive medications, male sex, BMI, fasting glucose, and insulin resistance, but not fasting insulin, were significant determinants of blood pressure. When the 3 ethnic groups were analyzed separately, insulin resistance was significantly associated with blood pressure in H, but not NHW, or AA. Neither insulin resistance nor fasting insulin was significantly associated with hypertension or blood pressure in subjects with diabetes of the 3 ethnic groups after adjusting for age, sex, BMI, and waist. In conclusion, insulin resistance, but not insulinemia, was related to hypertension and blood pressure in subjects without diabetes, but ethnic differences in these relations appear to exist. Neither insulin resistance nor insulinemia was related to hypertension or blood pressure in patients with type 2 diabetes in the 3 ethnic groups.

Hypertension, insulin, and proinsulin in participants with impaired glucose tolerance

The association of insulin resistance and hyperinsulinemia to blood pressure has remained controversial. We examined the association of insulinemia to hypertension and blood pressure using baseline measurements for participants of the Diabetes Prevention Program (DPP). The DPP is a multicenter randomized controlled trial of 3819 participants with impaired glucose tolerance, and is designed to evaluate interventions for the delay or prevention of type 2 diabetes. The relationship between hypertension and insulinemia is described overall and by ethnicity. The effects of demographics (age and gender), adiposity, and glucose on the relationship are also presented. Asian Americans and African Americans had a similarly high prevalence of hypertension as did whites; American Indians had a lower prevalence of hypertension. Among participants not on antihypertensive medications, systolic blood pressure was significantly (but weakly) correlated with fasting insulin (r=0.12), homeostasis model assessment of insulin resistance (HOMA IR; r=0.13), and fasting proinsulin (r=0.10) when adjusted for age and gender (all, P<0.001). Systolic blood pressure showed similar correlations to fasting insulin in each ethnic group. After further adjustment for body mass index, the association of fasting insulin to systolic and diastolic blood pressures weakened considerably but remained significant (systolic: r=0.06, P=0.002; DBP: r=0.06, P<0.001). We conclude that a weak but significant association between insulin, (and proinsulin and HOMA IR) and blood pressure exists but is largely explained by overall adiposity. This association is similar among ethnicities, with the possible exception of Hispanics. The relation between insulin concentrations and blood pressure explains relatively little of the ethnic differences in hypertensive prevalence.

Predictors of insulin sensitivity in Type 2 diabetes mellitus

AIMS

To identify the independent predictors of insulin sensitivity in Type 2 diabetes, and to establish whether isolated Type 2 diabetes (i.e. diabetes without overweight, dyslipidaemia and hypertension) is a condition of insulin resistance.

METHODS

We examined 45 patients with non-insulin-treated Type 2 diabetes undergoing a 4-h euglycaemic hyperinsulinaemic clamp (20 mU/m2 per min) combined with 3H-3-D-glucose and 14C-U-glucose infusions and indirect calorimetry. We also examined 1366 patients with non-insulin-treated Type 2 diabetes randomly selected among those attending the Diabetes Clinic and in whom insulin resistance was estimated by Homeostasis Model Assessment (HOMA-IR).

RESULTS

In the 45 patients undergoing glucose clamp studies, insulin-mediated total glucose disposal (TGD) was independently and negatively associated with systolic blood pressure (standardized beta coefficient = -0.407, P = 0.003), plasma triglycerides (beta= -0.355, P = 0.007), and HbA1c (beta= -0.350, P = 0.008). The overall variability of TGD explained by these variables was 53%. Overweight diabetic subjects with central fat distribution, hypertension, hypertriglyceridaemia and poor glycometabolic control had insulin-mediated TGD values markedly lower than their lean counterparts without hypertension, with normal triglycerides, and with good glycometabolic control (16 +/- 5 vs. 31 +/- 10 micromol/min per kg lean body mass, P < 0.01). Nevertheless, the latter still were markedly insulin-resistant when compared with sex- and age-matched non-diabetic control subjects (31 +/- 10 vs. 54 +/- 13 micromol/min per kg lean body mass, P < 0.01). In the 1366 Type 2 diabetic patients of the epidemiological study, HOMA-IR value was independently associated with HbA1c (beta = 0.283, P < 0.0001), plasma triglycerides (beta = 0.246, P < 0.0001), body mass index (beta = 0.139, P < 0.001), waist girth (beta = 0.124, P < 0.001) and hypertension (beta = 0.066, P = 0.006).

