Arterial endothelial dysfunction and idiopathic deep venous thrombosis

Recent epidemiological studies have highlighted higher risk of subsequent development of atherosclerotic disease in patients with deep venous thrombosis (DVT). We evaluated the Flow Mediated Dilation (FMD) looking for arterial endothelial dysfunction, predictive for future ischaemic cardiovascular events, in patients with idiopathic DVT. FMD was measured in the brachial artery in 60 subjects with idiopathic DVT (age 60.1±17.4) and in 60 subjects without idiopathic DVT (age 61.2±15.1), with a similar cardiovascular risk factor profile. DVT patients showed lower FMD (6.78%±5.53% vs 10.88±3.31%, p<0.001). Univariate linear models showed that obesity (p=0.010), dyslipidemia (p=0.004), arterial hypertension (p=0.046), use of platelet anti-aggregating agents (p=0.018) and DVT (p<0.001) were associated to lower levels of FMD. In multivariate linear model, only DVT (p<0.001) remained an independent predictor of lower levels of FMD. Furthermore, an 8.5% cut-off value of FMD was chosen in a ROC curve analysis. Values of FMD ≤ 8.5% were more frequent in DVT patients (71.67% vs 41.67%, p<0.001). Univariate logistic regression models showed that dyslipidemia (p=0.008), use of platelet anti-aggregating agents (p=0.004) and DVT (p<0.001) were associated to a higher risk of having FMD ≤ 8.5%. Multivariate logistic regression model showed that DVT was the unique independent predictor for FMD ≤ 8.5% (p<0.001). In conclusion, DVT patients more frequently have impaired FMD, recognized as an indicator of arterial endothelial dysfunction and a marker for increased cardiovascular risk.     

Postprandial endothelial function does not differ in women by race: an insulin resistance paradox?

Insulin resistance is associated with endothelial dysfunction. Because African-American women are more insulin-resistant than white women, it is assumed that African-American women have impaired endothelial function. However, racial differences in postprandial endothelial function have not been examined. In this study, we test the hypothesis that African-American women have impaired postprandial endothelial function compared with white women. Postprandial endothelial function following a breakfast (20% protein, 40% fat, and 40% carbohydrate) was evaluated in 36 (18 African-American women, 18 white women) age- and body mass index (BMI)-matched (age: 37 ± 11 yr; BMI: 30 ± 6 kg/m(2)) women. Endothelial function, defined by percent change in brachial artery flow-mediated dilation (FMD), was measured at 0, 2, 4, and 6 h following a meal. There were no significant differences between the groups in baseline FMD, total body fat, abdominal visceral fat, and fasting levels of glucose, insulin, total cholesterol, low-density lipoprotein cholesterol, or serum estradiol. Although African-American women were less insulin-sensitive [insulin sensitivity index (mean ± SD): 3.6 ± 1.5 vs. 5.2 ± 2.6, P = 0.02], both fasting triglyceride (TG: 56 ± 37 vs. 97 ± 49 mg/dl, P = 0.007) and incremental TG area under the curve (AUC(0-6hr): 279 ± 190 vs. 492 ± 255 mg·dl(-1)·min(-1)·10(-2), P = 0.008) were lower in African-American than white women. Breakfast was associated with a significant increase in FMD in whites and African-Americans, and there was no significant difference in postprandial FMD between the groups (P > 0.1 for group × time interactions). Despite being insulin-resistant, postprandial endothelial function in African-American women was comparable to white women. These results imply that insulin sensitivity may not be an important determinant of racial differences in endothelial function.     

Which endothelium-derived factors are really important in humans?

The endothelium plays a primary role in the local control of vascular function and structure, mainly by the production and release of NO, a potent vasodilator that also inhibits all the mechanisms involved in the pathogenesis of atherosclerosis, thus protecting the vessel wall against the development of atherosclerosis and thrombosis. Cardiovascular risk factors are associated with endothelial dysfunction, which involves enhanced production of oxygen free radicals that reduce NO availability and the release of contracting factors, including prostanoids and endothelin-1. In humans, endothelium-dependent relaxation can be assessed by tests that explore vascular reactivity. Besides the degree of vasodilation, which represents a crude estimate of endothelial function, the utilization of a complex experimental design, requiring the administration of specific agonists and antagonists, allows detailed exploration of the mediators and mechanisms involved in endothelium-dependent vasodilation. At present, the degree of endothelium-dependent vasodilation (evoked by receptor-operated agonists or the application of mechanical forces) is considered an independent predictor of cardiovascular events. In contrast, scant information is available concerning the clinical relevance of different mediators involved in endothelial function. Further studies are needed in the future to assess the specific impact of different endothelial responses on the clinical outcome in patients with cardiovascular risk factors and disease.     

