A Bizarre Case of Recurrent Hypoglycemia

Introduction: Severe hypoglycemia is extremely rare in non-diabetic subjects and requires thorough evaluation due to its life threatening consequences. Any injuries resulting from medication use, including physical harm, mental harm, or loss of function is defined as adverse drug events (ADEs). Medication errors can occur due to the inappropriate use of medicine in any prescription stage. We hereby present an intriguing case of recurrent hypoglycemia in relation to it. Case presentation: A 65 year-old white male with surgically induced panhypopituitarism on replacement hydrocortisone, levothyroxine and testosterone was transferred to our hospital with recurrent serious hypoglycemic episodes. He was in his usual state of health until about 2 weeks prior to presentation when he became increasingly fatigued. He was found to have severe hypoglycemia with a blood sugar of 20 mg/dl. He was treated for hypoglycemia and was discharged home 2 days later with an increased dose of hydrocortisone and the provisional diagnosis of adrenal crisis. At home, his symptoms of hypoglycemia recurred. He was then referred to our facility where the Endocrinology service was consulted. At admission, his blood sugar was 69 mg/dl, but it rapidly dropped down to 39 mg/dl with confirmatory serum glucose level of 24 mg/dl. He was started on Dextrose 10%. On further inquiry his daughter told us that she had discovered two different medications in one prescription bottle which had been refilled about 2 weeks prior to this hospitalization, coinciding with the onset of symptoms. The bottle in question was supposed to be for hydrocortisone 10 mg tablets, but it contained 2 different tablets with inscription GXL10 and P10. An online search identified tablets as Glucotrol-XL 10 mg and hydrocortisone 10 mg. Urine drug screen (UDS) for sulfonylureas and glinide was positive for Glipizide (203 ng/ml, normal level 0). His blood sugar stabilized with Dextrose and he was safely discharged home. So it was concluded that recurrent hypoglycemia was secondary to inadvertent administration of hypoglycemic agents, Glucotrol-XL 10 mg, likely aggravated by missing doses of hydrocortisone. Discussion: The first report of medication errors was published in 1940. ADEs comprise the largest single category of adverse events experienced by hospitalized patients,accounting for about 19 percent of all injuries. ADEs are associated with increased morbidity and mortality, prolonged hospitalizations, and higher costs of care. Four medications or medication classes were implicated in 67% of hospitalizations: warfarin, insulins, oral antiplatelet agents, and oral hypoglycemic agents. ADEs in the outpatient setting are an important cause of emergency department visits and hospital admissions. This case emphasized the importance of taking a thorough history and focusing on patient safety and quality care in healthcare.

The management of diabetes in everyday life study: Design and methods for a pragmatic randomized controlled trial comparing the effectiveness of text messaging versus health coaching

Background African American patients with uncontrolled diabetes living in medically underserved areas need effective clinic-based interventions to improve self-care behaviors. Text messaging (TM) and health coaching (HC) are among the most promising low-cost population-based approaches, but little is known about their comparative effectiveness in real-world clinical settings. Objective Use a pragmatic randomized controlled trial design to determine the comparative effectiveness of TM and HC with enhanced usual care (EC) in African American adults with uncontrolled diabetes and multiple chronic health conditions. Methods/design The Management of Diabetes in Everyday Life (MODEL) study is randomizing 646 patients (n = 581with anticipated 90% retention) to 3 intervention arms: TM, HC, and EC. Participants are African American adults living in medically underserved areas of the Mid-South, age ≥ 18, with uncontrolled diabetes (A1c ≥ 8), one or more additional chronic conditions, and who have a phone with texting and voicemail capability. Primary outcome measures: the general diet, exercise, and medication adherence subscales of the revised Summary of Diabetes Self-Care Activities questionnaire assessed at one year. Secondary outcomes: diabetes-specific quality of life, primary care engagement, and average blood sugar (A1c). The study will also assess heterogeneity of treatment effects by six key baseline participant characteristics. Conclusions We describe the design and methods of the MODEL study along with design revisions required during implementation in a pragmatic setting. This trial, upon its conclusion, will allow us to compare the effectiveness of two promising low-cost primary care-based strategies for supporting self-care behaviors among African Americans individuals with uncontrolled diabetes. ClinicalTrials.gov registration number: NCT02957513.

Native Oxyntomodulin Has Significant Glucoregulatory Effects Independent of Weight Loss in Obese Humans With and Without Type 2 Diabetes

Oxyntomodulin (OXM), an enteroendocrine hormone, causes appetite suppression, increased energy expenditure, and weight loss in obese humans via activation of GLP-1 and glucagon receptors. However, the effects of OXM on glucose homeostasis remain ill defined. To address this gap, we evaluated the effects of an i.v. infusion of native OXM on insulin secretion rates (ISRs) and glycemic excursion in a graded glucose infusion (GGI) procedure in two separate randomized, placebo (PBO)-controlled, single-dose crossover trials in 12 overweight and obese subjects without diabetes and in 12 obese subjects with type 2 diabetes mellitus (T2DM), using the GLP-1 analog liraglutide (LIRA) as a comparator in T2DM. In both groups, in the GGI, 3.0 pmol/kg/min of OXM significantly increased ISR and blunted glycemic excursion relative to PBO. In T2DM, the effects of OXM were comparable to those of LIRA, including restoration of β-cell glucose responsiveness to that of nonobese subjects without diabetes. Our findings indicate that native OXM significantly augments glucose-dependent insulin secretion acutely in obese subjects with and without diabetes, with effects comparable to pharmacologic GLP-1 receptor activation and independent of weight loss. Native OXM has potential to improve hyperglycemia via complementary and independent induction of insulin secretion and weight loss.

Insulin secretory effect of sitagliptin: assessment with a hyperglycemic clamp combined with a meal challenge

Sitagliptin, a dipeptidyl peptidase-IV inhibitor (DPP-4), sustains activity of the incretin hormones GLP-1 and GIP and improves hyperglycemia in Type 2 diabetes mellitus (T2DM). It has however proven challenging to quantify the effect of sitagliptin on rates of insulin secretion (ISR) during a prandial challenge. The tight feedback governance of ISR by plasma glucose means that in the face of treatment-related lowering of postprandial glycemia, corresponding stimulation of ISR is lessened. We postulated that sustaining a stable level of moderate hyperglycemia before and during a meal challenge (MC) would be a platform that enables greater clarity to assess the effect of sitagliptin on ISR and an approach that could be valuable to evaluate novel targets that increase insulin secretion directly and by augmenting incretins. A hyperglycemic clamp (HGC) at 160 mg/dl was conducted in 12 healthy volunteers (without diabetes) for 6 h; 3 h into the HGC, MC was administered while maintaining stable hyperglycemia of the HGC for an additional 3 h. Modeling of C-peptide response was used to calculate ISR. In crossover design of three periods (sitagliptin twice and placebo once), the effect of sitagliptin vs. placebo on ISR and the reproducibility of the response to sitagliptin were assessed. Sitagliptin increased ISR compared with placebo by 50% and 20% during the HGC alone and the HGC-MC phases, respectively ( P < 0.001 for both). There was an associated significant treatment-based increase in circulating insulin, as well as active levels of GLP-1. Robust reproducibility of the sitagliptin-mediated ISR response was observed; the intraclass correlation value was 0.94. The findings delineate the effect of sitagliptin to stimulate insulin secretion, and these benchmark data also demonstrate that an HGC-MC can be a useful platform for interrogating therapeutic targets that could potentially modulate ISR via direct action on beta-cells as well as by augmenting release or action of incretins.

