New Methods to Evaluate Endothelial Function: Method for Assessing Endothelial Function in Humans Using a Strain-Gauge Plethysmography: Nitric Oxide-Dependent and -Independent Vasodilation

Endothelial Function in Pulmonary Arterial Hypertension: From Bench to Bedside

Pulmonary arterial hypertension is a complex pathology whose etiology is still not completely well clarified. The pathogenesis of pulmonary arterial hypertension involves different molecular mechanisms, with endothelial dysfunction playing a central role in disease progression. Both individual genetic predispositions and environmental factors seem to contribute to its onset. To further understand the complex relationship between endothelial and pulmonary hypertension and try to contribute to the development of future therapies, we report a comprehensive and updated review on endothelial function in pulmonary arterial hypertension.

Fabricating a multi-component microfluidic system for exercise-induced endothelial cell mechanobiology guided by hemodynamic similarity

Generating precise in vivo arterial endothelial hemodynamic microenvironments using microfluidics is essential for exploring endothelial mechanobiology. However, a hemodynamic principle guiding the fabrication of microfluidic systems is still lacking. We propose a hemodynamic similarity principle for quickly obtaining the input impedance of the microfluidic system in vitro derived from that of the arterial system in vivo to precisely generate the desired endothelial hemodynamic microenvironments. First, based on the equivalent of blood pressure (BP) and wall shear stress (WSS) waveforms, we establish a hemodynamic similarity principle to efficiently map the input impedance in vivo to that in vitro, after which the multi-component microfluidic system is designed and fabricated using a lumped parameter hemodynamic model. Second, numerical simulation and experimental studies are carried out to validate the performance of the designed microfluidic system. Finally, the intracellular Ca²⁺ responses after exposure to different intensities of exercise-induced BP and WSS waveforms are measured to improve the reliability of EC mechanobiological studies using the designed microfluidic system. Overall, the proposed hemodynamic similarity principle can guide the fabrication of a multi-component microfluidic system for endothelial cell mechanobiology.

Dual impedance cardiography: An inexpensive and reliable method to assess arterial stiffness

Pulse wave velocity (PWV) is a common measure of arterial stiffness. Non-invasive methods to measure PWV are widely used in biomedical studies of aging and cardiovascular disease, but they are rarely used in psychophysiology. Barriers to wider use include the prohibitive costs of specialized equipment and need for trained technicians (e.g., ultrasonographers). Here, we describe an impedance cardiography method to measure PWV. By this method, impedance signals are dually collected from the thorax and calf. Combined with ensemble averaging of vascular signals, this dual impedance cardiography (d-ICG) method allows for the measurement of aortic flow onset and the arrival time of peripheral pulse waveforms to compute PWV. In a community sample of adults (aged 19-78 years), PWV measured with d-ICG exhibited a strong positive correlation with age. Moreover, age-specific mean PWV values were within the normative reference intervals established by large scale studies using other techniques. PWV derived from d-ICG exhibited high test-retest reliability across several days, as well as excellent inter-rater reliability. Last, PWV exhibited expected associations with known cardiovascular disease risk factors and indicators of autonomic cardiovascular control. d-ICG is an inexpensive and reliable method to assess arterial stiffness.

Overview of the Assessment of Endothelial Function in Humans

The endothelium is recognized to play an important role in various physiological functions including vascular tone, permeability, anticoagulation, and angiogenesis. Endothelial dysfunction is increasingly recognized to contribute to pathophysiology of many disease states, and depending on the disease stimuli, mechanisms underlying the endothelial dysfunction may be markedly different. As such, numerous techniques to measure different aspects of endothelial dysfunction have been developed and refined as available technology improves. Current available reviews on quantifying endothelial dysfunction generally concentrate on a single aspect of endothelial function, although diseases may affect more than one aspect of endothelial function. Here, we aim to provide an overview on the techniques available for the assessment of the different aspects of endothelial function in humans, human tissues or cells, namely vascular tone modulation, permeability, anticoagulation and fibrinolysis, and the use of endothelial biomarkers as predictors of outcomes.

ROS and NO Dynamics in Endothelial Cells Exposed to Exercise-Induced Wall Shear Stress

Introduction

Intracellular reactive oxygen species (ROS) and nitric oxide (NO) levels are associated with vascular homeostasis and diseases. Exercise can modulate ROS and NO production through increasing frequency and magnitude of wall shear stress (WSS). However, the details of ROS and NO production in endothelial cells and their interplay under WSS induced by exercise at different intensities remain unclear.

Methods

In this study, we developed an in vitro multicomponent nonrectangular flow chamber system to simulate pulsatile WSS waveforms induced by moderate and high intensity exercise. Furthermore, the dynamic responses of ROS and NO in endothelial cells and the relationship between ROS and NO were investigated under the WSS induced by different intensity exercise.

Results

After exposing to WSS induced by moderate intensity exercise, endothelial cells produced more NO than those under high intensity exercise-induced WSS. In this process, ROS was found to play a dual role in the generation of intracellular NO. Under WSS induced by moderate intensity exercise, modest elevated ROS promoted NO production, whereas excessive ROS in endothelial cells exposed to WSS induced by high intensity exercise attenuated NO bioavailability. Interestingly, antioxidant N-acetylcysteine (NAC) could increase NO production under WSS induced by high intensity exercise.

Conclusions

Our results provide some cues for selecting appropriate exercise intensities and elevating benefits of exercise on endothelial function. Additionally, owing to the consistency of our results and some in vivo phenomena, this flow chamber system may serve as an in vitro exercise model of arterial vessel for future studies.

Increased Pre- and Post-Meal Free Fatty Acid Levels in Black, Obese Adolescents

BACKGROUND

Black adolescents are at increased risk of cardiometabolic disease but have lower fasting triglyceride, which is usually associated with decreased risk. No one has studied racial differences in triglycerides or free fatty acids (FFAs) after a high-fat meal.

METHODS

Oral glucose tolerance testing was used to assess insulin secretion, sensitivity, and disposition index (DI). Endothelial function, triglycerides, FFA, c-reactive protein, interleukin 6 (IL6), and adiponectin were measured both pre- and 3 hr postprandially (McDonald's Big Breakfast(®) and 12 ounce Sprite(®)) in obese adolescents (10-13 years, 9 black and 7 white). Endothelial function was assessed using reactive hyperemic changes in forearm vascular resistance (FVR).