Ultrasound Assessment of Endothelial-Dependent Flow-Mediated Vasodilation of the Brachial Artery in Clinical Research

The vascular endothelium is a monolayer of cells that cover the interior of blood vessels and provide both structural and functional roles. The endothelium acts as a barrier, preventing leukocyte adhesion and aggregation, as well as controlling permeability to plasma components. Functionally, the endothelium affects vessel tone.Endothelial dysfunction is an imbalance between the chemical species which regulate vessel tone, thombroresistance, cellular proliferation and mitosis. It is the first step in atherosclerosis and is associated with coronary artery disease, peripheral artery disease, heart failure, hypertension, and hyperlipidemia.The first demonstration of endothelial dysfunction involved direct infusion of acetylcholine and quantitative coronary angiography. Acetylcholine binds to muscarinic receptors on the endothelial cell surface, leading to an increase of intracellular calcium and increased nitric oxide (NO) production. In subjects with an intact endothelium, vasodilation was observed while subjects with endothelial damage experienced paradoxical vasoconstriction.There exists a non-invasive, in vivo method for measuring endothelial function in peripheral arteries using high-resolution B-mode ultrasound. The endothelial function of peripheral arteries is closely related to coronary artery function. This technique measures the percent diameter change in the brachial artery during a period of reactive hyperemia following limb ischemia.This technique, known as endothelium-dependent, flow-mediated vasodilation (FMD) has value in clinical research settings. However, a number of physiological and technical issues can affect the accuracy of the results and appropriate guidelines for the technique have been published. Despite the guidelines, FMD remains heavily operator dependent and presents a steep learning curve. This article presents a standardized method for measuring FMD in the brachial artery on the upper arm and offers suggestions to reduce intra-operator variability.     

Epicardial fat volume is associated with coronary microvascular response in healthy subjects: a pilot study

Epicardial fat (EF) is an active ectopic fat depot, which has been associated with coronary atherosclerosis, and which could early influence endothelial function. We thus investigated the relationship between EF and endothelium-dependent vasoreactivity of the coronary microcirculation, in highly selected healthy volunteers. Myocardial blood flow (MBF) was determined by measuring coronary sinus flow with velocity-encoded cine magnetic resonance imaging (MRI) at 3T. We measured MBF at baseline and in response to sympathetic stimulation by cold pressor testing (CPT) in 30 healthy volunteers with normal left ventricular (LV) function (age 22 ± 4 years, BMI = 21.3 ± 2.8 kg/m(2)). EF volume was volumetrically assessed by manual delineation on short-axis views. CPT was applied by immersing one foot in ice water for 4 min. Mean EF volume was 56 ± 26 ml and mean LV mass 100 ± 28 g. CPT significantly increased heart rate (HR) by 32 ± 19%, systolic blood pressure by 14 ± 10%, and rate-pressure product by 45 ± 25%, P < 0.0001. The increase in HR, reflecting sympathetic stimulation, was not influenced by sex, age or EF volume. CPT induced a decrease in coronary vascular resistance (135 ± 72 vs. 100 ± 42 mm Hg.ml(-1).min.g, P = 0.0006), and a significant increase in MBF (0.81 ± 0.37 vs. 1.24 ± 0.56 ml.min(-1).g(-1), P < 0.0001). Interestingly, we found a significant negative correlation between EF volume and ΔMBF (r= - 0.40, P = 0.03), which remained significant after adjusting for ΔHR. ΔMBF was also associated with adiponectin (r = 0.41, P = 0.046), but not with waist circumference, BMI, C-reactive protein, lipid or glycemic parameters. In multivariate analysis, adiponectin and EF volume remained both independently associated with ΔMBF. A high EF amount is associated with a lower coronary microvascular response, suggesting that EF could early influence endothelial function.     

