Endothelium-derived nitric oxide regulates arterial elasticity in human arteries in vivo

Catheter-based intraluminal sonography

With the development of interventional and minimally invasive surgical techniques in the last decade, a strong interest in intraluminal sonography has arisen because of the need for better imaging information and management of the interventional procedure. High-resolution intraluminal sonography is a unique approach for the evaluation of a wide range of abnormalities within the luminal structures throughout the body. This imaging technique has been able to obtain information not available with even the most sophisticated percutaneous sonography, CT, or MRI. The uniqueness of this approach has led to extensive research, establishing a variety of clinical applications. These miniature catheter-based transducers have become important supplemental tools in the evaluation of the urinary and gastrointestinal tracts. Other areas need to be evaluated more thoroughly before efficacy is established, but the concept of using miniature transducers has shown promise in many areas of the body. This should lead to the provision of important information for decision making relative to patient care and surgical intervention. In the future, with projected technical progress, intraluminal sonography should substantially improve its diagnostic capabilities.

Endothelin-1 regulates arterial pulse wave velocity in vivo

OBJECTIVES

The aim of this study was to investigate whether endothelin-1, acting locally, regulates arterial distensibility, assessed by measuring pulse-wave velocity in vivo.

BACKGROUND

Arterial stiffness is a key determinant of cardiovascular risk. Several lines of evidence support a role for the endothelium in regulating arterial stiffness by release of vasoactive mediators. However, the role of endothelin-1 (ET-1) in the regulation of arterial stiffness has not been investigated.

METHODS

All studies were conducted in anesthetized sheep. Pulse wave velocity (PWV) was calculated using the foot-to-foot methodology from two pressure waveforms simultaneously recorded with a high-fidelity, dual pressure-sensing catheter placed in the common iliac artery.

RESULTS

Intra-arterial infusion of ET-1 significantly increased iliac PWV by 12 +/- 5% (mean +/- STD; p < 0.001), whereas infusion of the endothelin-A (ET(A)) receptor antagonist BQ-123 significantly reduced PWV by 12 +/- 4% (p < 0.001). After BQ-123 infusion, exogenously infused ET-1 did not significantly change PWV compared with infusion of saline (change of -0.08 +/- 0.11% vs. -0.01 +/- 0.07%; p = 0.53). Importantly, infusion of BQ-123 or ET-1 distal to the common iliac artery did not affect PWV.

CONCLUSIONS

These results demonstrate, for the first time, that endogenous ET-1 production directly regulates large artery PWV in vivo. In addition, exogenous ET-1 increases PWV, and this can be blunted by ET(A) receptor blockade. These observations explain, in part, why conditions that exhibit up-regulation of ET-1 are also associated with arterial stiffening. Therefore, drugs that block ET(A) receptors may be effective in reducing large artery stiffness in humans, and thus cardiovascular risk.

The Role of Exercise in the Treatment of Cardiovascular Disease Associated with Type 2 Diabetes Mellitus

The role of exercise training in the prevention and treatment of type 2 diabetes mellitus has been studied extensively over the past two decades. Although the primary treatment aim for patients with type 2 diabetes is metabolic control, the morbidity and mortality associated with the disease is more a function of cardiovascular disease. As exercise is associated with favourable reductions in the risk for cardiovascular disease in other high-risk populations, here we explore the role of exercise in the treatment of cardiovascular maladaptations associated with type 2 diabetes. The cardiovascular adaptation to type 2 diabetes is characterised by hypertrophy, stiffening and loss of functional reserve. Clinically, the cardiovascular adaptations to the diabetic state are associated with an increased risk for cardiovascular disease. Functionally, these adaptations have been shown to contribute to a reduced exercise capacity, which may explain the reduced cardiovascular fitness observed in this population. Exercise training is associated with improved exercise capacity in various populations, including type 2 diabetes. Several structural and functional adaptations within the cardiovascular system following exercise training could explain these findings, such as reductions in ventricular and vascular structural hypertrophy and compliance coupled with increased functional reserve. Although these cardiovascular adaptations to aerobic exercise training have been well documented in older populations with similar decrements in cardiovascular fitness and function, they have yet to be examined in patients with type 2 diabetes. For this reason, we contend that exercise training may be an excellent therapeutic adjunct in the treatment of diabetic cardiovascular disease.