CONCLUSION

Overweight, central fat distribution, dyslipidaemia, hypertension and poor glycometabolic control are strong independent predictors of insulin resistance in Type 2 diabetes. However, reduced insulin sensitivity can be found even when Type 2 diabetes is isolated and well controlled.

Intracellular partition of plasma glucose disposal in hypertensive and normotensive subjects with type 2 diabetes mellitus

The aim of this study was to ascertain whether the presence of hypertension conveys a more severe degree of insulin resistance in type 2 diabetes mellitus and, if so, which biochemical pathways are involved. We quantitated the rates of total glucose disposal, glycogen synthesis (GS), glycolysis, glucose oxidation, endogenous glucose production, and LOX in the basal state and during a 4-h euglycemic ( approximately 5 mM) hyperinsulinemic ( approximately 300 pM) clamp carried out in combination with a dual-tracer infusion ([(3)H]-3- and [(14)C]-U-D-glucose) and indirect calorimetry in 42 nonobese noninsulin-treated type 2 diabetic subjects (22 hypertensive and 20 normotensive) and 23 nonobese nondiabetic subjects (9 without and 14 with essential hypertension). Compared with normotensive controls, both groups of diabetic subjects were markedly insulin resistant. In the basal state, all glucose fluxes were similar in diabetic subjects with or without hypertension. During insulin infusion, total glucose disposal was significantly reduced in hypertensive diabetic subjects, compared with their normotensive counterparts (18.7 +/- 1.0 vs. 28.6 +/- 3.0 micromol/min.kg lean body mass; P < 0.01). This difference was almost entirely explained by a marked reduction in GS (4.5 +/- 2.0 vs. 12.5 +/- 3.3 micromol/min.kg lean body mass; P < 0.01). Endogenous glucose production was not different in the two diabetic groups during insulin infusion and was significantly higher than in normotensive controls. Lipid oxidation was less suppressed by hyperinsulinemia in hypertensive than in normotensive diabetic subjects (1.46 +/- 0.1 vs. 0.91 +/- 0.1 micromol/min.kg lean body mass; P < 0.01). Glucose fluxes were not significantly different in nondiabetic subjects with essential hypertension and in normotensive diabetic individuals. These results indicate that hypertension markedly aggravates insulin resistance featuring type 2 diabetes mellitus. The molecular defects underlying this phenomenon involve primarily GS.

Is insulin resistance the principal cause of type 2 diabetes?