RESULTS

Oral glucose tolerance test (OGTT) showed no difference in insulin sensitivity, but blacks tended to have (P = 0.08) higher insulin secretion and had increased DI (P = 0.003). After a high-fat meal, triglycerides increased in both groups (P < 0.001), tended to be lower in blacks compared with whites preprandially (64 ± 33 mg/dL vs 110 ± 80, P = 0.064), and was lower postprandially (112 ± 63 vs 188 ± 112, P = 0.039). Pre- and postprandial FFA (Black: 0.58 ± 0.15 and 0.39 ± 0.18 vs. white: 0.44 ± 0.14 and 0.26 ± 0.06, P = 0.020) and adiponectin (P = 0.002) were increased in blacks. FFA decreased in both groups postprandially (P = 0.002). IL6 increased after the meal (P = 0.022). Endothelial function decreased postprandially (P < 0.02), but this was due to a decrease in preocclusion FVR.

CONCLUSIONS

These results indicate that differences in fat metabolism are present in both black and white obese adolescents. How these differences explain higher rates of cardiometabolic disease in blacks is unclear.

Multi-scale Modeling of the Cardiovascular System: Disease Development, Progression, and Clinical Intervention

Cardiovascular diseases (CVDs) are the leading cause of death in the western world. With the current development of clinical diagnostics to more accurately measure the extent and specifics of CVDs, a laudable goal is a better understanding of the structure-function relation in the cardiovascular system. Much of this fundamental understanding comes from the development and study of models that integrate biology, medicine, imaging, and biomechanics. Information from these models provides guidance for developing diagnostics, and implementation of these diagnostics to the clinical setting, in turn, provides data for refining the models. In this review, we introduce multi-scale and multi-physical models for understanding disease development, progression, and designing clinical interventions. We begin with multi-scale models of cardiac electrophysiology and mechanics for diagnosis, clinical decision support, personalized and precision medicine in cardiology with examples in arrhythmia and heart failure. We then introduce computational models of vasculature mechanics and associated mechanical forces for understanding vascular disease progression, designing clinical interventions, and elucidating mechanisms that underlie diverse vascular conditions. We conclude with a discussion of barriers that must be overcome to provide enhanced insights, predictions, and decisions in pre-clinical and clinical applications.

Effect of Vitamins C and E on Endothelial Function in Type 1 Diabetes Mellitus

BACKGROUND/OBJECTIVES

Endothelial dysfunction due to hyperglycemia-induced oxidative damage is an important predictor of future cardiovascular risk in patients with type 1 diabetes mellitus (T1DM) and is present in adolescent T1DM. We hypothesized that combined treatment with the antioxidant vitamins C and E might improve endothelial function (EF) and other biochemical risk factors in adolescents with T1DM.

SUBJECTS/METHODS

Open-label antioxidant supplementation was given for six weeks with endpoint measurements collected at baseline and study completion. Endpoints measured included EF and plasma measurements of biochemical endothelial risk.

RESULTS

Two males and 7 females were studied. Mean age was 12.9 ± 0.9 yrs; mean T1DM duration was 5.5 ± 2.5 yrs; mean BMI was 22.1 ± 3.8 kg/m(2); and mean hemoglobin A1c was 9.3 ± 1.1%. No differences were found for EF, high sensitivity CRP, total antioxidant capacity, adiponectin, or endothelial progenitor cells (EPCs) between before and after combined vitamin C and E therapy.

CONCLUSIONS

Our negative study results do not support previous findings of decreased oxidative damage, improved endothelial function, and increased vascular repair capacity with antioxidant therapy. Longer term studies may be needed to determine the effects, if any, of combined antioxidant therapy on EPCs, EF, and markers of micro- and macrovascular complications in T1DM.

Exercise-induced vasodilation in healthy males: A marker of reduced endothelial function

OBJECTIVES

Reduced arterial vasodilatatory capacity is a marker of coronary heart disease. The aim was to investigate if the difference between the vasodilatory response before and after exercise, as assessed by non-invasive methodology, is related to endothelial and inflammatory biomarkers.

DESIGN

Post-ischemic hyperemia after 5 min of arterial occlusion was examined before and after a bicycle test with strain-gauge plethysmography (measuring peak reactive hyperemia in the forearm) and peripheral arterial tonometry (PAT hyperemia ratio: measuring pulse waves in the index finger relative to the contra-lateral index finger) in 30 healthy males. A low PAT hyperemia ratio or a low peak reactive hyperemia reflects endothelial dysfunction. Inflammatory and endothelial biomarkers were assessed.

RESULTS

A low peak reactive hyperemia and a low PAT hyperemia ratio before the bicycle test was associated with a high percentage increase in peak reactive hyperemia after exercise (r = - 0.68, p < 0.001; r = - 0.35, p = 0.06, respectively). Asymmetric dimethylarginine and interleukin-10 were associated with the percentage increase in peak reactive hyperemia in multiple linear regression analyses (β: 165 (confidence interval [CI], 34-296), p = 0.02; β: 19 (CI, - 0.5-39), p = 0.06, respectively).

CONCLUSIONS

The difference in the vasodilatory response before and after exercise, as assessed by non-invasive methodology, is related to endothelial and inflammatory biomarkers in healthy males.

Assessment of endothelial function. History, methodological aspects, and clinical perspectives

In 1986, endothelial function was measured for the first time in patients with atherosclerotic coronary arteries. Since then, several methods for assessment of endothelial function, such as endothelium-dependent vasodilation induced by intra-arterial infusion of vasoactive agents using coronary angiography, Doppler flow guide wire, mercury-filled Silastic strain-gauge plethysmography, flow-mediated vasodilation, reactive hyperemia-peripheral arterial tonometry, and vascular response using an oscillometric method have been performed in humans. This review focuses on the assessment of endothelial function, including measurement history, methodological issues, and clinical perspectives.

Endothelial dysfunction after non-cardiac surgery: a systematic review

BACKGROUND

More than 50% of patients with increased troponin levels after non-cardiac surgery have an impaired endothelial function pre-operatively. Non-invasive markers of endothelial function have been developed for the assessment of endothelial dysfunction. The aim of this paper was to systematically review the literature to evaluate the association between non-cardiac surgery and non-invasive markers of endothelial function.

METHODS

A systematic search was conducted in MEDLINE, EMBASE and Cochrane Library Database according to the PRISMA guidelines. Endothelial dysfunction was described only with non-invasive measurements done both pre- and post-operatively and published in English. All types of non-cardiac surgery and both men and women of all ages were included.

RESULTS

We found 1722 eligible studies in our search, and of these, five studies fulfilled our inclusion and exclusion criteria. Endothelial function was disturbed in patients after non-cardiac surgery. Three studies found a significant decrease in the endothelial function immediately after surgery (2 and 24 h post-operatively). Two studies found that patients with previous endothelial dysfunction and scheduled for surgery (renal transplantation and vascular surgery respectively) had an improvement in endothelial dysfunction 1 month after surgery.