Comparison of in vivo effects of nitroglycerin and insulin on the aortic pressure waveform

BACKGROUND

Individuals whose platelets are resistant to the antiaggregatory effects of insulin in vitro are also resistant to the antiaggregatory effects of nitroglycerin (GTN). We have previously shown that insulin acutely diminishes central wave reflection in large arteries and that this action of insulin is blunted in insulin-resistant subjects. However, as yet, no studies have compared the haemodynamic effects of insulin and GTN on large arterial function in the same group of subjects. The aim of this study was to determine whether resistance to the haemodynamic effects of insulin is a defect specific to insulin or whether individuals resistant to the vascular actions of insulin are also resistant to GTN.

DESIGN AND RESULTS

Dose-response characteristics of insulin and GTN on the aortic waveform were determined using applanation tonometry and pulse wave analysis (PWA) in seven healthy men (age 26 +/- 1 year, BMI 25 +/- 2 kg m(-2)). Three doses of sublingual GTN (500 microg for 1, 3 or 5 min) and insulin (0.5, 1 or 2 mU kg(-1) min(-1) for 120 min) were administered on three separate occasions. Both agents dose-dependently decreased central pulse pressure and the augmentation index (AIx) without changing brachial artery blood pressure. We next compared responses to insulin (2 mU kg(-1) min(-1) for 120 min) and sublingual GTN (500 microg for 5 min) in 20 nondiabetic subjects (age 50 +/- 2 year, BMI 21.0-36.3 kg m(-2)). Again, both agents significantly decreased AIx. Although the vascular effects of insulin and GTN vascular were positively correlated [Spearman's r=0.92 (95% confidence interval 0.81-0.97), P<0.0001], the time-course for the action GTN was faster than that of insulin. Brachial systolic blood pressure remained unchanged during the insulin infusion (122 +/- 3 vs. 121 +/- 3 mmHg, 0 vs. 120 min) but aortic systolic blood pressure decreased significantly by 30 min (111 +/- 3 vs. 107 +/- 3 mmHg, 0 vs. 30 min, P<0.01). Similarly, GTN decreased aortic systolic blood pressure from 119 +/- 4 to maximally 112 +/- 3 mmHg (P<0.001) without significantly decreasing systolic blood pressure in the brachial artery.

CONCLUSIONS

The effects of insulin and GTN on large arterial haemodynamics are dose-dependent and significantly correlated. The exact mechanisms and sites of action of insulin and GTN in subjects with insulin resistance remain to be established.

Vascular elasticity from regional displacement estimates

A recently-developed ultrasonic technique for measuring elastic properties of vascular tissue is evaluated using computer simulations, phantom and in vivo human measurements. A time sequence of displacement images is measured over the cardiac cycle to describe the spatial and temporal patterns of deformation surrounding arteries. This information is combined with a mathematical model to estimate an elastic modulus. Computer simulations of ultrasonic echo data from deformed tissues are analyzed to define a signal processing approach. Measurements in flow phantoms, with and without vessel-simulating channel walls, provide an assessment of the accuracy and precision of this technique for vascular elasticity measurements. Finally, preliminary results for the stiffness index (beta) in a study group of healthy human volunteers are compared with previously reported data. We find that careful measurement technique is required to control measurement variability.

Characteristics of 24 h telemetered blood pressure in eNOS-knockout and C57Bl/6J control mice

The purpose of the present study was to characterize in detail the 24 h blood pressure (BP) phenotype of mice lacking the gene for endothelial nitric oxide synthase (eNOS-/-) and the corresponding control strain (C57Bl/6J). Twenty-four hour BP recordings were made in conscious 12- to 16-week-old male mice 10 days following the implantation of a BP telemeter (n = 9 per group). The BP and heart rate of both strains were markedly affected by brief locomotor activity cycles, resulting in bimodal distributions of BP and heart rate within both light and dark periods. Data from active periods were associated with the higher of the two modes, whereas data from inactive periods were associated with the lower of the two modes. In eNOS-/- mice, the 24 h average BP level was significantly elevated (+15 %, 104 +/- 2 vs. 119 +/- 1 mmHg), as was its daily range (+44 %), its coefficient of variation (+26 %), dark-light difference (+48 %), and the separation of the two modes of its distribution (+41 %). Pulse pressure was also significantly greater (+23 %) in eNOS-/- mice. The 24 h heart rate level did not differ between control and eNOS-/- mice. Considerable variation was noted among previously published values of BP in eNOS-/- mice, but not in the corresponding control mice. Our results indicate that eNOS-/- mice have mild hypertension that is accompanied by more pronounced increases in BP lability and/or reactivity. Our results also demonstrate a marked effect of locomotor activity on BP in mice, which may confound short-term measurements of BP.