Increased inactivation of nitric oxide is involved in coronary endothelial dysfunction in heart failure

Recent evidence suggests the possibility that enhanced inactivation of endothelium-derived nitric oxide (NO) by oxygen free radical (OFR) may cause endothelial dysfunction in heart failure (HF). To test this hypothesis, we examined the effect of antioxidant therapy on endothelium-dependent vasodilation of the coronary circulation in a canine model of tachycardia-induced HF. Endothelium-dependent vasodilation was less than that in controls, and OFR formation in coronary arterial and myocardial tissues was greater in HF dogs than those in controls. The immunohistochemical staining of 4-hydroxy-2-nonenal, OFR-induced lipid peroxides was detected in coronary microvessels of HF dogs. Intracoronary infusion of the cell-permeable OFR scavenger Tiron inhibited OFR formation and improved endothelium-dependent vasodilation in HF dogs but not in controls. The NO synthesis inhibitor N(G)-monomethyl-L-arginine (L-NMMA) diminished the beneficial effect of Tiron in HF dogs. Endothelium-independent vasodilation was similar between control and HF dogs, and no change in its response was noted by Tiron or Tiron plus L-NMMA in either group. In summary, antioxidant treatment with Tiron improved coronary vascular endothelium-dependent vasodilation by increasing NO activity in tachycardia-induced HF. Thus coronary endothelial dysfunction in HF may be, at least in part, due to increased inactivation of NO by OFR.     

In vivo measurement of flow-mediated vasodilation in living rats using high-resolution ultrasound

In humans, endothelial vasodilator function serves as a surrogate marker for cardiovascular health and is measured as changes in conduit artery diameter after temporary ischemia [flow-mediated dilation (FMD)]. Here we present an FMD-related approach to study femoral artery (FA) vasodilation in anesthetized rats. Diameter and Doppler flow were monitored in the FA. Using high-resolution ultrasound (35 MHz) and automated analysis software, we detected dose-dependent vasodilation using established endothelium-independent [intravenous nitroglycerin EC(50) = 3.3 x 10(-6) mol/l, peak 21Delta% (SD 4)] and endothelium-dependent [intra-arterial acetylcholine EC(50) = 1.3 x 10(-6) mol/l, peak 27Delta% (SD 4)] pharmacological vasodilators. Wall shear stress induced by intra-aortic injection of adenosine and infusion of saline at increasing rates (1.5-4.5 ml/min) led to vasodilation at 1 to 2 min. Transient hindlimb ischemia by common iliac occlusion (5 min) led to reactive hyperemia with flow velocity and wall shear stress increase and was followed by FA dilation [16Delta% (SD 2)], the latter of which was completely abolished by nitric oxide synthase (NOS) inhibition with N(G)-monomethyl-L-arginine [1Delta% (SD 2)]. FMD was significantly reduced in adult 20-24-wk-old animals compared with 9- to 10-wk-old animals, consistent with age-dependent endothelial dysfunction [16Delta% (SD 3) vs. 10Delta% (SD 3), P < 0.05]. Whereas FMD was completely NOS dependent in 9- to 10-wk-old animals, NOS-dependent mechanisms accounted for only half of the FMD in 20-24-wk-old animals, with the remainder being blocked by charybdotoxin and apamin, suggesting a contribution of endothelium-derived hyperpolarizing factor. To our knowledge, this is the first integrative physiological model to reproducibly study FMD of conduit arteries in living rats.     

Coronary endothelial dysfunction is not rapidly reversible with ascorbic acid

In humans with cardiovascular risk factors, increased vascular production of superoxide anion may contribute to endothelial dysfunction by its reacting with nitric oxide and reducing its biological activity. High concentrations of ascorbic acid scavenge superoxide anion and restore normal endothelium-dependent vasodilation in humans with cardiovascular risk factors. To investigate the contribution of increased superoxide anion to endothelial dysfunction in atherosclerotic coronary arteries, we examined the effect of sequential infusions of ascorbic acid (final concentration 0.1, 1.0, and 10 mmol/L) or placebo on coronary endothelial function in 26 subjects referred for cardiac catheterization to evaluate coronary artery disease. Coronary vasomotor function was evaluated using intracoronary agonist infusion, quantitative angiography, and intracoronary Doppler measurements. At baseline, endothelium-dependent vasodilation of epicardial arteries and coronary microvessels was impaired to an equivalent extent in the ascorbic acid and placebo groups. Sequential ascorbic acid infusions had no effect on the acetylcholine-induced change in coronary artery diameter (-11+/-8, -12+/-10, and -9+/-9%) compared with the effect of placebo (-14+/-13, -16+/-10, and -13+/-9%) infusions (p=0.98). Similarly, the changes in coronary blood flow during acetylcholine infusions were equivalent during ascorbic acid (51+/-44, 67+/-66, and 62+/-52%) and placebo (61+/-104, 55+/-93, and 50+/-69%) infusions (p=0.63). Ascorbic acid also had no effect on the dilator response to intracoronary nitroglycerin (p=0.19). These data argue against an important role for superoxide-mediated "inactivation" of nitric oxide or another rapidly reversible form of oxidative stress as a mechanism of coronary endothelial dysfunction in patients with coronary atherosclerosis.     