CONCLUSION

Endothelial function changes in relation to surgery. Assessment of endothelial function by non-invasive measures has the potential to guide clinicians in the prevention or treatment of post-operative myocardial damage.

Effects of glucose control and variability on endothelial function and repair in adolescents with type 1 diabetes

Background. Endothelial dysfunction and increased inflammation are precursors of cardiovascular disease in type 1 diabetes (T1D) and occur even in adolescents with T1D. The goal of this study was to determine the relationship of endothelial dysfunction to various measures of glycemia. Research Design and Methods. Forearm blood flow (FBF, venous occlusion plethysmography) was measured before and after 5 min of upper arm vascular occlusion in 17 adolescents with uncomplicated type 1 diabetes. Endothelial function was assessed as postocclusion FBF and forearm vascular resistance (FVR, mean arterial pressure/FBF). Fasting glucose, 72 hour mean glucose and standard deviation from continuous glucose monitoring, hemoglobin A1c, and hemoglobin A1c by duration area under the curve were used to assess immediate, short-term, and intermediate- and long-term glycemia. Results. Postocclusion FBF (r = −0.53, P = 0.030) negatively correlated and postocclusion FVR positively correlated (r = 0.52, P = 0.031) with hemoglobin A1c levels. FVR was positively associated with log 3 day mean glucose (r = 0.55, P = 0.027). Postocclusion FBF (2.8 ± 1.1 versus 3.4 ± 0.5 mL/dL/min, mean ± SE, P = 0.084) tended to be lower and FVR (31.4 ± 10.4 versus 23.9 ± 4.4 mmHg dL min/mL, P = 0.015) was significantly higher in subjects with hemoglobin A1c above the median (8.3%) compared to those with lower hemoglobin A1c levels. Conclusions. These results demonstrate that poor intermediate-term glycemic control is associated with impaired endothelial function.

The role of noninvasive and invasive diagnostic imaging techniques for detection of extra-cranial venous system anomalies and developmental variants

The extra-cranial venous system is complex and not well studied in comparison to the peripheral venous system. A newly proposed vascular condition, named chronic cerebrospinal venous insufficiency (CCSVI), described initially in patients with multiple sclerosis (MS) has triggered intense interest in better understanding of the role of extra-cranial venous anomalies and developmental variants. So far, there is no established diagnostic imaging modality, non-invasive or invasive, that can serve as the "gold standard" for detection of these venous anomalies. However, consensus guidelines and standardized imaging protocols are emerging. Most likely, a multimodal imaging approach will ultimately be the most comprehensive means for screening, diagnostic and monitoring purposes. Further research is needed to determine the spectrum of extra-cranial venous pathology and to compare the imaging findings with pathological examinations. The ability to define and reliably detect noninvasively these anomalies is an essential step toward establishing their incidence and prevalence. The role for these anomalies in causing significant hemodynamic consequences for the intra-cranial venous drainage in MS patients and other neurologic disorders, and in aging, remains unproven.

Leptin and endothelial function in the elderly: the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study

BACKGROUND

Leptin levels are elevated in obese humans. Several studies have shown an association between hyperleptinemia and development of atherosclerosis and cardiovascular disease (CVD), but the relationship between leptin and vascular function remains unclear.

AIM

To evaluate associations between circulating plasma leptin and measures of vascular function in a large sample of elderly individuals from the community.

METHODS

This cross-sectional study included 1016 subjects aged 70 (50% women) from the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS). The invasive technique forearm plethysmography with intra-arterial infusions of acetylcholine and sodium nitroprusside was used for estimation of endothelial dependent vasodilatation (EDV) and endothelial independent vasodilatation (EIDV), respectively, in resistance arteries, and the non-invasive technique ultrasound assessed flow mediated vasodilation (FMD) in conduit arteries. The aortic augmentation index (AoAI), a surrogate measure of arterial stiffness, was evaluated by pulse wave analysis. Associations of vascular function, arterial stiffness and blood pressure with leptin were explored.

RESULTS

In sex-adjusted models, high levels of leptin were inversely associated with EDV and EIDV. These associations remained after stratification for sex, traditional risk factors of CVD and insulin resistance, but were attenuated after taking a measure of obesity (body mass index) into account. In addition, leptin associated with arterial stiffness and systolic and diastolic blood pressure.

CONCLUSION

Hyperleptinemia associated inversely with vasodilatation in resistance arteries. Furthermore, hyperleptinemia associated with arterial stiffness and hypertension. These associations were attenuated after adjusting for body mass index suggesting that leptin may be the mediator between obesity and impaired vascular function.

Ascorbic acid blocks hyperglycemic impairment of endothelial function in adolescents with type 1 diabetes

OBJECTIVE

To determine whether acute ascorbic acid infusions alter the effect of hyperglycemia on endothelial function in adolescents with type 1 diabetes.

RESEARCH DESIGN AND METHODS

The forearm blood flow (FBF) reactive hyperemic response to 5 min of upper arm occlusion was studied in eight adolescents with type 1 diabetes during euglycemic and hyperglycemic insulin clamp (40 mU/m2/min) with and without ascorbic acid infusion (3 mg/min).

RESULTS

The ratio of post- to preocclusion FBF decreased during hyperglycemia without ascorbic acid (p = 0.013), but did not change during hyperglycemia with ascorbic acid. The changes during hyperglycemia were different between the two studies (p = 0.038). Similar results were found when the percent change in forearm vascular resistance following occlusion was assessed.

CONCLUSIONS

These results indicate that antioxidant treatment with ascorbic acid blocks acute hyperglycemic impairment of endothelial function in adolescents with type 1 diabetes.

A proposed reductionist solution to address the methodological challenges of inconsistent reflexology maps and poor experimental controls in reflexology research: a discussion paper

Reflexology is a complex massage intervention, based on the concept that specific areas of the feet (reflex points) correspond to individual internal organs within the body. Reflexologists trained in the popular Ingham reflexology method claim that massage to these points, using massage techniques unique to reflexology, stimulates an increase in blood supply to the corresponding organ. Reflexology researchers face two key methodological challenges that need to be addressed if a specific treatment-related hemodynamic effect is to be scientifically demonstrated. The first is the problem of inconsistent reflexology foot maps; the second is the issue of poor experimental controls. This article proposes a potential experimental solution that we believe can address both methodological challenges and in doing so, allow any specific hemodynamic treatment effect unique to reflexology to experimentally reveal itself.