The data presented from these recent studies raise serious doubt concerning the commonly held view that insulin resistance is the principal cause of type 2 diabetes: first of all they provide evidence that insulin resistance may not be the primary genetic factor for type 2 diabetes; secondly, they demonstrate that at least under certain circumstances insulin resistance is not essential for diabetes to occur, and then finally, they indicate that insulin resistance may not be the predominant factor determining the degree of hyperglycaemia. Although these studies suggest that the role of insulin resistance relative to that of beta-cell dysfunction in the pathogenesis of type 2 diabetes has been generally overestimated, one should not be left with the impression that insulin resistance is not important. It is certainly an important factor in determining the degree of hyperglycaemia or glucose intolerance present at a given level of beta-cell function. The improvement in glycaemic control after weight loss which lessens insulin resistance or after the administration of pharmacologic agents that improve insulin sensitivity clearly argue that insulin resistance is important in this regard. In addition to influencing the severity of glucose intolerance, insulin resistance is probably also important in determining the time of onset of diabetes. It may do this simply by altering the balance between the body's demand for insulin and the ability of the pancreas to provide insulin. It might adversely affect beta-cell function in addition to increasing the demand for insulin. This concept is schematically represented in figure 3. It is well established that beta-cell function normally deteriorates as a function of age [41]. Although the prevalence of type 2 diabetes increases as a function of age, this by itself obviously does not result in diabetes in the great majority of people. In such individuals their insulin sensitivity is sufficient to maintain the balance between the supply and demand for insulin above the threshold for developing diabetes. Theoretically one may postulate three other situations originating with a genetic beta-cell defect: some people may start off life with normal beta-cell function but experience a genetically determined accelerated deterioration; some people may start off life with reduced beta-cell function (e.g. less beta-cell s); still others may start off with reduced beta-cell function and have an accelerated rate of deterioration. In each of the above situations, at any given level of beta-cell function, the degree of insulin resistance present would alter the threshold for developing impaired glucose tolerance and ultimately type 2 diabetes; in other words, the greater the insulin resistance, the lower the threshold, the earlier the onset and the more severe the diabetes will be. It follows therefore that efforts to diminish insulin resistance and to preserve beta-cell function should both be beneficial. Weight loss and increased physical activity, both of which reduceinsulin resistance, have been shown to prevent progression of people with impaired glucose tolerance to diabetes. Whether this is simply due to shifting the balance between insulin requirements and insulin availability or whether it also involves an improvement in beta-cell function and/or prevention of its deterioration remains to be clarified. Furthermore, it is not known whether pharmacologic agents which improve insulin sensitivity have similar effects.

The genetic basis of type 2 diabetes mellitus: impaired insulin secretion versus impaired insulin sensitivity

Despite the fact that it is the prevalent view that insulin resistance is the main genetic factor predisposing to development of type 2 diabetes, review of several lines of evidence in the literature indicates a lack of overwhelming support for this concept. In fact, the literature better supports the case of impaired insulin secretion being the initial and main genetic factor predisposing to type 2 diabetes, especially 1) the studies in people at high risk to subsequently develop type 2 diabetes (discordant monozygotic twins and women with previous gestational diabetes), 2) the studies demonstrating compete alleviation of insulin resistance with weight loss, and 3) the studies finding that people with type 2 diabetes or IGT can have impaired insulin secretion and no insulin resistance compared with well matched NGT subjects. The fact that insulin resistance may be largely an acquired problem in no way lessens its importance in the pathogenesis of type 2 diabetes. Life style changes (exercise, weight reduction) and pharmacological agents (e.g., biguanides and thiazolidendiones) that reduce insulin resistance or increase insulin sensitivity clearly have major beneficial effects (122, 144-146, 153-155).

Insulin resistance in hypertension is associated with body fat rather than blood pressure

The insulin resistance syndrome has been characterized by hypertension, upper body obesity, insulin resistance, hyperinsulinemia, glucose intolerance, and hypertriglyceridemia. Previous studies are inconsistent regarding the relationship between blood pressure and insulin resistance. We therefore compared the metabolic profile in 60 hypertensive subjects (mean+/-SD arterial pressure, 116+/-7 mm Hg) and 60 normotensive subjects (mean arterial pressure, 88+/-5 mm Hg) matched for age, gender, and body mass index. Hypertensives had significantly higher waist-to-hip ratio than normotensives (P=0.002). The groups did not differ in fasting plasma glucose (0.2 mmol/L, P=0.09), insulin (6 pmol/L, P=0.14), insulin sensitivity index (-0.01 micromol x kg(-1) x min(-1) x pmol/L(-1), P=0.7), and suppression of nonesterified fatty acids during a hyperglycemic clamp (1%, P=0.40). There were significant differences in fasting levels of C-peptide (50 pmol/L, P=0.004) and proinsulin (2 pmol/L, P=0.01), 2-hour postload levels of glucose (0.8 mmol/L, P=0.01) and insulin (84 pmol/L, P=0.01) after oral glucose challenge, and hepatic glucose production during the clamp (2.87 micromol x kg(-1) x min(-1), P=0.02). These differences were not significant when controlling for waist-to-hip ratio. Body mass index and waist-to-hip ratio were similarly associated with the insulin sensitivity index in the hypertensive (r=-0.59, P=0.0001 and r=-0.32, P=0.05) and normotensive (r=-0.58, P=0.0001 and r=-0.39, P=0.05) groups. Hypertension per se is not associated with insulin resistance. However, even small increments in both body mass index and waist-to-hip ratio, as often seen in hypertension, may lead to impairment in insulin sensitivity, probably mediated through altered lipid metabolism.