Impaired flow-mediated dilation with age is not explained by L-arginine bioavailability or endothelial asymmetric dimethylarginine protein expression.

Aging is associated with a decline in vascular endothelial function, manifesting in part as impaired flow-mediated arterial dilation (FMD), but the underlying mechanisms are uncertain. Impaired FMD may be mediated in part by a decrease in synthesis of nitric oxide by endothelial nitric oxide synthase, and in clinical populations this has been attributed to competitive inhibition of l-arginine binding sites by asymmetric dimethylarginine (ADMA). If this mechanism is involved in the age-associated decline in FMD, increasing l-arginine concentration may swing the competitive balance in favor of l-arginine binding, restoring nitric oxide synthesis, and enhancing FMD in older humans. To test this hypothesis, we measured FMD (brachial ultrasound) in 10 younger (21 +/- 1 yr) and 12 older healthy men and women (60 +/- 2 yr) following infusion of vehicle or vehicle + l-arginine. Baseline FMD in the older subjects was only approximately 60% of that in the younger subjects (P = 0.002). l-Arginine did not significantly increase FMD in either group despite 23-fold (older) and 19-fold (younger) increases in plasma l-arginine concentrations (P < 0.0001 vs. control). Protein expression (immunofluorescence) in vascular endothelial cells showed that ADMA and the enzyme isoform that controls its degradation, dimethylarginine dimethylaminohydrolase II, were not different in the younger and older subjects. Endothelium-independent vasodilation (sublingual nitroglycerine) was not different between age groups or conditions. We conclude that acutely increasing plasma concentrations of l-arginine do not significantly improve brachial artery FMD in healthy older subjects and thus does not restore the age-associated loss of FMD. Together with the finding that endothelial cell ADMA protein expression was not increased in older adults, these findings suggest that competitive inhibition of l-arginine binding sites on endothelial nitric oxide synthase by ADMA is not an important mechanism contributing to impaired conduit artery endothelium-dependent dilation with aging in healthy humans.     

Skin Autofluorescence Is Associated with Endothelial Dysfunction in Uremic Subjects on Hemodialysis

Background

Elevated levels of advanced glycation end products (AGEs) within tissues may contribute to endothelial dysfunction, an early indicator of atherosclerosis. We aimed to investigate whether levels of skin AGEs could be a useful marker to predict endothelial dysfunction in uremic subjects on hemodialysis.

Methods and Results

One hundred and nineteen uremic patients on hemodialysis and 57 control subjects with moderate-to-high cardiovascular risk factors and without chronic kidney disease (CKD) were enrolled. We used ultrasound to measure flow-mediated vasodilation (FMD). An AGE reader measured skin autoflurorescence (AF). We then compared differences in FMD and skin AF values between the two groups. The uremic subjects had significantly higher levels of skin AF (3.47±0.76 AU vs. 2.21±0.45 arbitrary units; P<0.01) and significantly lower levels of FMD (4.79%±1.88% vs. 7.19%±2.17%; P<0.01) than the non-CKD subjects. After adjusting for all potential covariates, we found that skin AF level independently predicted FMD in both the hemodialysis and the non-CKD groups. In the hemodialysis group, skin AF ≥ 3.05 arbitrary units predicted abnormal FMD at a sensitivity of 87.9% and a specificity of 78.6% (P<0.01).

Conclusions

Skin AF could be a useful marker to predict endothelial dysfunction in uremic subjects on hemodialysis.     