Linearity of β-cell response across the metabolic spectrum and to pharmacology: insights from a graded glucose infusion-based investigation series

The graded glucose infusion (GGI) examines insulin secretory response patterns to continuously escalating glycemia. The current study series sought to more fully appraise its performance characteristics. Key questions addressed were comparison of the GGI to the hyperglycemic clamp (HGC), comparison of insulin secretory response patterns across three volunteer populations known to differ in β-cell function (healthy nonobese, obese nondiabetic, and type 2 diabetic), and characterization of effects of known insulin secretagogues in the context of a GGI. Insulin secretory response was measured as changes in insulin, C-peptide, insulin secretion rates (ISR), and ratio of ISR to prevailing glucose (ISR/G). The GGI correlated well with the HGC (r = 0.72 for ISR/G, P < 0.01). The insulin secretory response in type 2 diabetes (T2DM) was significantly blunted (P < 0.001), whereas it was significantly increased in obese nondiabetics compared with healthy nonobese (P < 0.001). Finally, robust (P < 0.001 over placebo) pharmacological effects were observed in T2DM and healthy nonobese volunteers. Collectively, the findings of this investigational series bolster confidence that the GGI has solid attributes for assessing insulin secretory response to glucose across populations and pharmacology. Notably, the coupling of insulin secretory response to glycemic changes was distinctly and uniformly linear across populations and in the context of insulin secretagogues. (Clinical Trial Registration Nos. NCT00782418, NCT01055340, NCT01373450).

Sodium-glucose cotransporter 2 inhibitors and cardiovascular outcomes

Type 2 diabetes mellitus (T2DM) is associated with an elevated risk of cardiovascular (CV) morbidity and mortality. Furthermore, many patients with T2DM have comorbidities that are risk factors for CV disease. While intensive glucose control reduces the risk of diabetic microvascular complications, its relationship to CV outcomes remains unclear. Consequently, the management of CV risk factors in patients with T2DM is complex, and factors other than blood glucose must be considered. Sodium-glucose cotransporter 2 (SGLT2) inhibitors, a class of oral glucose-lowering agents, are associated with reductions in blood pressure and body weight, in addition to decreasing hyperglycemia, and therefore have the potential to reduce CV risk in patients with T2DM. The clinical trial results of SGLT2 inhibitors regarding CV safety and outcomes are discussed, including data from the recently published EMPA-REG OUTCOME study. This trial was the first dedicated CV outcomes study to demonstrate that a glucose-lowering agent lowered CV mortality and all-cause mortality, and reduced hospitalization for heart failure in patients with T2DM at high risk of CV events.

Early Clinical Detection of Pharmacologic Response in Insulin Action in a Nondiabetic Insulin-Resistant Population

Background

Insulin resistance heightens the risk for type 2 diabetes mellitus and cardiovascular disease. Amelioration of insulin resistance may reduce this risk. The thiazolidinedone class of insulin sensitizers improves insulin action in individuals with insulin-resistant diabetes and nondiabetic individuals. However, there are few reports on the time of onset of such effects independent of reversal of glucotoxicity.

Objective

The goal of our study was to test whether the thiazolidinedione pioglitazone has prominent early metabolic effects that can be detected in an obese, nondiabetic, insulin-resistant population.

Methods

We conducted a randomized, double-blind, placebo-controlled, parallel-group trial in men with nondiabetic insulin resistance using a hyperinsulinemic euglycemic clamp technique (at low and high doses of insulin at 10 and 40 mU/m²/min, respectively). The patients were given 30 mg daily oral pioglitazone or placebo for 28 days. Patients underwent a baseline clamp before initiation of treatment, and again at 14 and 28 days of treatment.

Results

Compared with placebo, under high-dose hyperinsulinemia, pioglitazone led to significant increases in glucose disposal rates (GDR) of 1.29 mg/kg/min (90% CI, 0.43–2.15; 39%; P=0.008) that were detectable at 2 weeks of treatment and persisted at 4 weeks of treatment. Under low-dose hyperinsulinemia, significant increases in GDR of 0.40 mg/kg/min (90% CI, 0.17–0.62; 95%; P=0.003) were observed at 4 weeks of treatment. These responses were accompanied by robust suppression of free fatty acids under hyperinsulinemic conditions, and by significant increases in circulating basal total adiponectin at 2 and 4 weeks of treatment.

Conclusions

Significant changes in insulin action across multiple insulin-sensitive tissues can be detected within 2 weeks of initiation of insulin-sensitizing therapy with pioglitazone in obese patients with nondiabetic insulin resistance. ClinicalTrials.gov identifier: NCT01115712.

Insulin resistance in the vasculature

Insulin resistance is typically defined as a reduced ability of insulin to induce glucose uptake by target tissues such as fat and skeletal muscle cells. It accompanies several disease states, including obesity, type 2 diabetes, hepatitis C, and polycystic ovary syndrome, and is a primary feature of metabolic syndrome. Outside of its effects on blood glucose levels, insulin resistance is also associated with a 2- to 3-fold increased risk of cardiovascular mortality. In 1996, Alain Baron, Helmut Steinberg, and colleagues demonstrated that insulin resistance is associated with endothelial dysfunction. This seminal observation led to significant advances in our understanding of insulin's action in health and disease.

Screening for coronary artery disease in patients with diabetes

Coronary artery disease (CAD) accounts for a large fraction of the morbidity, mortality, and cost of diabetes. Recognizing this, nearly 10 years ago the American Diabetes Association published a consensus recommendation that clinicians consider a risk factor-guided screening approach to early diagnosis of CAD in both symptomatic and asymptomatic patients. Subsequent clinical trial results have not supported those recommendations. Since the prior consensus statement, newer imaging methods, such as coronary artery calcium scoring and noninvasive angiography with computed tomography (CT) techniques, have come into use. These technologies, which allow quantitation of atherosclerotic burden and can predict risk of cardiac events, might provide an approach to more widespread coronary atherosclerosis screening. However, over this same time interval, there has been recognition of diabetes as a cardiovascular disease (CVD) equivalent, clear demonstration that medical interventions should provide primary and secondary CVD risk reduction in diabetic populations, and suggestive evidence that percutaneous coronary revascularization may not provide additive survival benefit to intensive medical management in patients with stable CAD. This additional evidence raises the question of whether documenting asymptomatic atherosclerosis or ischemia in people with diabetes is warranted. More data addressing this issue will be forthcoming from the BARI 2-D (Bypass Angioplasty Revascularization Investigation 2 Diabetes) trial. Until then, for patients with type 2 diabetes who are asymptomatic for CAD, we recommend that testing for atherosclerosis or ischemia, perhaps with cardiac CT as the initial test, be reserved for those in whom medical treatment goals cannot be met and for selected individuals in whom there is strong clinical suspicion of very-high-risk CAD. Better approaches to identify such individuals based on readily obtained clinical variables are sorely needed.

Adipose tissue production of hepatocyte growth factor contributes to elevated serum HGF in obesity

Serum HGF is elevated in obese individuals. This study examined the contribution of excess adipose tissue to increased circulating HGF levels in obesity. Serum HGF was measured by ELISA before and after weight loss due to bariatric surgery or a 24-h fast. At 6.1 +/- 0.1 mo following surgery, BMI (50.6 +/- 1.6 vs. 35.1 +/- 1.3 kg/m(2); P < 0.0001) and serum HGF were significantly decreased (1,164 +/- 116 vs. 529 +/- 39 pg/ml, P < 0.001). A 24-h fast did not change serum HGF, but serum leptin was significantly reduced (67.7 +/- 7.1 vs. 50.3 +/- 8.3 ng/ml, P = 0.02). HGF secretion in vitro from adipocytes of obese (BMI 40.3 +/- 2.8 kg/m(2)) subjects was significantly greater (80.9 +/- 10.4 vs. 21.5 +/- 4.0 pg/10(5) cells, P = 0.008) than release from adipocytes of lean (BMI 23.3 +/- 1.4 kg/m(2)) subjects. HGF mRNA levels determined by real-time RT-PCR were not different in adipocytes from lean (BMI 24.0 +/- 0.8 kg/m(2)) and obese (45.7 +/- 3.0 kg/m(2)) subjects, but serum HGF was significantly elevated in the obese individuals studied (787 +/- 61 vs. 489 +/- 49 pg/ml, P = 0.001). TNF-alpha (24 h treatment) significantly increased HGF release from subcutaneous adipocytes 23.6 +/- 8.3% over control (P = 0.02). These data suggest that elevated serum HGF in obesity is in part attributable to excess adipose tissue and that this effect can be reversed by reducing adipose tissue mass through weight loss. Increased HGF secretion from adipocytes of obese subjects may be due to posttranscriptional events possibly related to adipocyte size and stimulation by elevated TNF-alpha in the adipose tissue of obese individuals.

