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

Comportamento da pressão arterial após exercícios contra-resistência: uma revisão sistemática sobre variáveis determinantes e possíveis mecanismos

A hipotensão pós-exercício (HPE) é um fenômeno com elevada relevância clínica, mas que ainda apresenta aspectos duvidosos em relação às variáveis que podem contribuir para sua manifestação. A dúvida é maior quando o exercício contra-resistência é aplicado com intuito de proporcionar HPE. Nesse sentido, o objetivo deste estudo foi rever algumas variáveis do exercício contra-resistência que podem estar associadas à HPE. Além disso, foram comentados alguns mecanismos fisiológicos possivelmente relacionados com esse efeito. Encontraram-se 14 referências abrangendo o exercício contra-resistência e a HPE. Seis estudos observaram efeito hipotensivo para a pressão arterial sistólica (PAS) e/ou diastólica (PAD) após o exercício contra-resistência. Contudo, foi observado que alguns estudos não identificaram diferenças significativas (p > 0,05) para PAS e PAD (n = 4) ou até relataram aumento significativo (p < 0,05) (PAS ou PAD) (n = 4). Esses resultados discordantes podem estar relacionados ao volume e à intensidade do exercício, assim como o período de monitorização. Contudo, é possível identificar HPE quando se aplica o exercício contra-resistência, tanto em pessoas normotensas quanto hipertensas. Todavia, os mecanismos fisiológicos responsáveis por esse tipo de resposta ainda permanecem obscuros.

Exercise-induced improvement in vasodilatory function accompanies increased insulin sensitivity in obesity and type 2 diabetes mellitus

OBJECTIVE

The present study was undertaken to determine whether improved vasodilatory function accompanies increased insulin sensitivity in overweight, insulin-resistant subjects (OW) and type 2 diabetic patients (T2DM) who participated in an 8-wk exercise training regimen.

DESIGN

Before and after training, subjects had euglycemic clamps to determine insulin sensitivity. Brachial artery catheterization was done on another occasion for measurement of vasodilatory function. A lean, healthy, untrained group was studied as nonexercised controls.

RESULTS

Training increased oxygen consumption (VO2) peak [OW, 29 +/- 1 to 37 +/- 4 ml/kg fat-free mass (FFM).min; T2DM, 33 +/- 2 to 43 +/- 3 ml/kg FFM.min; P < 0.05] and improved insulin-stimulated glucose disposal (OW, 6.5 +/- 0.5 to 7.2 +/- 0.4 mg/kg FFM.min; T2DM, 3.8 +/- 0.3 to 4.2 +/- 0.3 mg/kg FFM.min; P < 0.05) in insulin resistance. OW and T2DM, before training, had decreased acetylcholine chloride (ACh)- and sodium nitroprusside-mediated vasodilation and decreased reactive hyperemia compared with lean controls. Training increased the vasodilatory response to ACh [OW (30 microg ACh/min), 12.2 +/- 3.4 to 19 +/- 4.2 ml/100 g.min; T2DM (30 microg ACh/min), 10.1 +/- 1.5 to 14.2 +/- 2.1 ml/100 g.min; P < 0.05] in both groups without affecting nitroprusside response.

CONCLUSION

Because vasodilatory dysfunction has been postulated to contribute to insulin resistance, the exercise-induced improvement in vasodilatory function may signify changes in the endothelium that could contribute to the improvement in insulin sensitivity observed after aerobic exercise training.

Vascular resistance and endothelial function in cyclosporine-treated lung transplant recipients