Hyperglycemia increases muscle blood flow and alters endothelial function in adolescents with type 1 diabetes

Alterations of blood flow and endothelial function precede development of complications in type 1 diabetes. The effects of hyperglycemia on vascular function in early type 1 diabetes are poorly understood. To investigate the effect of hyperglycemia on forearm vascular resistance (FVR) and endothelial function in adolescents with type 1 diabetes, FVR was measured before and after 5 minutes of upper arm arterial occlusion using venous occlusion plethysmography in (1) fasted state, (2) euglycemic state (~90 mg/dL; using 40 mU/m²/min insulin infusion), and (3) hyperglycemic state (~200 mg/dL) in 11 adolescents with type 1 diabetes. Endothelial function was assessed by the change in FVR following occlusion. Seven subjects returned for a repeat study with hyperglycemia replaced by euglycemia. Preocclusion FVR decreased from euglycemia to hyperglycemia (P = 0.003). Postocclusion fall in FVR during hyperglycemia was less than during euglycemia (P = 0.002). These findings were not reproduced when hyperglycemia was replaced with a second euglycemia. These results demonstrate that acute hyperglycemia causes vasodilation and alters endothelial function in adolescents with type 1 diabetes. In addition they have implications for future studies of endothelial function in type 1 diabetes and provide insight into the etiology of macrovascular and microvascular complications of type 1 diabetes.

A review of the evidence for the effects of total dietary fat, saturated, monounsaturated and n-6 polyunsaturated fatty acids on vascular function, endothelial progenitor cells and microparticles

Vascular dysfunction is recognised as an integrative marker of CVD. While dietary strategies aimed at reducing CVD risk include reductions in the intake of SFA, there are currently no clear guidelines on what should replace SFA. The purpose of this review was to assess the evidence for the effects of total dietary fat and individual fatty acids (SFA, MUFA and n-6 PUFA) on vascular function, cellular microparticles and endothelial progenitor cells. Medline was systematically searched from 1966 until November 2010. A total of fifty-nine peer-reviewed publications (covering fifty-six studies), which included five epidemiological, eighteen dietary intervention and thirty-three test meal studies, were identified. The findings from the epidemiological studies were inconclusive. The limited data available from dietary intervention studies suggested a beneficial effect of low-fat diets on vascular reactivity, which was strongest when the comparator diet was high in SFA, with a modest improvement in measures of vascular reactivity when high-fat, MUFA-rich diets were compared with SFA-rich diets. There was consistent evidence from the test meal studies that high-fat meals have a detrimental effect on postprandial vascular function. However, the evidence for the comparative effects of test meals rich in MUFA or n-6 PUFA with SFA on postprandial vascular function was limited and inconclusive. The lack of studies with comparable within-study dietary fatty acid targets, a variety of different study designs and different methods for determining vascular function all confound any clear conclusions on the impact of dietary fat and individual fatty acids on vascular function.

[Effects of two methods of heat therapy on the acute vascular response and hemodynamics in healthy subjects]

OBJECTIVE

Recently, non-pharmacological resources to relieve pain like hot packs and ultrasound (US) have become common in clinical practice. However, little experimental evidence is available about the possible mechanisms through which these methods bring about pain relief. We aimed to determine the effects of hot packs and US on the acute vascular response and on hemodynamic parameters in healthy subjects.

MATERIALS AND METHODS

We conducted an experimental study in 20 healthy subjects (10 men and 10 women; mean age, 22.54±1.70 years). The two interventions were randomly applied: a) hot packs (n=10): 15min at 60°C and b) US (n=10): 15min at 1Mhz. Before and after each intervention, the following vascular parameters were measured in the brachial artery using Doppler ultrasonography with a 7MHz probe: arterial compliance, elastic modulus, beta stiffness index, systolic and diastolic arterial diameters, systolic flow velocity and diastolic flow velocity, systolic/diastolic ratio, resistance index, and pulsatility index. The following hemodynamic parameters were monitored: heart rate and blood pressure (systolic, diastolic, and mean).

RESULTS

After the application of hot packs, we observed changes in diastolic flow velocity and in the pulsatility index (P<05). After the application of US, we observed changes in diastolic flow velocity, systolic/diastolic ratio, resistance index, and arterial compliance (P<05). No changes in hemodynamic parameters were observed after either intervention.

CONCLUSIONS

Applying hot packs or US modifies the physiology of the vascular system but does not affect hemodynamic parameters in healthy subjects.

Big mitogen-activated protein kinase 1 protects cultured rat aortic smooth muscle cells from oxidative damage

Oxidative stress is considered a major mediator of arteriosclerosis. In vascular smooth muscle cells, oxidative stress-induced cell death (including apoptosis) is probably related to arterial calcification in arteriosclerosis. Big mitogen-activated protein kinase-1 / extracellular signal-regulated kinase 5 (BMK1/ERK5) is a newly identified member of the mitogen-activated protein kinases family. Like Src tyrosine kinase, BMK1/ERK5 is known to be sensitive to oxidative stress; however, its pathophysiological significance is poorly understood. In this study, we investigated the involvement of BMK1 and Src in H(2)O(2)-induced cell death using cultured rat aortic smooth muscle cells (RASMCs). Cell apoptosis was evaluated by using the TdT-mediated dUTP nick end labeling (TUNEL) method, and BMK1 and Src activities were determined by Western blotting. The main results are as follows: 1) BMK1 and Src were activated by H(2)O(2) in a time- and concentration-dependent manner in RASMCs; 2) BMK1 activation by H(2)O(2) was attenuated both in Src-knockdown RASMCs and in RASMCs pretreated with 4-amino-5-(4-chloro-phenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2), a Src family kinases inhibitor; and 3) H(2)O(2)-induced cell death was increased in BMK1- and Src-knockdown RASMCs as well as in PP2-treated RASMCs. These findings suggested that Src and BMK1 may play defensive and resistive roles against oxidative stress-induced death in RASMCs.

The vascular endothelium masks the persistent inhibition of rat thoracic arterial tone induced by S-nitrosoglutathione

AIM

In endothelium-denuded arteries, the nitric oxide (NO) donor S-nitrosoglutathione (GSNO) induced a persistent hypo-reactivity to vasoconstrictors, and low-molecular weight thiols such as N-acetyl cysteine (NAC) produced a relaxant effect. These effects were attributed to the formation of vascular NO stores. In arteries with a functional endothelium, such long-lasting effects on arterial tone have not been well characterised. In this study, we proposed to examine the possibility of storing exogenous NO when the vascular endothelium is still able to produce its own NO.

METHODS

For this purpose, changes in isometric tension of isolated arteries were assessed in organ chambers, and nitrosothiol formation was characterised by confocal microscopy.