Insulin sensitivity is preserved despite disrupted endothelial function

It is well established that endothelial dysfunction and insulin resistance go hand in hand. However, it is unclear whether endothelial dysfunction per se is sufficient to impair insulin-mediated glucose uptake. We have previously reported that 4 wk of administration of the human immunodeficiency virus (HIV)-1 protease inhibitor indinavir to HIV-negative subjects induces endothelial dysfunction. Hence, we hypothesized that indinavir-induced endothelial dysfunction was associated with impaired insulin-mediated glucose disposal. We measured insulin-mediated glucose disposal at the level of the whole body, skeletal muscle, and vasculature by performing hyperinsulinemic euglycemic clamp, and vascular function studies, in a separate group of HIV-negative healthy nonobese subjects (n = 13) before and after 4 wk of daily oral indinavir. Four weeks of indinavir resulted in a 113 +/- 29% (P < 0.01) reduction of endothelium-dependent vasodilation, consistent with our earlier findings. In addition, there was a significant impairment of insulin-mediated vasodilation (101 +/- 14% before indinavir vs. 35 +/- 15% after indinavir; P < 0.05). However, there was no significant change in insulin-mediated glucose disposal at the level of the whole body (8.9 +/- 0.5 before indinavir vs. 8.5 +/- 0.6 mgxkg(-1)xmin(-1) after indinavir; P = 0.4), or skeletal muscle. Furthermore, in a separate group of four HIV-negative healthy nonobese subjects, we found that 4 wk of indinavir has no sustained effect on insulin-stimulated glucose uptake in adipose tissue. Thus our findings indicate that 1) endothelial dysfunction alone is insufficient to impair insulin-mediated glucose disposal, and 2) indinavir-induced endothelial dysfunction is likely due to a direct effect of the drug on the endothelium and is not coupled to the induction of insulin resistance.

Indinavir impairs endothelial function in healthy HIV-negative men

BACKGROUND

Potent antiretroviral treatment has drastically reduced mortality in HIV-infected patients but may accelerate atherosclerotic disease, which could be partially mediated via endothelial dysfunction.

METHODS

In 8 HIV-negative healthy males, leg blood flow responses to intraartery infusions of methacholine chloride (Mch), sodium nitroprusside, and NG-mono-methyl-L-arginine (L-NMMA) were measured before and after 4 weeks of daily oral indinavir. In the same subjects, we also assessed the effect of indinavir on lipids, insulin sensitivity, markers of inflammation, as well as oxidative stress.

RESULTS

After 4 weeks of indinavir, the endothelium-dependent response to methacholine chloride was impaired (195% +/- 38% vs 83% +/- 13%, P < .05), the response to NG-mono-methyl-L-arginine (nitric oxide-dependent tone) was nearly abrogated (-30% +/- 4% vs -1% +/- 11%, P < .05), whereas the endothelium-independent response to sodium nitroprusside remained unchanged. Fasting insulin levels increased from 5.8 +/- 1.2 to 7.0 +/- 1.4 microU/mL (P < .05), and HOMA-IR scores increased from 1.3 +/- 0.3 to 1.6 +/- 0.3 U (P < .05). There were no changes in blood pressure, lipids, markers of inflammation, or oxidative stress.

CONCLUSIONS

Four weeks of the HIV-1 protease inhibitor indinavir, in the absence of HIV-1 infection, causes vascular dysfunction most likely at the level of endothelial nitric oxide production. The vascular dysfunction may be mediated partially by the concomitant induction of insulin resistance but other mechanisms cannot be ruled out.

Obesity and endothelial dysfunction

Obesity is becoming more prevalent in the developed world because of the abundance of food and the decrease of physical activity. Obesity is a risk factor for a host of diseases from arthritis to cardiovascular disease. The precise mechanisms by which obesity promotes cardiovascular disease are not well understood but are likely to include metabolic and inflammatory responses to the increased amount of stored fat. The endothelium plays a pivotal role in maintaining vascular health. Impaired endothelial function is an independent predictor of cardiovascular disease. Most studies of vascular function in obese subjects have demonstrated impaired endothelial function. This impairment of endothelial function becomes obvious early on, long before any vascular abnormalities become clinically relevant and detectable. Better understanding of the mediators of obesity-induced endothelial dysfunction may lead to the identification of new targets for interventions that may prevent or postpone the development of obesity-related cardiovascular disease.

L-carnitine may attenuate free fatty acid-induced endothelial dysfunction

We have recently shown that elevated levels of free fatty acid (FFA) seen in insulin-resistant obese subjects are associated with endothelial dysfunction. L-carnitine, which is required for mitochondrial FFA transport/oxidation, has been reported to improve vascular function in subjects with diabetes and heart disease. Here, we tested the hypothesis that L-carnitine attenuates FFA-induced endothelial dysfunction. We studied leg blood flow (LBF) responses and leg vascular resistance (LVR) to graded intrafemoral artery infusions of the endothelium-dependent vasodilator, methacholine chloride (MCh). A group (n = 7) of normal lean subjects was studied under basal conditions (saline), after 2 h of FFA elevation (FFA), and then after 2 h of superimposing L-carnitine on FFA elevation. FFA elevation caused the maximal LBF increment in response to MCh to decrease from 0.388 +/- 0.08 to 0.212 +/- 0.071 L/min (P < 0.05). Similarly, FFA blunted the maximum decrease in LVR in response to MCh from -315 +/- 41 U to -105 +/- 46 U (P < 0.05). The superimposed L-carnitine restored the LBF increment in response to MCh to 0.488 +/- 0.088 L/min (P < 0.05 vs. FFA) and the maximum fall in LVR to -287 +/- 75 U (P < 0.05 vs. FFA), indicating that L-carnitine elevation may attenuate FFA-induced endothelial dysfunction. In conclusion, our data suggest that increasing L-carnitine levels may improve FFA-induced and obesity-associated endothelial dysfunction. This improved endothelial function may delay or prevent the development of excess cardiovascular disease.

FFAs: do they play a role in vascular disease in the insulin resistance syndrome?

The insulin resistance syndrome, otherwise known as the metabolic syndrome, describes a cluster of cardiovascular and metabolic abnormalities, which are strongly associated with overweight and obesity. The importance of the syndrome is due to its increased rates of cardiovascular morbidity and mortality. Insulin resistance is also characterized by elevated free fatty acid (FFA) levels. In otherwise healthy human subjects, elevation of FFA impairs endothelial function. This appears to be largely the result of blunting of nitric oxide-dependent tone, most likely at the level of the endothelial isoform of nitric oxide synthase (eNOS). Some of the potential mediatory mechanisms include oxidative stress, proinflammatory cytokines, C-reactive protein, or endogenous inhibitors of eNOS. Regardless of the mechanism(s) that mediates the effects of increased FFA on the vasculature, impaired vascular function is likely to account, at least in part, for the increase in cardiovascular mortality in subjects with the insulin resistance syndrome.