Acute vascular responses to isometric handgrip exercise and effects of training in persons medicated for hypertension

Previous work from our laboratory demonstrated that isometric handgrip (IHG) training improved local, endothelium-dependent vasodilation in medicated hypertensives [McGowan CL (PhD Thesis), 2006; McGowan et al. Physiologist 47: 285, 2004]. We investigated whether changes in the capacity of smooth muscle to dilate (regardless of endothelial factors) influenced this training-induced change, and we examined the acute vascular responses to a single bout of IHG. Seventeen subjects performed four 2-min unilateral IHG contractions at 30% of maximal voluntary effort, three times a week for 8 wk. Pre- and posttraining, brachial artery flow-mediated dilation (FMD, an index of endothelium-dependent vasodilation) and nitroglycerin-mediated maximal vasodilation (an index of endothelium-independent vasodilation) were measured in the exercised arm by using ultrasound before and immediately after acute IHG exercise. IHG training resulted in improved resting brachial FMD (P < 0.01) and no change in nitroglycerin-mediated maximal vasodilation. Pre- and posttraining, brachial artery FMD decreased following an acute bout of IHG exercise (normalized to peak shear rate, pre-, before IHG exercise: 0.01 +/- 0.002, after IHG exercise: 0.008 +/- 0.002%/s(-1); post-, before IHG exercise: 0.020 +/- 0.003, after IHG exercise: 0.010 +/- 0.003%/s(-1); P < 0.01). Posttraining, resting brachial artery FMD improved yet nitroglycerin-mediated maximal vasodilation was unchanged in persons medicated for hypertension. This suggests that the training-induced improvements in the resting brachial artery FMD were not due to underlying changes in the forearm vasculature. Acute IHG exercise attenuated brachial artery FMD, and although this impairment may be interpreted as hazardous to medicated hypertensives with already dysfunctional endothelium, the effects appear transient as repeated exposure to the IHG stimulus improved resting endothelium-dependent vasodilation.     

Influence of Visceral Obesity and Liver Fat on Vascular Structure and Function in Obese Subjects

Endothelial dysfunction and increased intima–media thickness (IMT) have been found in obese patients. Both regional fat distribution and liver steatosis may influence these markers of subclinical atherosclerosis. We sought to determine the interrelationships of endothelial function, carotid IMT, visceral and subcutaneous adipose tissue accumulation, and liver steatosis in severely obese subjects. In 64 severely obese patients (BMI 42.3 ± 4.3 kg/m²), we determined (i) endothelial function as flow‐mediated dilation (FMD) of the brachial artery, (ii) carotid IMT, (iii) visceral fat diameter, and (iv) degree of liver steatosis using ultrasound. FMD was associated inversely with visceral fat diameter and degree of steatosis (r = ?0.577, P < 0.0001 and r = ?0.523, P < 0.0001, respectively). Carotid IMT correlated with visceral fat mass (r = 0.343, P = 0.007) but not with liver steatosis. After adjustment for conventional cardiovascular risk factors, FMD was predicted independently by the visceral fat diameter, age, and sex (r² = 0.48, P < 0.0001), but not by the degree of liver steatosis or plasma adiponectin levels. In contrast, age and sex were the only predictors of IMT (r² = 0.33, P < 0.001). In obese patients, visceral fat diameter is a major determinant of endothelial dysfunction, independent of traditional risk factors or the degree of liver steatosis and plasma adiponectin. Measurement of visceral fat diameter by ultrasound is a novel and simple method to identify subjects with an increased risk for atherosclerosis within an obese population.     

The lp13.3 genomic region -rs599839- is associated with endothelial dysfunction in patients with rheumatoid arthritis

Introduction

Rheumatoid arthritis (RA) is an inflammatory disease associated with accelerated atherosclerosis and high risk of cardiovascular (CV) disease. Since genome-wide association studies demonstrated association between rs599839 polymorphism and coronary artery disease, in the present study we assessed the potential association of this polymorphism with endothelial dysfunction, an early step in atherogenesis.

Methods

A total of 128 RA patients without history of CV events were genotyped for rs599839 A/G polymorphism. The presence of endothelial dysfunction was assessed by brachial ultrasonography (brachial flow-mediated endothelium-dependent (FMD)).

Results

Patients carrying the allele G exhibited more severe endothelial dysfunction (FMD%: 4.61 ± 3.94%) than those carrying the wild allele A (FMD%: 6.01 ± 5.15%) (P = 0.08). Adjustment for gender, age at the time of study, follow-up time and classic CV risk factors disclosed a significant association between the rs599839 polymorphism and FMD (G vs. A: P = 0.0062).