The majority of patients undergoing solid organ transplantation develop hypertension, to which vasoconstriction and impaired endothelial function have been suggested to contribute. We compared basal vascular resistance and nitric oxide-mediated endothelial-dependent and independent vasoreactivity between cyclosporine-treated lung transplant recipients and healthy subjects. Forearm blood flow was measured by venous occlusion plethysmography at rest and during acetylcholine, glyceryltrinitrate and N(G)-monomethyl-L-arginine acetate (L-NMMA) infusion in 11 lung transplant recipients 3-5 years after transplantation and in eight healthy subjects. Forearm vascular resistance (FVR) was calculated. Plasma levels of endothelin-1 (ET-1) and von Willebrand factor (vWf) were analysed. Basal vascular resistance was 40% lower in transplant recipients than in healthy subjects (P = 0.021). Endothelial-dependent and independent vasodilation did not differ. Plasma levels of ET-1 and vWf were higher in transplant recipients (P = 0.009 and P < 0.001 respectively). There was a significant correlation between ET-1 levels and FVR in healthy subjects (r = 0.83, P = 0.042), but not in transplant recipients (r = -0.14, P = 0.70). The findings oppose the theory of generalized vasoconstriction and impaired endothelial function in the pathogenesis of hypertension after transplantation. Increased plasma levels of ET-1 do not cause increased FVR in lung transplant recipients.

Vascular failure: A new clinical entity for vascular disease

Atherosclerosis is characterized by the response of the vessel wall to chronic multifactorial injury leading to the formation of atheromatous or fibrous plaques. Endothelial dysfunction represents an initial stage of atherosclerosis. In addition to endothelial dysfunction, smooth muscle dysfunction, metabolic abnormalities of the vessel wall including inflammation, oxidative stress and alterations of neurohormonal balance occur in various stages of atherosclerosis. We now propose a new clinical entity 'vascular failure', defined as the integration of all of these vascular abnormalities. Vascular failure is not an anatomical disease, but rather a comprehensive syndrome of abnormal vascular function. Vascular failure extends from risk factors to established atherosclerotic disease with arterial stenosis, and further to calcification of the vessel wall or serious vascular events that may be caused by plaque rupture and thromboembolic occlusion. We propose aggressive intervention to modify various risk factors, applying to this integrated new entity, vascular failure.

Endothelial dysfunction in rat adjuvant-induced arthritis: vascular superoxide production by NAD(P)H oxidase and uncoupled endothelial nitric oxide synthase

OBJECTIVE

To investigate endothelial function and levels of vascular oxidative stress in rat adjuvant-induced arthritis (AIA), in view of mounting evidence for an association between rheumatoid arthritis (RA) and accelerated vascular disease.

METHODS

Thoracic aortic rings were prepared from AIA and control rats. After preconstriction by norepinephrine, the vasodilatory response to acetylcholine was determined. The amounts of 4-hydroxy-2-nonenal (HNE) and nitrotyrosine in AIA rat aortas were measured by Western blotting. Homogenates of the aortas were incubated with various substrates for superoxide-producing enzymes, and superoxide production was assessed by fluorogenic oxidation of dihydroethidium to ethidium. Expression of endothelial nitric oxide synthase (eNOS) in aortas was examined by real-time reverse transcriptase-polymerase chain reaction and Western blotting. Serum levels of tetrahydrobiopterin (BH4), a critical eNOS cofactor, were determined by high-performance liquid chromatography.

RESULTS

Endothelium-dependent relaxation of the aortic ring was significantly depressed in AIA rats compared with control rats. The amounts of HNE and nitrotyrosine were increased in AIA rat aortas, indicating overproduction of reactive oxygen species. Incubation of AIA rat aorta homogenates with NADH or L-arginine, a substrate of eNOS, resulted in a significant increase in superoxide production. Endothelial NOS was highly expressed in AIA rat aortas. Serum levels of BH4 were significantly lower in AIA. Treatment of AIA with BH4 reversed the endothelial dysfunction, suggesting that its deficiency may contribute to the uncoupling of eNOS.

CONCLUSION

Vascular dysfunction in RA can be partially modeled in animals. NAD(P)H oxidase and uncoupled eNOS are responsible for the increase in vascular oxidative stress, which is likely to be involved in the endothelial dysfunction in AIA.

Butyrylcholinesterase: association with the metabolic syndrome and identification of 2 gene loci affecting activity

BACKGROUND

Plasma cholinesterase activity is known to be correlated with plasma triglycerides, HDL- and LDL-cholesterol, and other features of the metabolic syndrome. A role in triglyceride metabolism has been proposed. Genetic variants that decrease activity have been studied extensively, but the factors contributing to overall variation in the population are poorly understood. We studied plasma cholinesterase activity in a sample of 2200 adult twins to assess covariation with cardiovascular risk factors and components of the metabolic syndrome, to determine the degree of genetic effects on enzyme activity, and to search for quantitative trait loci affecting activity.