Interactions between endothelin and nitric oxide in the regulation of vascular tone in obesity and diabetes

Endothelial dysfunction reflects an imbalance of vasodilators and vasoconstrictors. Endogenous endothelin activity seems to be increased in human obesity and type 2 diabetes, and cellular studies suggest that this factor may itself reduce bioavailable nitric oxide (NO). We studied 20 lean, 20 obese, and 14 type 2 diabetic individuals under three protocols, measuring leg vascular responses to intra-arterial infusions of NG-monomethyl-l-arginine (l-NMMA; an inhibitor of NO synthase) alone or in combination with BQ123 (an antagonist of type A endothelin receptors) or phentolamine (used as a control vasodilator). NO synthase inhibition alone (study 1) produced an approximately 40% increase in leg vascular resistance (LVR) in all three participant groups, which was not statistically different across groups (increase in LVR: lean, 135 +/- 28; obese, 140 +/- 32; type 2 diabetic, 184 +/- 51 units; NS). By design, BQ123 at the infused rate of 3 micromol/min produced equivalent approximately 35% reductions in LVR across groups. The subsequent addition of l-NMMA produced a greater increase in LVR among obese participants than lean or type 2 diabetic participants (study 2: lean, 182 +/- 48; obese, 311 +/- 66; type 2 diabetic, 186 +/- 40; P = 0.07). Compared with study 1, the effect of l-NMMA was magnified by BQ123 in obese participants but not in lean or type 2 diabetic participants (P = 0.005, study 1 vs. 2; P = 0.03 for group effect). Phentolamine (75 mg/min) produced vasodilation in obese participants comparable to that seen with BQ123 but failed to augment the L-NMMA response. Endothelin antagonism unmasks or augments NO synthesis capacity in obese but not type 2 diabetic participants. This suggests that impaired NO bioavailability as a result of endogenous endothelin may contribute to endothelial dysfunction in obesity, in addition to direct vasoconstrictor effects of endothelin. In contrast, endothelin antagonism alone is insufficient to restore impaired NO bioavailability in diabetes.

Women and Heart Disease

Cardiovascular disease (CVD) is the primary cause of death in women, and women with type 2 diabetes mellitus are at greater risk of CVD compared with nondiabetic women. The increment in risk attributable to diabetes is greater in women than in men. The extent to which hyperglycemia contributes to heart disease risk has been examined in observational studies and clinical trials, although most included only men or did not analyze sex differences. The probable adverse influence of hyperglycemia is potentially mediated by impaired endothelial function, and/or by other mechanisms. Beyond high blood glucose level, a number of other common risk factors for CVD, including hypertension, dyslipidemia, and cigarette smoking, are seen in women with diabetes and require special attention. Presentation and diagnosis of CVD may differ between women and men, regardless of the presence of diabetes. Recognizing the potential for atypical presentation of CVD in women and the limitations of common diagnostic tools are important in preventing unnecessary delay in initiating proper treatment. Based on what we know today, treatment of CVD should be at least as aggressive in women-and especially in those with diabetes-as it is in men. Future trials should generate specific data on CVD in women, either by design of female-only studies or by subgroup analysis by sex.

Coupling of metabolism and cardiovascular response represents normal physiology

In this issue of Clinical Science, Fugmann and co-workers demonstrate a highly integrated cardiovascular response to changes in plasma concentrations of glucose, triacylglycerols (triglycerides), fatty acids and insulin. Since the different substrates, alone and combined, evoked these changes, this response is likely to be a physiological one and directed towards minimizing the extent and duration of substrate elevations that could cause vascular dysfunction.

Troglitazone therapy improves endothelial function to near normal levels in women with polycystic ovary syndrome

Obese women with polycystic ovary syndrome (PCOS) exhibit impaired endothelial function, which is strongly and directly correlated with both testosterone levels and insulin resistance. Endothelial dysfunction is considered a potent risk factor for macrovascular disease. Because troglitazone (Tgz) improves both hormonal profiles and insulin sensitivity, we tested whether Tgz treatment ameliorates endothelial function in these patients. We studied leg blood flow (LBF) responses to graded intrafemoral artery infusion of the endothelium-dependent vasodilator methacholine chloride (MCh) and to a 4-h hyperinsulinemic euglycemic clamp (120 mU/m(2) x min) in 10 PCOS, before and after 3 months treatment with Tgz (600 mg/d). A group of 13 obese women (OBW) matched for age, weight, body fat (>40% in both groups), blood pressure, and total cholesterol served as controls. PCOS patients exhibited elevated free testosterone (fT) and triglycerides (TG) and lower high density lipoprotein cholesterol levels compared with OBW [14.0 +/- 1.0 vs. 3.7 +/- 0.6 pmol/liter (P < 0.0001), 1.60 +/- 0.28 vs. 0.94 +/- 0.09 mmol/liter (P < 0.02), and 0.91 +/- 0.04 vs. 1.1 +/- 0.04 mmol/liter (P < 0.005), respectively]. Tgz treatment reduced fT levels, but did not improve the TG and high density lipoprotein profile [to 9.7 +/- 2.8 pmol/liter (P < 0.007), 1.49 +/- 0.34 mmol/liter (P = NS), and 0.93 +/- 0.07 mmol/liter (P = NS), respectively]. Basal LBF was unchanged after Tgz. In PCOS compared with OBW, insulin stimulated glucose disposal (52.7 +/- 6.6 vs. 85.5 +/- 4.4 micromol/kg fat-free mass x min; P < 0.0005) and vasodilation (increase in LBF, 22 +/- 14% vs. 59 +/- 15%; P < 0.05) were significantly improved after Tgz treatment to 68.8 +/- 7.2 micromol/kg fat-free mass x min (P < 0.0001) and 101 +/- 48% (P < 0.03), respectively. The increase in LBF in response to MCh in PCOS was markedly more pronounced after treatment (P < 0.01, by ANOVA) and was similar to that observed in OBW. Before Tgz treatment, maximal LBF increments in response to MCh were 130 +/- 25% and 233 +/- 29% in PCOS and OBW, respectively (P < 0.01). After Tgz treatment, PCOS values improved, achieving increments similar to those in OBW (245 +/- 45%; P < 0.04). Tgz treatment in PCOS improves both hormonal and metabolic features. These modifications are associated with improvement of endothelial function, suggesting that Tgz could be a useful tool to reduce the risk of macrovascular disease in women with PCOS and perhaps in other insulin-resistant syndromes.

Endothelin contributes to basal vascular tone and endothelial dysfunction in human obesity and type 2 diabetes

Endothelium-dependent vasodilation is impaired in clinical states of insulin resistance such as obesity and type 2 diabetes. Individuals who have hyperinsulinemic insulin resistance have relatively elevated circulating levels of endothelin (ET)-1, suggesting that ET-1 may be important in the endothelial dysfunction and alterations of vascular tone in these conditions. In 8 lean subjects, 12 nondiabetic obese subjects, and 8 subjects with type 2 diabetes, we measured basal and methacholine-stimulated rates of leg blood flow (LBF) and total serum nitrates (NOx) before and after the intrafemoral arterial administration of BQ123, a specific blocker of ET(A) receptors. BQ123 produced significant vasodilation in the obese and type 2 diabetic subjects (leg vascular resistance = mean arterial pressure/LBF fell by 34 and 36%; P < 0.005) but not in the lean subjects (13%; P = NS, P = 0.018 comparing all groups). ET(A) blockade did not change basal NOx flux (NOx*LBF). This suggests increased basal ET-1 constrictor tone among obese and type 2 diabetic subjects. BQ123 corrected the baseline defect in endothelium-dependent vasodilation seen in obese and type 2 diabetic subjects, suggesting an important contribution of ET-1 to endothelial dysfunction in these subjects. In contrast to basal conditions, stimulated NOx flux was augmented by BQ123 in obese and type 2 diabetic subjects but not in L subjects (P = 0.04), suggesting a combined effect of ET(A) blockade to reduce constrictor tone and augment dilator tone. Endothelin seems to contribute to endothelial dysfunction and the regulation of vascular tone in human obesity and type 2 diabetes.