RESULTS

In rat aortic rings with endothelium pre-exposed to GSNO, the contractile response to norepinephrine (NE) was not attenuated in comparison with control rings, but NAC induced a relaxant effect. However, an attenuation of the response to NE was observed in GSNO-exposed, intact aortic rings after inhibition of NO synthase by N(ω)-nitro-L-arginine methylester (L-AME) or in GSNO-denuded rings. The relaxing effects of NAC were due to the mobilisation of NO from nitrosothiols after nitrosylation of protein SH residues. Moreover, the hypo-reactivity to NE and the relaxant effect of NAC were abolished by 1H-[1,2,4] oxadiazolo(4,3-a)quinoxalin-1-one (ODQ), an inhibitor of soluble guanylyl cyclase, and partially by the K+-sensitive channel inhibitor tetra-ethyl-ammonium (TEA).

CONCLUSION

These data show that endothelium-derived NO masked the persistent effect of GSNO in rat thoracic aorta. However, the ability of GSNO to form releasable NO stores without altering the vascular tone can be particularly useful in preventing endothelial dysfunction in which NO formation decreases.

Milk casein-derived tripeptides, VPP and IPP induced NO production in cultured endothelial cells and endothelium-dependent relaxation of isolated aortic rings

Milk casein-derived tripeptides, valyl prolyl proline (VPP), and isoleucyl prolyl proline (IPP) inhibit angiotensin-converting enzyme (ACE) and both fermented milk and proteolytic hydrolysates of milk casein containing these peptides exert blood pressure-lowering effects in animals and humans. On the top of these results, we have recently reported that the hydrolysate of milk casein containing both VPP and IPP improved the vascular endothelial function of subjects with stage I hypertension, enforcing us to elucidate the mechanism of the improvement of endothelial dysfunction by these peptides. For this purpose, we examined the effect of VPP and IPP on induction of nitric oxide (NO) production using cultured vascular endothelial cells and isolated arterial vessels. When both VPP and IPP were added to the medium of cultured endothelial cells at final concentrations of more than 100 nmol/l, the NO(x) (NO(2) and NO(3)) concentration in the medium was significantly higher than that of the control. Moreover, both VPP and IPP induced endothelium-dependent relaxation of isolated aortic rings, and these effects were inhibited by NO synthase inhibitors, K channel inhibitors, and bradykinin B2 receptor antagonists. These lines of results suggested that both VPP and IPP induced production of vasodilative substances including NO.

Renal dysfunction impairs circadian variation of endothelial function in patients with essential hypertension

Some cardiovascular disorders disturb circadian variation of endothelial function. We investigated whether deterioration of renal function alters circadian variation of endothelial function in patients with hypertension. Endothelial function was assessed by the peak forearm blood flow (FBF) response to reactive hyperemia, and 24-hour ambulatory blood pressure monitoring was performed in 25 patients with essential hypertension (61 ± 17 years). Relationships among renal function, 24-hour blood pressure, and endothelial function were analyzed. The ratio of nighttime to daytime mean arterial pressure was inversely correlated with estimated glomerular filtration rate (eGFR) (r = -0.43, P = .03). The FBF response to reactive hyperemia examined at 21:00, but not at 6:30 or 11:30, was significantly correlated with eGFR (r = 0.44, P = .03). Furthermore, the ratio of FBF response measured at 21:00 to that measured at 6:30 was independently correlated with eGFR (β = 0.47, P = .02). Renal dysfunction is associated with the derangement of circadian variation of both endothelial function and blood pressure. Nocturnal blood pressure is elevated, and evening endothelial function deteriorates in parallel with a decline in renal function in hypertensive patients.

Parathyroid Hormone's Acute Effect on Vasodilatory Function

Parathyroid hormone (PTH) seems to affect the risk of cardiovascular disease. The aim of the present study was to investigate PTH's acute effect on endothelial vasodilatory function in forearm resistance vessels. Ten healthy subjects underwent forearm venous occlusion plethysmography. We measured forearm blood flow at baseline and at a stable, locally increased PTH level after intra-arterial infusion of metacholine and nitroprusside. The contralateral arm served as a control. Ionized calcium (Ca++) and PTH values were normal in all subjects at baseline (1.26 ± 0.02 mM/L, 3.6 ± 1.2 pM/L). After 30 minutes of PTH infusion, the PTH level increased in the active arm (13.8 ± 4.0 pM/L P < 0.01), while the Ca++ level was unchanged (1.25 ± 0.04; mM/L). Both the PTH and the Ca++ level in the contralateral arm remained unchanged, which indicates no systemic influence. The endothelial-dependent vasodilation was inversely correlated to the Ca++ level at baseline (r = -0.75, P < 0.05) and after PTH infusion (r = -0.68, P < 0.05). The vasodilatory function was not affected during PTH-infusion.

Endothelial dysfunction, measured by reactive hyperaemia using strain-gauge plethysmography, is an independent predictor of adverse outcome in heart failure

AIMS

In congestive heart failure (CHF), arterial response is regulated by endothelial molecules. The aim of this study was to evaluate whether endothelial dysfunction (ED) was a predictor of outcome in a cohort of patients with heart failure.

METHODS AND RESULTS

Endothelial function was assessed in 242 patients with CHF by forearm reactive hyperaemia measured with intermittent venous occlusion plethysmography using a mercury strain gauge. The main endpoints were: 'total events' (death, heart attack, angina, stroke, NYHA class IV, or hospitalization due to heart failure) analysed using Cox regression for repeated events and 'death'. Patients were followed-up for 5 years. Post-hyperaemia forearm blood flow (PHFABF) was an independent predictor of total events [P = 0.01; hazard ratio [Exp(B)] 0.665, standard error (SE) 0.182]. Risk stratification by basal forearm blood flow (BFABF) showed that patients with basal blood flow above the median (3.03 mL min(-1) 100 mL(-1)) benefited from an increase in PHFABF, whereas in patients with a BFABF below the median, the increase in PHFABF did not diminish the risk of events. There was no relation between variations in PHFABF and death.

CONCLUSION

Post-hyperaemia forearm blood flow, as a measure of ED, is an independent predictor of major events in patients with CHF. A BFABF below the median is more predictive of an increased risk of complications.

Insulin and non-insulin mediated vasodilation and glucose uptake in patients with type 2 diabetes

AIMS

The objective was to re-examine endothelial function, insulin mediated vasodilation and glucose extraction in the forearm of patients with type 2 diabetes (T2DM) and matched control subjects (CON) to investigate whether blood flow impairments result from diabetes per se or from concurrent disease.