Response of insulin, glucagon, lactate, and nonesterified fatty acids to glucose in visceral obesity with and without NIDDM: relationship to hypertension

Insulin, glucagon, glucose, nonesterified fatty acids (NEFA), and lactate response to oral glucose tolerance test (OGTT, 75 g glucose) and their correlation with mean blood pressure (BP), were studied in 10 normal subjects (N), 25 subjects with abdominal obesity (O), and 9 subjects with abdominal obesity and IGT or non-insulin-dependent diabetes (OD). O and OD patients, as compared to N subjects, showed increased fasting NEFA, lactate, insulin, and glucagon. NEFA area and insulin total and incremental areas were increased in O and OD (P < 0.001 in all instances). Glucagon total areas were increased only in OD (P < 0.01). Lactate total areas were increased in O (P < 0.001) and in OD (P < 0.01), while lactate incremental area was diminished in O and, even more, in OD subjects (P < 0.001 in both instances) and was inversely correlated with the basal level (P < 0.001). In all subjects as a whole, increase in NEFA area was weakly correlated with total and incremental insulinemic areas (P < 0.05) and more strongly correlated with glucagon and lactate areas (P < 0.01). Conversely, the incremental areas of lactate were negatively correlated with total insulin (P < 0.05), NEFA (P < 0.05), and glucagon (P < 0.001) areas. BP was increased in O (103.62 +/- 2.37) and, even more, in OD (109.41 +/- 5.22) compared to that seen in N (92.55 +/- 0.94 mm Hg), with P < 0.01, and was correlated with fasting insulin (P < 0.01) and glucose (P < 0.05) and, even more, with total (P < 0.001) and incremental (P < 0.01) insulin areas and NEFA areas (P < 0.001). Conversely, BP also was negatively correlated with incremental lactate area (P < 0.01) (similarly to insulin and NEFA area). Our data would suggest that in O and OD patients, insulin resistance is associated with elevated NEFA, insulin and glucagon as well as with high BP. since NEFA are inhibitors of Na,K-ATPase, they could contribute to elevate BP through the repression of this enzyme (which we have shown previously to be reduced in adipose tissue of obese subjects and correlated negatively with BP.

Left ventricular diastolic function in hypertension and role of plasma glucose and insulin. Comparison with diabetic heart

BACKGROUND

Experimental production of glucose intolerance has been associated with increased diastolic stiffness of the left ventricle, accompanied by interstitial fibrosis. Because carbohydrate metabolism is altered in hypertension, we undertook the present study to assess the relation of diastolic dysfunction in hypertension to plasma glucose and insulin concentrations. The latter are also affected by obesity. To facilitate this analysis, we studied moderately obese hypertensives. Elucidation of these relations was then sought in diabetic subjects.

METHODS AND RESULTS

Subjects undergoing catheterization for chest pain were included in the study when significant coronary disease was not present. In groups 1 (lean), 2 (obese), 3 (lean hypertensive), and 4 (obese hypertensives), intraventricular pressures and volumes were determined. Fasting plasma glucose, insulin, hemoglobinAIC, and glucose tolerance were assessed. Basal ejection fraction and end-systolic wall stress were normal in the four groups. Chamber stiffness was significantly elevated in the hypertensives and was higher in group 4 than in group 3 (P < .05). Diastolic dysfunction was correlated with fasting blood glucose (r = .69, P < .006) but not with plasma insulin or left ventricular mass. Chamber stiffness was also increased in diabetics, with a larger effect in the obese.