Hyperglycemic clamp assessment of insulin secretory responses in normal subjects treated with olanzapine, risperidone, or placebo

The goal of this study was to evaluate the effect of olanzapine or risperidone treatment on beta-cell function in healthy volunteers. Subjects were randomly assigned to single-blind therapy with olanzapine (10 mg/d; n = 17), risperidone (4 mg/d; n = 13), or placebo (n = 18) for 15-17 d. Insulin secretion was quantitatively assessed at baseline and the end of the study period using the hyperglycemic clamp. Weight increased significantly (P < 0.01) in the olanzapine (2.8 +/- 1.7 kg) and risperidone (3.1 +/- 2.1 kg) treatment groups. An increase ( approximately 25%) in the insulin response to hyperglycemia and a decrease ( approximately 18%) in the insulin sensitivity index were observed after treatment with olanzapine and risperidone. The change in insulin response was correlated (r = 0.5576; P = 0.019) with a change in body mass index. When the impact of weight change was accounted for by multivariate regression analyses, no significant change in insulin response or insulin sensitivity was detected after treatment with olanzapine or risperidone. We found no evidence that treatment of healthy volunteers with olanzapine or risperidone decreased the insulin secretory response to a prolonged hyperglycemic challenge. The results of this study do not support the hypothesis that olanzapine or risperidone directly impair pancreatic beta-cell function.

Vascular function, insulin resistance and fatty acids

Over the past 10 years it has become clear that intact vascular function, especially at the level of the endothelium, is paramount in the prevention or delay of cardiovascular disease. It has also become clear that insulin itself, in addition to its metabolic actions, directly effects vascular endothelium and smooth muscle. Insulin, at normal physiologic concentrations, causes changes in skeletal muscle blood flow in healthy, insulin-sensitive subjects. Insulin's effect on the endothelium is mediated through its own receptor and insulin signalling pathways, resulting in the increased release of nitric oxide. Insulin's vascular actions are impaired in insulin-resistant conditions such as obesity, Type II (non-insulin-dependent) diabetes mellitus and hypertension, which could contribute to the excessive rates of cardiovascular disease in these groups. Insulin-resistant states of obesity and Type II diabetes show a multitude of metabolic abnormalities that could cause vascular dysfunction. Non-esterified fatty acid levels increase long before hyperglycaemia becomes present. Raised non-esterified fatty acids impair insulin's effect on glucose uptake in skeletal muscle and the vascular endothelium and thus could have detrimental effects on the vasculature, leading to premature cardiovascular disease.

Role of amylin in insulin secretion and action in humans: antagonist studies across the spectrum of insulin sensitivity

BACKGROUND

Amylin is a peptide co-secreted with insulin by pancreatic beta-cells. A role for amylin in the pathogenesis of type 2 diabetes mellitus (DM2) has been suggested by in vitro and in vivo studies indicating an effect of amylin to cause insulin resistance and/or inhibit insulin secretion.

METHODS

We have determined the effect of endogenous amylin on insulin secretion and insulin action in humans by performing 4-h hyperglycemic clamps during infusion of placebo or a specific amylin receptor antagonist (ARA) in paired, double-blinded, crossover studies. We studied nine healthy lean, ten healthy obese (BMI>27) and ten obesity-matched DM2 subjects.

RESULTS

Infusion of ARA alone had no effect on basal insulin, glucose or glucose turnover in any group. Under combined hyperglycemia and ARA infusion, lean subjects displayed a 32% augmentation in insulin levels [AUC 33,565+/-3556 (placebo) to 44,562+/-1379 (ARA) pmol/l/min, p<0.01]. The concomitant increase in glucose disposal rate (GDR) was proportionate, indicating no change in insulin sensitivity (ISI 27.7+/-2.7 vs 27.3+/-2.1, p=NS). In obese subjects, basal insulin and the rise in insulin during the clamp were greater (AUC I 44% increase from 82,054+/-15 407 to 117,922+/-27,085, p<0.01), and also accompanied by a proportionate rise in GDR reflecting an unchanged insulin sensitivity (ISI 12.1+/-2.9 vs 10.8+/-3.0, p=NS). In lean and obese subjects, the C-peptide response to hyperglycemia was also augmented by ARA (p=0.007). No effect of ARA on insulin secretion or action was observed in diabetic subjects.

CONCLUSIONS

The present data are consistent with an effect of endogenous amylin on the beta-cell to modulate and/or restrain insulin secretion, and indicate that endogenous amylin does not affect insulin action. These observations provide the first human evidence that amylin plays a role in the modulation of insulin secretion.

Repeatability characteristics of simple indices of insulin resistance: implications for research applications

The objectives of this study were to evaluate test characteristics, such as normality of distribution, variation, and repeatability, of simple fasting measures of insulin sensitivity and to use the results to choose among these measures. Duplicate fasting samples of insulin and glucose were collected before 4 h of euglycemic hyperinsulinemic clamping using insulin infusion rates ranging from 40-600 mU/m2 x min. Currently recommended estimates of insulin sensitivity, including the fasting insulin, 40/insulin, the homeostasis model assessment, the logarithmic transformation of the homeostasis model assessment, and the Quantitative Insulin Sensitivity Check Index, were evaluated. The normality of distribution and the variability of the tests (coefficient of variation and discriminant ratio) were compared between the measures and against the "gold standard" hyperinsulinemic clamp. Data from 253 clamp studies in 152 subjects were examined, including 79 repeated studies for repeatability analysis. In subjects ranging from lean to diabetic, the log transformed fasting measures combining insulin and glucose had normal distributions and test characteristics superior to the other simple indices (logarithmic transformation of the homeostasis model assessment coefficient of variation, 0.55; discriminant ratio, 13; Quantitative Insulin Sensitivity Check Index coefficient of variation, 0.05; discriminant ratio, 10) and statistically comparable to euglycemic hyperinsulinemic clamps (coefficient of variation, 0.10; discriminant ratio, 6.4). These favorable characteristics helped explain the superior correlations of these measures with the hyperinsulinemic clamps among insulin-resistant subjects. Furthermore, therapeutic changes in insulin sensitivity were as readily demonstrated with these simple measures as with the hyperinsulinemic clamp. The test characteristics of the logarithmic transformation of the homeostasis model assessment and the Quantitative Insulin Sensitivity Check Index are superior to other simple indices of insulin sensitivity. This helps explain their excellent correlations with formal measures both at baseline and with changes in insulin sensitivity and supports their broader application in clinical research.

Polycystic ovary syndrome is associated with endothelial dysfunction

BACKGROUND

We recently reported endothelial dysfunction as a novel cardiovascular risk factor associated with insulin resistance/obesity. Here, we tested whether hyperandrogenic insulin-resistant women with polycystic ovary syndrome (PCOS) who are at increased risk of macrovascular disease display impaired endothelium-dependent vasodilation and whether endothelial function in PCOS is associated with particular metabolic and/or hormonal characteristics.

METHODS AND RESULTS

We studied leg blood flow (LBF) responses to graded intrafemoral artery infusions of the endothelium-dependent vasodilator methacholine chloride (MCh) and to euglycemic hyperinsulinemia in 12 obese women with PCOS and in 13 healthy age- and weight-matched control subjects (OBW). LBF increments in response to MCh were 50% lower in the PCOS group than in the OBW group (P:<0.01). Euglycemic hyperinsulinemia increased LBF above baseline by 30% in the PCOS and 60% in OBW group (P:<0.05 between groups). Across all subjects, the maximal LBF response to MCh exhibited a strong inverse correlation with free testosterone levels (r=-0.52, P:<0.007). This relationship was stronger than with any other parameter, including insulin sensitivity.