METHODS AND RESULTS

Cholinesterase activity was lower in women than in men before the age of 50, but increased to activity values similar to those in males after that age. There were highly significant correlations with variables associated with the metabolic syndrome: plasma triglyceride, HDL- and LDL-cholesterol, apolipoprotein B and E, urate, and insulin concentrations; gamma-glutamyltransferase and aspartate and alanine aminotransferase activities; body mass index; and blood pressure. The heritability of plasma cholinesterase activity was 65%. Linkage analysis with data from the dizygotic twin pairs showed suggestive linkage on chromosome 3 at the location of the cholinesterase (BCHE) gene and also on chromosome 5.

CONCLUSIONS

Our results confirm and extend the connection between cholinesterase, cardiovascular risk factors, and metabolic syndrome. They establish a substantial heritability for plasma cholinesterase activity that might be attributable to variation near the structural gene and at an independent locus.

Non-invasive evaluation of endothelial dysfunction in uncomplicated obesity: relationship with insulin resistance

Obesity is associated with increased cardiovascular morbidity and amortality. Endothelial dysfunction, involved in the pathogenesis of cardiovascular events, has been demonstrated in obese patients with invasive techniques requiring artery catheterization. The aim of our investigation was to evaluate, with a non-invasive method readily employable on clinical grounds, impaired vasodilatation and its relationship with insulin resistance in uncomplicated obesity. 15 uncomplicated obese subjects (BMI = 36.6 +/- 3.2) and 10 lean controls (BMI = 22.9 +/- 1.25) were enrolled in this study. All subjects underwent measurement of endothelium-dependent (FBFr) vasodilatation by forearm venous occlusion pletysmography after increasing times of ischemia, and measurement of insulin sensitivity by the euglycemic hyperinsulinemic clamp technique (M index), by fasting glucose and insulin (HOMA-IR) and by oral glucose tolerance test (ISI index). Endothelium-independent (N-FBFr) vasodilatation was assessed as well. The FBFr was markedly blunted in obese patients versus lean controls (30 s: 2.12 +/- 0.34 vs. 3.63 +/- 0.22, P < 0.01; 60 s: 2.34 +/- 0.42 vs. 3.82 +/- 0.53, P < 0.01; 180 s: 3.20 +/- 0.45 vs. 7.15 +/- 0.35, P < 0.01; 300 s: 4.08 +/- 0.94 vs. 14.1 +/- 0.82, P < 0.001). The N-FBFr was not different in the two groups. High correlation was found between M index and FBFr at all ischemia times. HOMA-IR and ISI were not related with FBFr. The non-invasive evaluation of endothelial dysfunction by a simple and reliable method based on venous occlusive plethysmography shows high correlation between impaired endothelium-dependent vasodilatation and insulin resistance in uncomplicated obesity. This non-invasive test of endothelial function may be routinely performed in the assessment of cardiovascular risk in uncomplicated obesity.

Coronary and peripheral blood flow changes following biventricular pacing and their relation to heart failure improvement

AIMS

To study the effect of cardiac resynchronization therapy (CRT) on coronary and peripheral arterial circulation and to assess whether their changes are related to the improvement in patients' functional capacity and prognostically important biochemical markers.

METHODS AND RESULTS

Twenty-five patients were studied (New York Heart Association classes III and IV, left ventricular ejection fraction <35%, QRS>120 ms, mean age 66 +/- 2.1 years). Coronary blood flow (CBF), forearm blood flow (FBF), and their reserve were measured by transoesophageal echocardiography (in cm/s) and venous occlusion plethysmography (in mL/100 mL/min) at baseline and following 3 months of CRT. N-terminal-pro-brain natriuretic peptide (Nt-pro-BNP) and serum adhesion molecules, sICAM-1 and sVCAM-1 levels were also assessed. CRT induced a non-significant increase in resting CBF (baseline vs. CRT: 52.1 +/- 5.5 vs. 58.2 +/- 3.6, P: NS), whereas hyperaemic CBF was increased by CRT (baseline vs. CRT: 67.8 +/- 6.8 vs. 79.8 +/- 6.2, P < 0.05). Significant increases were observed in resting FBF (baseline vs. CRT: 1.6 +/- 0.2 vs. 2.6 +/- 0.2, P < 0.05) and hyperaemic FBF (baseline vs. CRT: 2.1 +/- 0.2 vs. 3.2 +/- 0.3, P < 0.05). The per cent difference in hyperaemic FBF was related to the per cent change in Nt-pro-BNP (r = -0.71, P < 0.05) and the per cent improvement in exercise duration (r = 0.80, P < 0.05).