METHODS

18 subjects (10 with T2DM, 8 CON) had graded brachial artery infusions of endothelial dependent (acetylcholine: 15, 30, 60 microg/min), endothelial independent (sodium nitroprusside: 1, 3, 10 microg/min) and partially endothelial mediated (adenosine: 50, 150, 500 microg/min) vasodilators. The protocol was repeated during a hyperinsulinemic clamp. Forearm blood flow and glucose extraction were measured at each dose of vasodilator (with/without insulin). Measurements were also taken in the control arm, reflecting systemic insulin infusion only.

RESULTS

Non-insulin mediated increases in bulk forearm blood flow were similar in T2DM and CON. However, insulin mediated forearm blood flow responses and glucose extraction were lower in T2DM versus CON.

CONCLUSION

The vasodilatory effect of insulin is impaired in T2DM although bulk flow capacity is maintained. Insulin mediated glucose extraction is reduced during concomitant maximal stimulation of forearm blood flow with endothelial-dependent vasodilators, despite maintaining flow. This is consistent with previous work that associates T2DM with impaired insulin mediated capillary recruitment.

Ramipril improves oxidative stress-related vascular endothelial dysfunction in db/db mice

Endothelial dysfunction often precedes Type 2 diabetes-associated cardiovascular complications. One important cause of endothelial dysfunction is oxidative stress, which can lead to reduced nitric oxide (NO) bioavailability. In this study, we examined the effects of ramipril (an angiotensin-converting enzyme inhibitor, ACEI) on reactive oxygen species (ROS) production and endothelium-dependent vasodilation using a Type 2 diabetic (db/db) murine model. Plasma concentration of 8-isoprostane ([8-isoP]) was measured and used as an indication of the amount of ROS production. Six weeks of ramipril (10 mg/kg/day) treatment significantly reduced [8-isoP] and improved acetylcholine(ACh)-induced vasodilation in db/db mice without altering responses in wild-type (WT) mice. Responsiveness of smooth muscle cells to NO, assessed by sodium nitroprusside-induced vasodilation, was not different between db/db and WT mice regardless of ramipril or vehicle treatment. Our results suggest that ramipril specifically improved endothelium-dependent vasodilation in Type 2 diabetic mice, possibly by reducing ROS levels.

Haptoglobin genotype and endothelial function in diabetes mellitus: a pilot study

Endothelial function (EnF) is impaired in patients with diabetes mellitus (DM) due in large part to an increase in oxidative stress. Haptoglobin (Hp) is a potent antioxidant protein which is encoded by two different alleles (1 and 2) with the Hp 1 protein being a superior antioxidant to the Hp 2 protein. We hypothesized that DM individuals with the Hp 2-2 genotype would have greater endothelial dysfunction as compared to DM individuals with the Hp 1-1 genotype. We studied EnF in 16 Hp 2-2, 14 Hp 1-1 DM individuals and 14 healthy subjects. DM patients' groups were matched in terms of age, cardiovascular risk factors and metabolic characteristics. EnF was assessed using post-ischemic reactive hyperemia and strain gauge plethysmography and expressed either as the maximal flow after the ischemic period or as the area under the flow-time curve (AUC). We showed that EnF indices, AUC and maximal flow, were also higher in the healthy and Hp 1-1 groups compared with Hp 2-2 genotype group (615 +/- 60 and 600 +/- 40 vs. 450 +/- 50 ml dl(-1), 29 +/- 2.6 and 25 +/- 3 vs. 14 +/- 1.8 ml min(-1) dl(-1), P < 0.003 and P < 0.05, for AUC and maximal flow, one-way ANOVA, respectively). We concluded that Hp 2-2 diabetic patients had a worse EnF than controls and Hp 1-1 diabetic subjects.

A diet enriched with mackerel (Scomber scombrus)-derived products improves the endothelial function in a senior population (Prevención de las Enfermedades Cardiovasculares: Estudio Santoña--PECES project)

BACKGROUND

Regular consumption of fish reduces cardiovascular risks. Here, we investigate if the consumption of products with mackerel (Scomber scombrus) with 8.82 g of eicosapentaenoic acid (EPA) + docosahexaenoic acid (DHA) content per 100 g of product improves parameters of endothelial function in a controlled population.

MATERIALS AND METHODS

Subjects maintained a 12-week diet with products with mackerel. The population consisted of 58 senior subjects (12 withdrawals, 25 women), aged 82.08 +/- 8.13 years (Group A). Twenty-three senior subjects (13 women) on a regular diet were used as the control group (Group B). Subjects of Group A received 57 portions throughout 12 weeks (four to five portions a week of products with a mean EPA + DHA content of 2.5 g a day). A continuous follow-up and a final evaluation were performed to determine the level of consumption. Plasma samples were stored at -70 degrees C for a biochemical study. Endothelial function was analysed by reactive hyperemia with a mercury strain gauge plethysmography with measurement of blood flow in the forearm, both baseline and at the end of the 12-week diet.

RESULTS

Endothelium-dependent vasodilatation significantly increased in Group A subjects (P < 0.001). No changes were found in Group B. The subgroup analyses showed that improvements were produced in Group A subjects without cardiovascular disease (P < 0.001). Nitrites/nitrates and von Willebrand factor plasma concentrations were higher in participants after the 12-week diet.

CONCLUSIONS

The consumption of mackerel meat products improves endothelium-dependent, flow-mediated vasodilatation in a senior population. This finding might explain some of the cardioprotective effects of fish consumption.

Capillary rarefaction in treated and untreated hypertensive subjects

This study aimed to determine if capillary rarefaction is detectable and associated with endothelial dysfunction in persons with mild systolic blood pressure (SBP) elevation. Capillary density and endothelial function were quantified for 150 nondiabetic participants, grouped by blood pressure (BP) as normotensive, untreated high BP, and treated high BP. Structural capillary rarefaction measures were not different between the three groups. Functional capillary rarefaction measures were significantly lower in both high BP groups compared to normotensives, and correlated inversely with endothelial function. The study findings indicate that the hypertensive vascular pathologic process is already underway at modest levels of blood pressure elevation.