CONCLUSIONS

PCOS is characterized by (1) endothelial dysfunction and (2) resistance to the vasodilating action of insulin. This endothelial dysfunction appears to be associated with both elevated androgen levels and insulin resistance. Given the central vasoprotective role of endothelium, these findings could explain, at least in part, the increased risk for macrovascular disease in women with PCOS.

Free fatty acid elevation impairs insulin-mediated vasodilation and nitric oxide production

The effect and time course of free fatty acid (FFA) elevation on insulin-mediated vasodilation (IMV) and the relationship of FFA elevation to changes in insulin-mediated glucose uptake was studied. Two groups of lean insulin-sensitive subjects underwent euglycemic-hyperinsulinemic (40 mU x m(-2) x min(-1)) clamp studies with and without superimposed FFA elevation on 2 occasions approximately 4 weeks apart. Groups differed only by duration of FFA elevation, either short (2-4 h, n = 12) or long (8 h, n = 7). On both occasions, rates of whole-body glucose uptake were measured, and changes in leg blood flow (LBF) and femoral vein nitric oxide nitrite plus nitrate (NOx) flux in response to the clamps were determined. Short FFA infusion did not have any significant effect on the parameters of interest. In contrast, long FFA infusion decreased rates of whole-body glucose uptake from 47.7 +/-2.8 to 32.2 +/- 0.6 micromol x kg(-1) x min(-1) (P < 0.01), insulin-mediated increases in LBF from 66 +/- 8 to 37 +/- 7% (P < 0.05), and insulin-induced increases in NOx flux from 25 +/- 9 to 5 +/- 9% (P < 0.05). Importantly, throughout all groups, FFA-induced changes in whole-body glucose uptake correlated significantly with FFA-induced changes in insulin-mediated increases in LBF (r = 0.706, P < 0.001), which indicates coupling of metabolic and vascular effects. In a different protocol, short FFA elevation blunted the LBF response to NG-monomethyl-L-arginine (L-NMMA), which is an inhibitor of NO synthase. LBF in response to L-NMMA decreased by 17.3 +/- 2.4 and 9.0 +/- 1.4% in the groups without and with FFA elevation, respectively (P < 0.05), which indicates that FFA elevation interferes with shear stress-induced NO production. Thus, impairment of shear stress-induced vasodilation and IMV by FFA elevation occurs with different time courses, and impairment of IMV occurs only if glucose metabolism is concomitantly reduced. These findings suggest that NO production in response to the different stimuli may be mediated via different signaling pathways. FFA-induced reduction in NO production may contribute to the higher incidence of hypertension and macrovascular disease in insulin-resistant patients.

Type II diabetes abrogates sex differences in endothelial function in premenopausal women

BACKGROUND

Obesity is a more potent cardiovascular risk factor (CVRF) in men than in women. Because traditional CVRFs cannot fully account for this sex difference, we tested the hypothesis that compared with men, women exhibit more robust endothelial function independent of obesity and that this sex difference is abrogated by diabetes.

METHODS AND RESULTS

We studied leg blood flow (LBF) responses to graded intrafemoral artery infusions of the endothelium-dependent vasodilator methacholine chloride (Mch) and the endothelium-independent vasodilator sodium nitroprusside (SNP) in groups of lean, obese (OB), and type II diabetic (DM) premenopausal women and age- and body mass index-matched men. LBF response to intrafemoral administration of L-NMMA, an inhibitor of nitric oxide synthase, was also assessed in normal men and women. Maximum LBF increments in response to Mch were 347+/-57% versus 231+/-22% in lean women versus men (P<0.05) and 203+/-25% versus 111+/-17% in OB women versus men (P<0.01), respectively. In DM, maximum LBF increments in response to Mch were 104+/-24% and 138+/-33% in women and men, respectively, (P=NS). LBF decrements in response to L-NMMA were 34.9+/-4.1% and 17.1+/-4.2% in women and men, respectively (P<0.01). The response to SNP was not different between sexes and groups.

CONCLUSIONS

Premenopausal nondiabetic women exhibit more robust endothelium-dependent vasodilation owing to higher rates of nitric oxide release than men. Given the protective vascular action of nitric oxide, this difference may partially explain the lower incidence of macrovascular disease in women. In premenopausal women, DM causes impairment of endothelial function beyond that observed with obesity alone and leads to endothelial dysfunction similar to that observed in DM men. These findings may help explain the similar rates of coronary artery disease and mortality in diabetic men and women.

Interaction between insulin sensitivity and muscle perfusion on glucose uptake in human skeletal muscle: evidence for capillary recruitment

Insulin and glucose delivery (muscle perfusion) can modulate insulin-mediated glucose uptake. This study was undertaken to determine 1) to what extent insulin sensitivity modulates the effect of perfusion on glucose uptake and 2) whether this effect is achieved via capillary recruitment. We measured glucose disposal rates (GDRs) and leg muscle glucose uptake (LGU) in subjects exhibiting a wide range of insulin sensitivity, after 4 h of steady-state (SS) euglycemic hyperinsulinemia (>6,000 pmol/l) and subsequently after raising the rate of leg blood flow (LBF) 2-fold with a superimposed intrafemoral artery infusion of methacholine chloride (Mch), an endothelium-dependent vasodilator. LBF was determined by thermodilution: LGU = arteriovenous glucose difference (AVGdelta) x LBF. As a result of the 114+/-12% increase in LBF induced by Mch, the AVGdelta decreased 32+/-4%, and overall rates of LGU increased 40+/-5% (P < 0.05). We found a positive relationship between the Mch-modulated increase in LGU and insulin sensitivity (GDR) (r = 0.60, P < 0.02), suggesting that the most insulin-sensitive subjects had the greatest enhancement of LGU in response to augmentation of muscle perfusion. In separate groups of subjects, we also examined the relationship between muscle perfusion rate and glucose extraction (AVGdelta). Perfusion was either pharmacologically enhanced with Mch or reduced by intra-arterial infusion of the nitric oxide inhibitor N(G)-monomethyl-L-arginine during SS euglycemic hyperinsulinemia. Over the range of LBF, changes in AVGdelta were smaller than expected based on the noncapillary recruitment model of Renkin. Together, the data indicate that 1) muscle perfusion becomes more rate limiting to glucose uptake as insulin sensitivity increases and 2) insulin-mediated increments in muscle perfusion are accompanied by capillary recruitment. Thus, insulin-stimulated glucose uptake displays both permeability- and perfusion-limited glucose exchange properties.

Dual energy X-ray absorptiometry assessment of fat mass distribution and its association with the insulin resistance syndrome

OBJECTIVE

To determine which dual energy X-ray absorptiometry (DXA)-derived indices of fat mass distribution are the most informative to predict the various parameters of the metabolic syndrome.

RESEARCH DESIGN AND METHODS

A total of 87 healthy men, 63 lean (% fat < or =26) and 24 obese (% fat >26), underwent DXA scanning to evaluate body composition with respect to the whole body and the trunk, leg, and abdominal regions from L1 to L4 and from L3 to L4. These regions were correlated with insulin sensitivity determined by the euglycemic-hyperinsulinemic clamp, insulin area under the curve after oral glucose tolerance test (AUC I); triglyceride; total, HDL, and LDL cholesterol; free fatty acids; and blood pressure. The analyses were performed in all subjects, as well as in lean and obese groups separately.