Conclusions

Our results confirm an association of the rs599839 polymorphism with endothelial dysfunction in RA.     

Loss of the preconditioning effect of rosuvastatin during sustained therapy: a human in vivo study

Studies have demonstrated that the acute administration of 3-hydroxy-3 methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors has protective effects in the setting of ischemia-reperfusion (IR). Previously, we demonstrated that a single dose of rosuvastatin prevented IR-induced endothelial dysfunction in humans through a cyclooxygenase-2-dependent mechanism. Whether the chronic administration of HMG-CoA reductase inhibitors provides similar protection remains controversial and is unknown in humans. Eighteen male volunteers were randomized to receive a single dose of rosuvastatin (20 mg) or placebo. Twenty-four hours later, endothelium-dependent, radial artery flow-mediated dilation (FMD) was measured before and after IR (15 min of upper arm ischemia followed by 15 min of reperfusion). In a separate protocol, 30 healthy volunteers were randomized in a double-blind fashion to receive oral rosuvastatin (20 mg/day) and placebo, rosuvastatin, and celecoxib (100 mg bid) or placebo alone, all for 21 days. Twenty-four hours after the final administration of study medication, FMD was measured before and after IR. Pre-IR FMD was similar between groups in both protocols. In the acute administration protocol, rosuvastatin significantly prevented the blunting of FMD associated with IR (FMD pre-IR: 8.4 ± 1.3%; post-IR: 6.2 ± 1.3%; P = 0.01 ANOVA, treatment group interaction). In the daily administration protocol, IR significantly blunted FMD in the placebo group (FMD pre-IR: 7.5 ± 0.9%; post-IR: 3.3 ± 0.7%; P < 0.001). Chronic treatment with rosuvastatin did not modify this ischemic injury (FMD pre-IR: 6.9 ± 0.4%; post-IR: 1.6 ± 1.0%; P < 0.001; P = NS ANOVA, treatment group interaction). Similarly, FMD responses post-IR in volunteers receiving rosuvastatin and celecoxib did not significantly differ from placebo (FMD pre-IR: 8.3 ± 0.9%; post-IR: 2.1 ± 0.8%; P < 0.001; P = NS ANOVA, treatment group interaction). In contrast to acute administration, chronic rosuvastatin does not prevent the development of IR-induced endothelial dysfunction in normal humans.     

Dose-dependent increases in flow-mediated dilation following acute cocoa ingestion in healthy older adults

An inverse relation exists between intake of flavonoid-rich foods, such as cocoa, and cardiovascular-related mortality. Favorable effects of flavonoids on the endothelium may underlie these associations. We performed a randomized, double-blind, placebo-controlled study to test the hypothesis that acute cocoa ingestion dose dependently increases endothelium-dependent vasodilation, as measured by an increase in brachial artery flow-mediated dilation (FMD), in healthy older adults. Measurements were obtained before (preingestion) and after (1- and 2-h postingestion) ingestion of 0 (placebo), 2, 5, 13, and 26 g of cocoa in 23 adults (63 ± 2 yr old, mean ± SE). Changes in brachial artery FMD 1- and 2-h postingestion compared with preingestion were used to determine the effects of cocoa. FMD was unchanged 1 (Δ-0.3 ± 0.2%)- and 2-h (Δ0.1 ± 0.1%) after placebo (0 g cocoa). In contrast, FMD increased both 1-h postingestion (2 g cocoa Δ0.0 ± 0.2%, 5 g cocoa Δ0.8 ± 0.3%, 13 g cocoa Δ1.0 ± 0.3%, and 26 g cocoa Δ1.6 ± 0.3%: P < 0.05 compared with placebo for 5, 13, and 26 g cocoa) and 2-h postingestion (2 g cocoa Δ0.5 ± 0.3%, 5 g cocoa Δ1.0 ± 0.3%, 13 g cocoa Δ1.4 ± 0.2%, and 26 g cocoa Δ2.5 ± 0.4%: P < 0.05 compared with placebo for 5, 13, and 26 g cocoa) on the other study days. A serum marker of cocoa ingestion (total epicatechin) correlated with increased FMD 1- and 2-h postingestion (r = 0.44-0.48; both P < 0.05). Collectively, these results indicate that acute cocoa ingestion dose dependently increases brachial artery FMD in healthy older humans. These responses may help to explain associations between flavonoid intake and cardiovascular-related mortality in humans.     