Impaired endothelial function and insulin action in first-degree relatives of patients with type 2 diabetes mellitus

First-degree relatives (FDR) of patients with type 2 diabetes mellitus are at increased risk of developing type 2 diabetes mellitus. We studied if endothelial dysfunction of the resistance vessels is present and may coexist with metabolic insulin resistance in FDR. Male FDR (n = 13; 26 +/- 1 years; body mass index, 25 +/- 1 kg m(2) [mean +/- SEM]) and matched control subjects (CON) (n = 22; 25 +/- 1 years; body mass index, 24 +/- 1 kg m(2)) were studied by hyperinsulinemic (40 mU min(-1)m(-2)) isoglycemic clamp combined with brachial arterial and deep venous catheterization of the forearm. Forearm blood flow (FBF) was measured by venous occlusion plethysmography upon stimulation with systemic hyperinsulinemia (291 +/- 11 pmol/L, pooled data from both groups) and upon intraarterial infusion of adenosine (ADN) and acetylcholine (ACH) +/- hyperinsulinemia. Forearm blood flow response to ADN and ACH was less in FDR vs CON (P < .05); systemic hyperinsulinemia added to the FBF effect of ADN in CON (P < .05) but not in FDR. In addition, FDR demonstrated impaired FBF to hyperinsulinemia (2.1 +/- 0.2 vs 4.0 +/- 0.6 mL 100 mL(-1) min(-1)) in FDR and CON, respectively (P < .05). Both M-value (5.0 +/- 0.7 vs 7.0 +/- 0.5 mg min(-1) kg(-1)) and forearm glucose clearance (0.6 +/- 0.1 vs 1.4 +/- 0.4 mL 100 mL(-1)min(-1)) were diminished in FDR compared with CON (all P < .05). FDR demonstrated endothelial dysfunction of the resistance vessels in addition to impaired insulin-stimulated increase in bulk flow. Moreover, FDR demonstrated whole-body insulin resistance as well as decreased basal and insulin-stimulated forearm glucose uptake. It remains to be established whether FDR also demonstrate impaired insulin-stimulated microvascular function.

Racial differences in central blood pressure and vascular function in young men

Young African-American men have altered macrovascular and microvascular function. In this cross-sectional study, we tested the hypothesis that vascular dysfunction in young African-American men would contribute to greater central blood pressure (BP) compared with young white men. Fifty-five young (23 yr), healthy men (25 African-American and 30 white) underwent measures of vascular structure and function, including carotid artery intima-media thickness (IMT) and carotid artery β-stiffness via ultrasonography, aortic pulse wave velocity, aortic augmentation index (AIx), and wave reflection travel time (Tr) via radial artery tonometery and a generalized transfer function, and microvascular vasodilatory capacity of forearm resistance arteries with strain-gauge plethysmography. African-American men had similar brachial systolic BP (SBP) but greater aortic SBP ( P < 0.05) and carotid SBP ( P < 0.05). African-American men also had greater carotid IMT, greater carotid β-stiffness, greater aortic stiffness and AIx, reduced aortic Tr and reduced peak hyperemic, and total hyperemic forearm blood flow compared with white men ( P < 0.05). In conclusion, young African-American men have greater central BP, despite comparable brachial BP, compared with young white men. Diffuse macrovascular and microvascular dysfunction manifesting as carotid hypertrophy, increased stiffness of central elastic arteries, heightened resistance artery constriction/blunted resistance artery dilation, and greater arterial wave reflection are present at a young age in apparently healthy African-American men, and conventional brachial BP measurement does not reflect this vascular burden.

Vasodilation in vasovagal syncope and the effect of water ingestion

Abnormal (increased, but also decreased) vasodilative responses have been observed in patients with vasovagal syncope (VVS). The objective was to assess reactive vasodilation in supine patients with VVS and its relation to severity of the syndrome. Reactive vasodilation was also assessed after a simple therapeutic intervention (water drinking). Thirty-four patients were studied, all with recurrent VVS and a recent positive head-up tilt test result. Seventeen matched healthy subjects served as controls. Venous occlusion plethysmography was used to assess forearm blood flow (FBF) and forearm vascular resistance resistance (1) at rest and (2) during reactive hyperemia. Clinical severity of the syndrome was related to the intensity and duration of the vasodilative reflex. The same plethysmographic measurements were repeated 60 minutes after drinking 500 ml of water. Before water drinking, no difference was observed between groups in baseline measurements. However, duration of hyperemia was longer in patients (p <0.05) and was related to the duration of the previous positive tilt test (r = -0.69, p <0.05) and total number of each patient's symptomatic vasovagal episodes (r = 0.49, p <0.05). After water ingestion, baseline FBF decreased in patients (p <0.05) and remained stable in controls. In patients, duration of hyperemia decreased to normal values. Hyperemic FBF remained similar between groups. In conclusion, increased reactive vasodilative reflexes were observed in patients with VVS. They seemed to be of significant pathophysiologic significance. Water drinking can normalize them for >or=60 minutes.

Lumped parameter thermal model for the study of vascular reactivity in the fingertip

Vascular reactivity (VR) denotes changes in volumetric blood flow in response to arterial occlusion. Current techniques to study VR rely on monitoring blood flow parameters and serve to predict the risk of future cardiovascular complications. Because tissue temperature is directly impacted by blood flow, a simplified thermal model was developed to study the alterations in fingertip temperature during arterial occlusion and subsequent reperfusion (hyperemia). This work shows that fingertip temperature variation during VR test can be used as a cost-effective alternative to blood perfusion monitoring. The model developed introduces a function to approximate the temporal alterations in blood volume during VR tests. Parametric studies are performed to analyze the effects of blood perfusion alterations, as well as any environmental contribution to fingertip temperature. Experiments were performed on eight healthy volunteers to study the thermal effect of 3 min of arterial occlusion and subsequent reperfusion (hyperemia). Fingertip temperature and heat flux were measured at the occluded and control fingers, and the finger blood perfusion was determined using venous occlusion plethysmography (VOP). The model was able to phenomenologically reproduce the experimental measurements. Significant variability was observed in the starting fingertip temperature and heat flux measurements among subjects. Difficulty in achieving thermal equilibration was observed, which indicates the important effect of initial temperature and thermal trend (i.e., vasoconstriction, vasodilatation, and oscillations).

A relationship between insulin sensitivity and vasodilation in women with a history of preeclamptic pregnancy

Women with a history of preeclampsia are characterized by vascular dysfunction and an increased risk of cardiovascular disease. In the present study we investigated whether insulin sensitivity is decreased in women with previous preeclampsia and whether it is associated with endothelium-dependent and/or -independent vasodilation and/or features of metabolic syndrome. Twenty-eight nonobese women with previous severe preeclampsia and 20 women with a previous normotensive pregnancy were studied 5 to 6 years after the index pregnancy. Vasodilation was measured by venous occlusion plethysmography after intra-arterial infusions of sodium nitroprusside and acetylcholine and insulin sensitivity by the intravenous glucose tolerance test using the minimal model technique. The women were tested for lipid profile, inflammatory status and endothelial activation. Insulin sensitivity did not differ between the groups (P=0.24). Insulin sensitivity correlated positively to endothelium-dependent vasodilation only in the patient group in both low (beta=0.59; P=0.04) and high (beta=0.53; P=0.04) concentrations of acetylcholine and in a high concentration of sodium nitroprusside (beta=0.0007; P=0.006). In multivariate analysis, the waist/hip ratio (P=0.04) and serum triglycerides (P=0.04) had the most effect on insulin sensitivity in the patient group. Gestational weeks at the onset of preeclamptic hypertension (P=0.02) and proteinuria (P=0.02) associated positively with insulin sensitivity together with first-trimester body mass index (P=0.008) and maximum diastolic blood pressure during preeclampsia (P=0.005). The present study indicates a relation between insulin sensitivity with vascular dilatory function in women with previous preeclampsia. Furthermore, early onset preeclampsia correlates with impaired insulin sensitivity later in life.