RESULTS

Among the various indices of body fat, DXA-determined adiposity in the abdominal cut at L1-4 level was the most predictive of the metabolic variables, showing significant relationships with glucose infusion rate ([GIR], mg kg(-1) lean body mass x min(-1)), triglyceride, and cholesterol, independent of total-body mass (r = -0.267, P<0.05; r = 0.316, P<0.005; and r = 0.319, P<0.005, respectively). Upon subanalysis, these correlations remained significant in lean men, whereas in obese men, only BMI and the amount of leg fat (negative relationship) showed significant correlations with triglyceride and cholesterol (r = 0.438, P<0.05; r = 0.458, P<0.05; r = -0.439, P<0.05; and r = -0.414, P<0.05, respectively). The results of a multiple regression analysis revealed that 47% of the variance in GIR among all study subjects was predicted by AUC I, fat L1-4, diastolic blood pressure (dBP), HDL, and triglyceride as independent variables. In the lean group, fat L1-4 alone accounted for 33% of the variance of GIR, whereas in obese men, AUC I and dBP explained 68% of the variance in GIR.

CONCLUSIONS

The DXA technique applied for the evaluation of fat distribution can provide useful information regarding various aspects of the insulin resistance syndrome in healthy subjects. DXA can be a valid, accurate, relatively inexpensive, and safer alternative compared with other methods to investigate the role of abdominal body fat distribution on cardiovascular risk factors.

H2O2 causes endothelial barrier dysfunction without disrupting the arginine-nitric oxide pathway

We have previously demonstrated that nitric oxide (.NO) donors attenuate and that inhibition of endogenous nitric oxide synthase (NOS) enhances hydrogen peroxide (H2O2)-mediated porcine pulmonary artery endothelial cell (PAEC) injury. The current study investigates the hypothesis that oxidant-mediated inhibition of NOS contributes to PAEC injury. PAEC barrier function, measured as the transmonolayer clearance of albumin, was significantly impaired by H2O2 (10-100 microM) in the absence of cytotoxicity. Treatment with H2O2 did not alter NOS activity, measured as the conversion of [3H]arginine to [3H]citrulline in PAEC lysates, either immediately after treatment with 0-250 microM H2O2 for 30 min or for up to 120 min after treatment with 100 microM H2O2. H2O2 had little effect on NOS activity in intact PAECs, measured as 1) the formation of [3H]citrulline in [3H]arginine-loaded PAECs, 2) PAEC guanosine 3',5'-cyclic monophosphate content, and 3) PAEC.NO release to the culture media. These results indicate that the arginine-.NO pathway remains intact after exposure to oxidant conditions sufficient to promote functional derangements of vascular endothelial cells.

Endothelial dysfunction is associated with cholesterol levels in the high normal range in humans

BACKGROUND

The purpose of this study was to test the hypothesis that cholesterol levels in the high normal range are associated with impaired endothelium-dependent vasodilation.

METHODS AND RESULTS

We studied leg blood flow (LBF) responses to graded intrafemoral artery infusions of the endothelium-dependent vasodilator methacholine chloride (MCh) or the endothelium-independent vasodilator sodium nitroprusside (SNP) in normal volunteers exhibiting a wide range of total cholesterol levels within the normal range (<75th percentile). LBF increased in a dose-dependent fashion in response to the femoral artery infusions of MCh and SNP (P<.001). LBF responses to MCh were significantly blunted (P<.001) in subjects with high normal cholesterol (195+/-6 mg/dL, n=13) compared with subjects with low normal cholesterol (146+/-5 mg/dL, n=20). Maximal endothelium-dependent vasodilation in the high normal group was decreased by nearly 50% compared with the low normal group (146+/-13% versus 268+/-34%, P<.01). There was a negative correlation between total cholesterol levels and maximal endothelium-dependent vasodilation (total cholesterol, r=-.41, P<.02; LDL cholesterol, r=-.42, P<.02). On the other hand, LBF responses to the endothelium-independent vasodilator SNP did not differ between groups.

CONCLUSIONS

These data suggest that an inverse and continuous relationship exists between the prevailing cholesterol level and endothelium-dependent vasodilation. Moreover, cholesterol levels even in the normal range may be associated with endothelial dysfunction, thus potentially contributing to the increased risk of macrovascular disease conferred by cholesterol elevations.

Elevated circulating free fatty acid levels impair endothelium-dependent vasodilation

We have recently shown that insulin-resistant obese subjects exhibit impaired endothelial function. Here, we test the hypothesis that elevation of circulating FFA to levels seen in insulin-resistant subjects can impair endothelial function. We studied leg blood flow responses to graded intrafemoral artery infusions of the endothelium-dependent vasodilator methacholine chloride (Mch) or the endothelium-independent vasodilator sodium nitroprusside during the infusion of saline and after raising systemic circulating FFA levels exogenously via a low- or high-dose infusion of Intralipid plus heparin or endogenously by an infusion of somatostatin (SRIF) to produce insulinopenia in groups of lean healthy humans. After 2 h of infusion of Intralipid plus heparin, FFA levels increased from 562+/-95 to 1,303+/-188 micromol, and from 350+/-35 to 3,850+/-371 micromol (P < 0.001) vs. saline for both low- and high-dose groups, respectively. Mch-induced vasodilation relative to baseline was reduced by approximately 20% in response to the raised FFA levels in both groups (P < 0.05, saline vs. FFA, ANOVA). In contrast, similar FFA elevation did not change leg blood flow responses to sodium nitroprusside. During the 2-h SRIF infusion, insulin levels fell, and FFA levels rose from 474+/-22 to 1,042+/-116 micromol (P < 0.01); Mch-induced vasodilation was reduced by approximately 20% (P < 0.02, saline vs. SRIF, ANOVA). Replacement of basal insulin levels during SRIF resulted in a fall of FFA levels from 545+/-47 to 228+/-61 micromol, and prevented the impairment of Mch-induced vasodilation seen with SRIF alone. In conclusion, (a) elevated circulating FFA levels cause endothelial dysfunction, and (b) impaired endothelial function in insulin-resistant humans may be secondary to the elevated FFA concentrations observed in these patients.

Effect of perfusion rate on the time course of insulin-mediated skeletal muscle glucose uptake

To better define the time course of skeletal muscle glucose uptake and its modulation by changes in perfusion, we performed systemic euglycemic-hyperinsulinemic clamps (40 mU.m-2.min-1) for a 90-min period in a group of lean, insulin-sensitive subjects (n = 9) on two occasions (approximately 4 wk apart) with insulin-mediated vasodilation intact or inhibited. Insulin-mediated vasodilation was inhibited by an intrafemoral artery infusion of NG-monomethyl-L-arginine (L-NMMA), a specific inhibitor of nitric oxide synthase. During the study, leg blood flow (LBF) and arteriovenous glucose difference (AVG delta) were measured every 10 min; leg glucose uptake (LGU) was calculated as LGU = LBF x AVG delta. The systemic insulin infusion caused a time-dependent increase in LBF from 0.194 +/- 0.024 to 0.349 +/- 0.046 l/min (P < 0.01). The intrafemoral artery infusion of L-NMMA completely inhibited this increase in LBF. AVG delta, LGU, and whole body glucose disposal rates increased in a time-dependent manner in both studies. The maximum AVG delta was lower with insulin-mediated vasodilation intact than when inhibited (25.9 +/- 2.5 vs. 35.0 +/- 1.6 mg/dl, P < 0.001). The time to achieve half-maximal (T1/2) AVG delta was somewhat longer with insulin-mediated vasodilation intact compared with inhibited (35.6 +/- 4.1 vs. 29.7 +/- 1.6 min, P < 0.01). Maximal LGU was 93.9 +/- 26.8 and 57.2 +/- 11.6 mg/min (P < 0.005), and the T1/2 LGU was 50.2 +/- 16.0 and 36.3 +/- 8.8 min (P = 0.1) during intact and inhibited insulin-mediated vasodilation, respectively. Thus insulin-mediated vasodilation has a modest effect in slowing the time course at which insulin stimulates glucose uptake but has a marked effect in augmenting the maximal rate of insulin-stimulated glucose uptake in skeletal muscle. Impaired insulin-mediated vasodilation, as observed in patients with essential hypertension, may explain, at least in part, the insulin resistance observed in these patients.