Sinusoidal endothelial dysfunction precedes inflammation and fibrosis in a model of NAFLD

Non-alcoholic fatty liver disease (NAFLD) is the hepatic manifestation of the metabolic syndrome. Most morbidity associated with the metabolic syndrome is related to vascular complications, in which endothelial dysfunction is a major pathogenic factor. However, whether NAFLD is associated with endothelial dysfunction within the hepatic vasculature is unknown. The aims of this study were to explore, in a model of diet-induced overweight that expresses most features of the metabolic syndrome, whether early NAFLD is associated with liver endothelial dysfunction. Wistar Kyoto rats were fed a cafeteria diet (CafD; 65% of fat, mostly saturated) or a control diet (CD) for 1 month. CafD rats developed features of the metabolic syndrome (overweight, arterial hypertension, hypertryglyceridemia, hyperglucemia and insulin resistance) and liver steatosis without inflammation or fibrosis. CafD rats had a significantly higher in vivo hepatic vascular resistance than CD. In liver perfusion livers from CafD rats had an increased portal perfusion pressure and decreased endothelium-dependent vasodilation. This was associated with a decreased Akt-dependent eNOS phosphorylation and NOS activity. In summary, we demonstrate in a rat model of the metabolic syndrome that shows features of NAFLD, that liver endothelial dysfunction occurs before the development of fibrosis or inflammation.     

Endothelial ischemia-reperfusion injury in humans: association with age and habitual exercise

Advancing age is a major risk factor for coronary artery disease. Endothelial dysfunction accompanied by increased oxidative stress and inflammation with aging may predispose older arteries to greater ischemia-reperfusion (I/R) injury. Because coronary artery ischemia cannot be induced safely, the effects of age and habitual endurance exercise on endothelial I/R injury have not been determined in humans. Using the brachial artery as a surrogate model of the coronary arteries, endothelial function, assessed by brachial artery flow-mediated dilation (FMD), was measured before and after 20 min of continuous forearm occlusion in young sedentary (n = 10, 24 ± 2 yr) and middle-aged (n = 9, 48 ± 2 yr) sedentary adults to gain insight into the effects of primary aging on endothelial I/R injury. Young (n = 9, 25 ± 1 yr) and middle-aged endurance-trained (n = 9, 50 ± 2 yr) adults were also studied to determine whether habitual exercise provides protection from I/R injury. Fifteen minutes after ischemic injury, FMD decreased significantly by 37% in young sedentary, 35% in young endurance-trained, 68% in middle-aged sedentary, and 50% in middle-aged endurance-trained subjects. FMD returned to baseline levels within 30 min in young sedentary and endurance-trained subjects but remained depressed in middle-aged sedentary and endurance-trained subjects. Circulating markers of antioxidant capacity and inflammation were not related to FMD. In conclusion, advancing age is associated with a greater magnitude and delayed recovery from endothelial I/R injury in humans. Habitual endurance exercise may provide partial protection to the endothelium against this form of I/R injury with advancing age.     

Differential Effect of Amylin on Endothelial-Dependent Vasodilation in Mesenteric Arteries from Control and Insulin Resistant Rats

Insulin resistance (IR) is frequently associated with endothelial dysfunction and has been proposed to play a major role in cardiovascular disease (CVD). On the other hand, amylin has long been related to IR. However the role of amylin in the vascular dysfunction associated to IR is not well addressed. Therefore, the aim of the study was to assess the effect of acute treatment with amylin on endothelium-dependent vasodilation of isolated mesenteric arteries from control (CR) and insulin resistant (IRR) rats and to evaluate the possible mechanisms involved. Five week-old male Wistar rats received 20% D-fructose dissolved in drinking water for 8 weeks and were compared with age-matched CR. Plasmatic levels of glucose, insulin and amylin were measured. Mesenteric microvessels were dissected and mounted in wire myographs to evaluate endothelium-dependent vasodilation to acetylcholine. IRR displayed a significant increase in plasmatic levels of glucose, insulin and amylin and reduced endothelium-dependent relaxation when compared to CR. Acute treatment of mesenteric arteries with r-amylin (40 pM) deteriorated endothelium-dependent responses in CR. Amylin-induced reduction of endothelial responses was unaffected by the H₂O₂ scavenger, catalase, but was prevented by the extracellular superoxide scavenger, superoxide dismutase (SOD) or the NADPH oxidase inhibitor (VAS2870). By opposite, amylin failed to further inhibit the impaired relaxation in mesenteric arteries of IRR. SOD, or VAS2870, but not catalase, ameliorated the impairment of endothelium-dependent relaxation in IRR. At concentrations present in insulin resistance conditions, amylin impairs endothelium-dependent vasodilation in mircrovessels from rats with preserved vascular function and low levels of endogenous amylin. In IRR with established endothelial dysfunction and elevated levels of amylin, additional exposure to this peptide has no effect on endothelial vasodilation. Increased superoxide generation through NADPH oxidase activity may be a common link involved in the endothelial dysfunction associated to insulin resistance and to amylin exposure in CR.     