CONCLUSIONS

Hypertension is associated with increased diastolic stiffness of the left ventricle, which is enhanced by moderate obesity, and abnormal carbohydrate metabolism. Experimentally and in humans, hypertension is associated with interstitial fibrosis of mycardium, the presumed basis for the diastolic dysfunction. Chamber stiffness in group 4 hypertensives was similar to that in the lean diabetics but less than that in the obese diabetics. Although the latter exhibited a correlation with plasma hemoglobinAIC, the large rise in stiffness suggests a potential role for growth factors in further alteration of myocardial composition.

Chronic exogenous hyperinsulinaemia does not modify the acute inhibitory effect of insulin on the secretion of very-low-density lipoprotein triacylglycerol and apolipoprotein B in primary cultures of rat hepatocytes

Male Wistar rats were fitted with subcutaneous osmotic mini-pumps that delivered insulin at a constant rate of 0.20 i.u./h for 7 days. This treatment raised the plasma insulin concentration from 31 +/- 4 to 201 +/- 64 micro-i.u./ml. Hepatocytes prepared from the hyperinsulinaemic animals secreted very-low-density lipoprotein (VLDL) triacylglycerol (TAG) at a higher rate (172 +/- 21 microgram per 24 h per mg cell protein) than did those from sham-operated controls (109 +/- 12 microgram per 24 h per mg) (P<0.05). However, chronic exogenous hyperinsulinaemia had no stimulatory effect on the secretion of VLDL apolipoprotein B (apoB) in derived hepatocytes compared with those from the sham-operated controls (2.32 +/- 0.38 compared with 3.09 +/- 0.40 microgram per 24 h per mg). Hepatocytes from the hyperinsulinaemic rats thus secreted larger VLDL particles as evidenced by the increased TAG:apoB ratio (78.4 +/- 13.1 compared with 38.4 +/- 7.6; P<0.05). In hepatocytes from the hyperinsulinaemic rats a larger proportion of the newly synthesized TAG was secreted as VLDL. Hepatocytes from the hyperinsulinaemic and the sham-operated control animals were equally sensitive to the inhibitory effect of insulin added in vitro on the secretion of VLDL TAG. Insulin added in vitro to the culture medium of hepatocytes from hyperinsulinaemic animals significantly decreased the TAG:apoB ratio of the secreted VLDL. This change did not occur in hepatocytes from sham-operated rats. These results suggest that, in vivo, chronic hyperinsulinaemia is not in itself sufficient to desensitize the liver to the acute inhibitory effect of insulin on the secretion of VLDL.

Insulin and hyperaminoacidemia regulate by a different mechanism leucine turnover and oxidation in obesity

Seven normal glucose-tolerant obese subjects [ideal body weight (IBW) = 161%] and 18 controls (IBW = 102%) were studied with the euglycemic insulin clamp (10 and 40 mU.m-2.min-1) technique, [14C]leucine infusion, and indirect calorimetry to examine if the insulin resistance with respect to glucose metabolism extends to amino acid/protein metabolism. In the basal state, total plasma amino acid and leucine concentrations, endogenous leucine flux (ELF), leucine oxidation (LO), and nonoxidative leucine disposal (NOLD) were similar in obese and control subjects. During both low (10 mU.m-2.min-1)- and higher (40 mU.m-2.min-1)-dose insulin clamp studies, insulin-mediated glucose uptake was reduced in obese vs. control subjects (P < 0.01). During the last hour of the higher-dose insulin clamp step, the decrease in total plasma amino acids, branched-chain amino acids, and leucine concentration was impaired in obese vs. control subjects (P < 0.01). However, suppression of ELF and NOLD was similar in both groups. During the low-dose insulin clamp, the decrease in plasma leucine concentration, LO, and ELF all were impaired (P < 0.01). A second study was performed in which the total plasma amino acid concentration was increased two- to threefold in both groups. Under these conditions of low plasma insulin/high amino acid levels, LO and NOLD increased similarly in obese and control subjects. In conclusion, insulin resistance is a common feature of both glucose and protein metabolism in obesity. The defect in protein metabolism is characterized by an impairment of the ability of insulin to inhibit proteolysis; the stimulatory effect of hyperaminoacidemia on protein synthesis is intact in obesity.