Pulse wave analysis and pulse wave velocity: a critical review of their strengths and weaknesses

The study of the pulse using the technique of applanation tonometry is undergoing a resurgence with the development of new computerized equipment. We aim here to present a critical review of the uses, potential uses, strengths and weaknesses of the technique of applanation tonometry for the assessment of augmentation index and pulse wave velocity. We will review the technique of applanation tonometry, the physiological factors affecting pulse wave velocity and pulse wave analysis, the changes in pulse wave velocity and pulse wave analysis with pharmacological interventions, and the use of the technique of applanation tonometry as a prognostic tool. We conclude that, although the technique of applanation tonometry initially seems promising, several pertinent issues need to be addressed before it can be used reliably as a clinical or research tool. Importantly, use of the technique of applanation tonometry to derive the central waveform from non-invasively acquired peripheral data needs to be validated prospectively.

Arterial distensibility: acute changes following dynamic exercise in normal subjects

The time course of acute changes in large artery distensibility immediately and for 60 min following maximum treadmill exercise in normal subjects was characterized by simultaneously measuring upper and lower limb pulse wave velocity (PWV). A new oscillometric technique was used, which has proven to be sensitive to changes in distensibility induced by acute changes in vascular tone independently of blood pressure. The observed changes in PWV are attributable to changes in vascular tone corresponding to recovery from a systemic net constrictor response and a local net dilator response to exercise with persisting postexercise vasodilatation. They are inadequately explained by associated changes in blood pressure and cannot be attributed to changes in heart rate or viscosity. Modeled as a system of n coupled linear differential equations, the minimum (and adequate) order required to reproduce these patterns was n = 1 for the upper and n = 2 for the exercising lower limb. The economy of the solution suggests entrainment among the multiple interactive mechanisms governing vasomotor control.

Coronary and systemic hemodynamic effects of sildenafil citrate: from basic science to clinical studies in patients with cardiovascular disease

Sildenafil citrate is the first oral phosphodiesterase type 5 inhibitor approved for the treatment of erectile dysfunction. The wide use of sildenafil by patients with erectile dysfunction and cardiovascular disease has resulted in a considerable number of independent studies investigating the cardiovascular safety and functional role of the phosphodiesterase type 5-cyclic guanosine monophosphate-nitric oxide pathway in the cardiovascular system. Endothelial dysfunction, defined as a reduction in the bioavailability of nitric oxide, is associated with many of the common risk factors for cardiovascular disease and erectile dysfunction. Sildenafil has been demonstrated to improve the vasomotor aspect of endothelial dysfunction in patients with heart failure and diabetes. Hemodynamic studies suggest that sildenafil is a modest vasodilator with the potential to increase coronary blood flow and coronary flow reserve. In patients with ischemic heart disease, sildenafil is associated with reductions in mean arterial and pulmonary pressure with little effect on heart rate, cardiac output, and systemic or pulmonary vascular resistance. The absence of an effect on cardiac output supports the lack of an inotropic effect of sildenafil. This is consistent with the finding that sildenafil has no effect on cyclic adenosine monophosphate levels in the vasculature. Finally, exciting reports have emerged from clinical experience with the use of phosphodiesterase type 5 inhibitors in patients with pulmonary hypertension.

Angiotensin II and nitric oxide interaction

Nitric oxide degradation linked to endothelial dysfunction plays a central role in cardiovascular diseases. Superoxide producing enzymes such as NADPH oxidase and xanthine oxidase are responsible for NO degradation as they generate a variety of reactive oxygen species (ROS). Moreover, superoxide is rapidly degraded by superoxide dismutase to produce hydrogen peroxide leading to the uncoupling of NO synthase and production of increased amount of superoxide. Angiotensin II is an important stimulus of NADPH oxidase. Through its AT(1) receptor, Ang II stimulates the long-term increase of several membrane component of NADPH oxidase such as P(22) phox or nox-1 and causes an increased activity of NADPH oxidase with inactivation of NO leading to impaired endothelium-dependent vasorelaxation, vascular smooth muscle cell hypertrophy, proliferation and migration, extracellular matrix formation, thrombosis, cellular infiltration and inflammatory reaction. Several preclinical and clinical studies have now confirmed the involvement of the AT(1) receptor in endothelial dysfunction. It is proposed that the AT(2) receptor counterbalances the deleterious effect of the Ang II-induced AT(1) receptor stimulation through bradykinin and NOS stimulation. This mechanism could be especially relevant in pathological cases when the NADPH oxidase activity is blocked with an AT(1) receptor antagonist.