Resistance and aerobic exercise protects against acute endothelial impairment induced by a single exposure to hypertension during exertion

Resistance and aerobic exercise is recommended for cardiovascular health and disease prevention. However, the accompanying increase in arterial pressure during resistance exercise may be detrimental to vascular health. This study tests the vascular benefits of aerobic compared with resistance exercise on preventing impaired vascular function induced by a single weight lifting session that is associated with acute hypertension. Healthy, lean sedentary (SED) subjects, weight lifters, runners (>15 miles/wk), and cross trainers (chronic aerobic and resistance exercisers), underwent a single progressive leg press weight lifting session with blood pressure measurements. Brachial artery flow-mediated vasodilation (FMD; an index of arterial endothelial function) was determined using ultrasonography immediately before and after weight lifting. Sublingual nitroglycerin (0.4 mg) was used to determine endothelium-independent dilation after weight lifting. All subjects were normotensive with similar blood pressure responses during exercise. Baseline FMD was lower in runners (5.4 ± 0.5%; n = 13) and cross trainers (4.44 ± 0.3%; n = 13) vs. SED (8.5 ± 0.8%; n = 13; P = 0.037). Brachial FMD improved in conditioned weight lifters (to 8.8 ± 0.9%; P = 0.007) and runners (to 7.6 ± 0.6%; P < 0.001) but not cross trainers (to 5.3 ± 0.6%; P = NS) after acute hypertension. FMD was decreased in SED (to 5.7 ± 0.4%; P = 0.019). Dilation to nitroglycerin was similar among groups. These data suggest that endothelial responses are maintained after exposure to a single bout of weight lifting in resistance and aerobic athletes. Resistance and aerobic exercise may confer similar protection against acute vascular insults such as exertional hypertension.     

Sex differences in salt sensitivity to nitric oxide dependent vasodilation in healthy young adults

Dietary sodium and blood pressure regulation differs between normotensive men and women, an effect which may involve endothelial production of nitric oxide (NO). Therefore, we tested the hypothesis that differences in the NO component of endothelium-dependent vasodilation between low and high dietary sodium intake depend on sex. For 5 days prior to study, healthy adults consumed a controlled low-sodium diet (10 mmol/day, n = 30, mean age ± SE: 30 ± 1 yr, 16 men) or high-sodium diet (400 mmol/day, n = 36, age 23 ± 1 yr, 13 men). Forearm blood flow (FBF, plethysmography) responses to brachial artery administration of acetylcholine (ACh, 4 μg·100 ml tissue(-1)·min(-1)) were measured before and after endothelial NO synthase inhibition with N(G)-monomethyl-l-arginine (l-NMMA, 50 mg bolus + 1 mg/min infusion). The NO component of endothelium-dependent dilation was calculated as the response to ACh before and after l-NMMA accounting for changes in baseline FBF: [(FBF ACh - FBF baseline) - (FBF ACh(L-NMMA) - FBF baseline(L-NMMA))]. This value was 5.7 ± 1.3 and 2.5 ± 0.8 ml·100 ml forearm tissue(-1)·min(-1) for the low- and high-sodium diets, respectively (main effect of sodium, P = 0.019). The sodium effect was larger for the men, with values of 7.9 ± 2.0 and 2.2 ± 1.4 for men vs. 3.1 ± 1.3 and 2.7 ± 1.0 ml·100 ml forearm tissue(-1)·min(-1) for the women (P = 0.034, sex-by-sodium interaction). We conclude that the NO component of endothelium-dependent vasodilation is altered by dietary sodium intake based on sex, suggesting that endothelial NO production is sensitive to dietary sodium in healthy young men but not women.