CONCLUSION

CRT induces favourable changes in coronary and peripheral arterial function. Changes in peripheral blood flow are related to patients' improvement and may be prognostically significant.

Scintigraphic Imaging of Endothelium-Dependent Vasodilation in the Forearm A Preliminary Report

BACKGROUND

The diagnosis of endothelial dysfunction has been gaining clinical importance, but although endothelial function testing is available in the research setting, no technique yet exists that is simple, safe, reproducible and easily performed as a clinical screening method. The aim of this study was to design a new, scintigraphic method of imaging the flow-mediated dilation in the forearm, which represents the functional characteristic of endothelial dysfunction.

METHODS AND RESULTS

The study group comprised 118 subjects in whom left forearm ischemia was induced by inflating a sphygmomanometer cuff to supra systolic pressure for 4.5 min. Later, dynamic acquisition (2 s frame/min) was initiated after the injection of technetium-99m methoxy-isobutyl isonitril into the dorsal pedal veins. Equivalent regions of interest were drawn on both arms to detect total activity counts during 1 min and the perfusion ratios (left arm/right arm) were calculated. The left arm counts (22,203.3+/-12,372.7) were significantly higher than the right arm counts (9,980.9+/-5,931.9) (p<0.001). A significant decrease in perfusion ratios was noted in the hypertension and hypercholesterolemia groups. An increase in the number of risk factors caused an insignificant decrease in perfusion ratio (p=0.346).

CONCLUSION

Non-invasive evaluation of endothelium-dependent vasodilation by semiquantitative scintigraphic method using radioactive perfusion tracer provided promising results.

Insulin resistance causes impaired vasodilation and hypofibrinolysis in young women with polycystic ovary syndrome

INTRODUCTION

Insulin resistance, a novel cardiovascular risk factor, is often associated with increased plasminogen activator inhibitor-1 levels and impaired vasodilation. Insulin infusion in the forearm induces plasminogen activator inhibitor-1 and tissue plasminogen activator expression and endothelium-dependent vasodilation in normal subjects. The present study explores the relationship between insulin-induced vasodilatory and fibrinolytic properties of the endothelium in women with polycystic ovary syndrome, frequently affected by insulin resistance and early atherosclerosis.

MATERIALS AND METHODS

Metabolic, hormonal and fibrinolytic parameters were evaluated in 64 patients with polycystic ovary syndrome (19 insulin-resistant and 45 insulin-sensitive) and in 25 controls. In 16 women with polycystic ovary syndrome, 8 insulin-resistant and 8 insulin-sensitive, blood flow, plasminogen activator inhibitor-1 and tissue plasminogen activator expression were evaluated during insulin infusion into the forearm.

RESULTS

Elevated basal plasminogen activator inhibitor-1 levels were found in women with polycystic ovary syndrome, correlating directly with insulin levels. Plasminogen activator inhibitor-1 expression increased during insulin infusion in all women with polycystic ovary syndrome, but was delayed and sustained in insulin-resistant patients (p<0.01). Vasodilatory response to insulin was blunted (p<0.01) and tissue plasminogen activator expression abolished in insulin-resistant patients (p<0.01).

CONCLUSION

Our study demonstrates that women with polycystic ovary syndrome and insulin resistance show a blunted endothelial-dependent vasodilation. The impaired endothelial release of tissue-plasminogen activator and the sustained plasminogen activator inhibitor-1 release during insulin infusion suggest a hypofibrinolytic state in PCOS patients with insulin resistance. This hemodynamic and fibrinolytic derangement may contribute to the pathogenesis of early atherosclerosis in insulin resistance.