Health behaviors and endothelial function

An unhealthy lifestyle, including excess caloric intake, lack of exercise, smoking, and excessive alcohol consumption, increases one's risk of developing cardiovascular disease (CVD). However, the exact mechanisms by which these behaviors influence the development and progression of CVD have yet to be determined. Endothelial function (EF) has been shown to be a potent predictor of CVD, yet the effects of health behaviors on EF are not clear. The literature assessing the role of four health behaviors, obesity (a proxy of excess caloric intake), smoking, physical inactivity, and alcohol consumption, on the development of endothelial dysfunction is reviewed. Potential mechanisms through which these behaviors may influence EF are discussed. Smoking, being overweight or obese, and physical inactivity are all associated with decreased EF. A direct causal relationship between these measures and EF is suggested by the fact that improvements in these behaviors leads to parallel improvements in EF. The influence of alcohol consumption is somewhat more contentious, with some studies indicating a dose-response relationship such that those with greater consumption have poor EF. However, other studies have shown that those who drink moderately have the best EF. Although there is a growing body of literature implicating poor health behaviors in the development of endothelial dysfunction, more work is needed to establish the exact mechanisms by which this occurs. To our knowledge, there are no studies that have assessed the impact of multiple health behaviors or the interaction of health behaviors on EF.

Statin Therapy for Vascular Failure

There is increasing evidence that statins reduce cardiovascular events such as coronary artery disease or stroke in hypercholesterolemic patients in both primary and secondary prevention. The striking benefit achieved with statin treatments in patients with a wide range of cholesterol levels cannot be attributed to their cholesterol lowering effect alone. Substantial data has recently accumulated showing that statins exert various effects on multiple targets, namely pleiotropic effects, especially targeting the concept of 'vascular failure', including the improvement of vascular endothelial function, inhibition of vascular smooth muscle cell proliferation and migration, anti-inflammatory actions, anti-oxidative effects or stabilization of vulnerable plaques. These effects have potential in the treatments of coronary artery disease in various settings, such as prevention of its onset as well as its progression, or plaque rupture. Statin therapy should be more extensively applied even in normolipidemic patients if there are additional risk factors such as hypertension, diabetes mellitus, or others. Furthermore, statins may be used to intervene in earlier stage risk conditions such as postprandial hyperlipidemia or hyperglycemia, insulin resistant state, masked hypertension, or metabolic syndrome to further reduce mortality or morbidity of coronary artery disease and heart failure.

Thyroid disease and vascular function

Altered cardiac function in thyroid disease is well recognized and has been extensively investigated, vascular function has however been less well studied in those with thyroid dysfunction. Thyroid hormones, thyroxine (T(4)) and triiodothyronine (T(3)) are important regulators of cardiac function and cardiovascular hemodynamics. The cardiovascular system responds to minimal but persistent changes in circulating thyroid hormone levels producing changes in vascular reactivity and endothelial function. The detection of endothelial dysfunction and/or arterial stiffness allows early identification of individuals at risk as these occur in both patients with risk factors for coronary artery disease and in those with established disease. This may allow treatment to be targeted at high risk individuals with the aim of slowing the progression of vascular disease. The various methods used to assess arterial function are reviewed and the changes demonstrated in human and animal models of thyroid dysfunction.

Impaired endothelial function in healthy African-American adolescents compared with Caucasians

OBJECTIVE

To determine whether African-American adolescents have endothelial dysfunction compared with Caucasians and whether differences are a result of differences in insulin sensitivity calculated from total glucose (S(I)) or secretion.

STUDY DESIGN

Thirty-three Caucasian (13.6 +/- 2.6 years of age; body mass index [BMI] 21.6 +/- 4.4 kg/m2 mean +/- SD) and 25 African-American (13.3 +/- 2.9 years of age; BMI 24.0 +/- 4.4 kg/m2) adolescents were studied. Forearm blood flow (FBF; plethysmography) was measured before and after 5 minutes of arterial occlusion. S(I) and acute insulin response to glucose (AIRG) were measured using intravenous glucose tolerance tests and minimal modeling.

RESULTS

Baseline FBF did not differ between races. Postocclusion FBF was lower in African-Americans (17.2 +/- 1.2 vs 22.6 +/- 1.2 mL/dL/minute, P = .006). AIRG was higher in African-Americans (6050 +/- 940 vs 2410 +/- 30 microU minute/mL, P = .001). Pubertal stage had no effect. S(I) did not differ by race or pubertal stage. In African-Americans, percent fall in FVR following arterial occlusion correlated (r = 0.67, P = .001) with log AIRG. No relationships were found between percent fall in FVR and S(I) in either race.

CONCLUSION

African-American adolescents have decreased endothelial function. This may be a result of increased insulin secretion. Endothelial dysfunction in African-American adolescents may predispose to cardiovascular and type II diabetes.

Assessment of microvascular function by study of the dose–response effects of iontophoretically applied drugs (acetylcholine and sodium nitroprusside)—Methods and comparison with in vitro studies

Current knowledge about vascular function stems mainly from pharmacological in vitro studies using mounted vascular strips on a strain gauge. We know of no paper that has systematically examined the possibility of assessing the conventional dose-response effects of iontophoresis and laser Doppler investigation of vasoactive substances and compared those relations to data obtained from strips mounted on a strain gauge. We used the vasoactive substances acetylcholine (endothelium dependent) and sodium nitroprusside (endothelium independent) and an antagonist (atropine) to enable further investigations in the receptor physiology of iontophoresis. Dose-response curves from the iontophoresis experiments showed close similarity to those obtained by vascular strips mounted on a strain gauge. The coefficient of variation (CV) of the dose-response factors found in iontophoresis (both inter and intra experimental variability) was low. The iontophoretic effective dose of 50% (ED50) for acetylcholine and nitroprusside had only CVs of 25% and 26%, respectively, compared with 71% and 77% for the vascular strips. Acetylcholine-induced response was antagonized by iontophoresis of atropine. Contrary to expectations, this antagonism was not competitive. The results show that iontophoresis in combination with laser Doppler technology produces reproducible and reliable dose-response curves that picture the vascular effects of vasoactive drugs.