Obesity/insulin resistance is associated with endothelial dysfunction. Implications for the syndrome of insulin resistance

To test the hypothesis that obesity/insulin resistance impairs both endothelium-dependent vasodilation and insulin-mediated augmentation of endothelium-dependent vasodilation, we studied leg blood flow (LBF) responses to graded intrafemoral artery infusions of methacholine chloride (MCh) or sodium nitroprusside (SNP) during saline infusion and euglycemic hyperinsulinemia in lean insulin-sensitive controls (C), in obese insulin-resistant subjects (OB), and in subjects with non-insulin-dependent diabetes mellitus (NIDDM). MCh induced increments in LBF were approximately 40% and 55% lower in OB and NIDDM, respectively, as compared with C (P < 0.05). Euglycemic hyperinsulinemia augmented the LBF response to MCh by - 50% in C (P < 0.05 vs saline) but not in OB and NIDDM. SNP caused comparable increments in LBF in all groups. Regression analysis revealed a significant inverse correlation between the maximal LBF change in response to MCh and body fat content. Thus, obesity/insulin resistance is associated with (a) blunted endothelium-dependent, but normal endothelium-independent vasodilation and (b) failure of euglycemic hyperinsulinemia to augment endothelium-dependent vasodilation. Therefore, obese/insulin-resistant subjects are characterized by endothelial dysfunction and endothelial resistance to insulin's effect on enhancement of endothelium-dependent vasodilation. This endothelial dysfunction could contribute to the increased risk of atherosclerosis in obese insulin-resistant subjects.

Obesity/insulin resistance is associated with endothelial dysfunction. Implications for the syndrome of insulin resistance

To test the hypothesis that obesity/insulin resistance impairs both endothelium-dependent vasodilation and insulin-mediated augmentation of endothelium-dependent vasodilation, we studied leg blood flow (LBF) responses to graded intrafemoral artery infusions of methacholine chloride (MCh) or sodium nitroprusside (SNP) during saline infusion and euglycemic hyperinsulinemia in lean insulin-sensitive controls (C), in obese insulin-resistant subjects (OB), and in subjects with non-insulin-dependent diabetes mellitus (NIDDM). MCh induced increments in LBF were approximately 40% and 55% lower in OB and NIDDM, respectively, as compared with C (P < 0.05). Euglycemic hyperinsulinemia augmented the LBF response to MCh by - 50% in C (P < 0.05 vs saline) but not in OB and NIDDM. SNP caused comparable increments in LBF in all groups. Regression analysis revealed a significant inverse correlation between the maximal LBF change in response to MCh and body fat content. Thus, obesity/insulin resistance is associated with (a) blunted endothelium-dependent, but normal endothelium-independent vasodilation and (b) failure of euglycemic hyperinsulinemia to augment endothelium-dependent vasodilation. Therefore, obese/insulin-resistant subjects are characterized by endothelial dysfunction and endothelial resistance to insulin's effect on enhancement of endothelium-dependent vasodilation. This endothelial dysfunction could contribute to the increased risk of atherosclerosis in obese insulin-resistant subjects.

Insulin-mediated skeletal muscle vasodilation contributes to both insulin sensitivity and responsiveness in lean humans

Whether insulin-mediated vasodilation is important in determining insulin's overall action to stimulate glucose uptake is unknown. To this end, we measured leg glucose uptake during euglycemic hyperinsulinemic clamps performed at two insulin doses (40 mU/m2 per min, n = 6 and 120 mU/m2 per min, n = 15) alone and during a superimposed intrafemoral artery infusion of GN-monomethyl-L-arginine (L-NMMA) designed to blunt insulin-mediated vasodilation. During the higher dose study, hyperinsulinemia resulted in about a twofold rise in basal leg blood flow from 0.24 +/- 0.02 to 0.45 +/- 0.05 liter/min, P < 0.0001. L-NMMA infusion resulted in a net 21% reduction in leg glucose uptake from 114 +/- 18 mg/min to 85 +/- 13 mg/min, P < 0.001. We also found a significant relationship between the rate of insulin-stimulated whole body glucose uptake and the magnitude of flow dependent glucose uptake (r = 0.57, P = 0.02). Data obtained during the lower dose insulin infusion resulted in similar findings. In conclusion, in healthy lean subjects, insulin-stimulated muscle blood flow contributes to both insulin responsiveness and insulin sensitivity. The most insulin-sensitive subjects appear to be the most reliant on muscle perfusion for insulin action. Insulin-mediated vasodilation is an important physiological determinant of insulin action.

Insulin-mediated skeletal muscle vasodilation is nitric oxide dependent. A novel action of insulin to increase nitric oxide release

The purpose of this study was to examine whether insulin's effect to vasodilate skeletal muscle vasculature is mediated by endothelium-derived nitric oxide (EDNO). N-monomethyl-L-arginine (L-NMMA), a specific inhibitor of NO synthase, was administered directly into the femoral artery of normal subjects at a dose of 16 mg/min and leg blood flow (LBF) was measured during an infusion of saline (NS) or during a euglycemic hyperinsulinemic clamp (HIC) designed to approximately double LBF. In response to the intrafemoral artery infusion of L-NMMA, LBF decreased from 0.296 +/- 0.032 to 0.235 +/- 0.022 liters/min during NS and from 0.479 +/- 0.118 to 0.266 +/- 0.052 liters/min during HIC, P < 0.03. The proportion of NO-dependent LBF during NS and HIC was approximately 20% and approximately 40%, respectively, P < 0.003 (NS vs. HIC). To elucidate whether insulin increases EDNO synthesis/release or EDNO action, vasodilative responses to graded intrafemoral artery infusions of the endothelium-dependent vasodilator methacholine chloride (MCh) or the endothelium-independent vasodilator sodium nitroprusside (SNP) were studied in normal subjects during either NS or HIC. LBF increments in response to intrafemoral artery infusions of MCh but not SNP were augmented during HIC versus NS, P < 0.03. In summary, insulin-mediated vasodilation is EDNO dependent. Insulin vasodilation of skeletal muscle vasculature most likely occurs via increasing EDNO synthesis/release. Thus, insulin appears to be a novel modulator of the EDNO system.

Interactions between insulin and norepinephrine on blood pressure and insulin sensitivity. Studies in lean and obese men

To explore the interactions between insulin action and norepinephrine (NE) on blood pressure and muscle vascular resistance, we studied seven lean (66 +/- 1 kg) sensitive and seven age-matched obese (96 +/- 3 kg) insulin-resistant men after an overnight fast. Both groups were normotensive; however, the obese exhibited higher basal blood pressure, 90.8 +/- 2.2 vs. 83.4 +/- 1.6 mmHg, P < 0.04. Each subject was studied on two separate days during either saline (S) infusion or a euglycemic hyperinsulinemic clamp (I) achieving insulin concentrations of approximately 70 microU/ml. After 180 min of either S or I, NE was infused systemically at rates of approximately 50, 75, and 100 pg/kg per min. Glucose uptake was measured in whole body ([3-3H]glucose) and in leg by the balance technique. The results indicate: (a) the NE/pressor dose-response curve was decreased (shifted to the right) during I in lean but not in obese subjects, (b) I enhanced NE metabolic clearance by 20% in lean but not in obese, (c) NE decreases leg vascular resistance more in lean than in obese, and (d) NE causes a approximately 20% increase in insulin-mediated glucose uptake in both groups. In conclusion, insulin resistance of obesity is associated with an apparent augmented NE pressor sensitivity and decreased NE metabolic clearance. Both of these mechanisms can potentially contribute to the higher incidence of hypertension in obese man. Insulin resistance is likely to be a predisposing but not sufficient factor in the pathogenesis of hypertension. Because the obese group exhibited higher basal blood pressure, it is possible that our results reflect this difference. Further studies will be required to clarify this issue.