Whole-body glucose metabolism in obese patients with type 2 diabetes mellitus: the impact of hypertension and strict blood glucose control

We have examined the impact of hypertension and blood glucose control on insulin sensitivity in obese Type 2 (non-insulin-dependent) diabetic patients. Glucose metabolism in the basal state and in response to insulin was examined using the euglycaemic, hyperinsulinaemic (2 mU kg-1 min-1) clamp technique in combination with 3-[3H]-glucose infusion and indirect calorimetry in 60 obese Type 2 diabetic patients (30 normotensive patients and 30 hypertensive patients on antihypertensive treatment) and 10 obese normotensive control subjects. In the basal state and during hyperinsulinaemia, glucose disposal rates (total, oxidative, and nonoxidative) were similar in Type 2 diabetic patients with or without hypertension (230 +/- 83 vs 270 +/- 114 mg m-2 min-1 (NS), 83 +/- 28 vs 95 +/- 7 mg m-2 min-1 (NS), 148 +/- 70 vs 180 +/- 89 mg m-2 min-1 (NS), treated hypertensive vs normotensive subjects, respectively). However, compared to obese control subjects (403 +/- 65 mg m-2 min-1) both groups of diabetic patients had significantly decreased insulin-stimulated glucose disposal rates (p < 0.005). Even in a subset of Type 2 diabetic patients with long-term (> 6 months) near normal blood glucose control (HbA1c < 6.1%) significant defects were detectable in whole-body glucose and lipid metabolism when compared to control subjects. These results indicate that treated hypertension does not significantly aggravate the insulin insensitivity that is already present in Type 2 diabetes mellitus. Furthermore, Type 2 diabetic patients with long-term good metabolic control continue to demonstrate insulin insensitivity in peripheral tissues.

Additive effects of obesity, hypertension, and type 2 diabetes on insulin resistance

Resistance to insulin-mediated glucose disposal has been previously shown to be increased in association with obesity, high blood pressure, and non-insulin-dependent diabetes mellitus. We initiated the present study to quantify the separate effects of hypertension and non-insulin-dependent diabetes mellitus on insulin resistance in both nonobese and obese subjects. To accomplish this, 88 subjects were divided into the following five experimental groups: normal blood pressure, nonobese (n = 17); normal blood pressure, obese (n = 18); high blood pressure, nonobese (n = 18); high blood pressure, obese (n = 19); and high blood pressure, obese, non-insulin-dependent diabetes mellitus (n = 16). Plasma glucose and insulin concentrations were measured before and after a 75-g oral glucose load. Resistance to insulin-mediated glucose disposal was estimated by determining the steady-state plasma insulin and glucose concentrations during the last 30 minutes of a continuous infusion of somatostatin (5 micrograms/min), exogenous insulin (25 mU/m2 per minute), and glucose (240 mg/m2 per minute). Since the steady-state plasma insulin concentrations are similar in all subjects, the higher the steady-state plasma glucose, the more insulin resistant the individual. Nonobese subjects with normal blood pressure had the lowest plasma glucose and insulin responses and steady-state plasma glucose concentrations, and their values were significantly different from the other four groups. Obese or nonobese subjects with high blood pressure had significantly higher plasma glucose responses and steady-state plasma glucose concentrations than did their respective weight-matched control subjects.(ABSTRACT TRUNCATED AT 250 WORDS)