Polymorphisms in the renin–angiotensin system and endothelium‐dependent vasodilation in normotensive subjects

Background Our aim was to test the hypothesis that genes encoding components in the renin–angiotensin system influence endothelial vasodilatory function. Methods In 59 apparently healthy, normotensive individuals, endothelium‐dependent vasodilation (EDV) and endothelial‐independent vasodilation (EIDV) was evaluated by infusing metacholine and sodium nitroprusside into the brachial artery. Forearm blood flow was measured by venous occlusion plethysmography. The ACE insertion (I)/deletion (D) polymorphism, the T174M and M235T angiotensinogen restriction fragments length polymorphisms, the angiotensin II receptor type 1 (AT1R) A1166C, and the aldosterone synthase gene (CYP11B2) C‐344T polymorphisms were analysed. Results When analysing the ACE, the two angiotensinogen and the aldosterone synthase CYP11B2 genotypes independently, no significant association with endothelial vasodilatory function was found. However, a significant reduction in endothelium‐dependent vasodilation was observed in the subjects (n=9) with the ACE D allele and the angiotensinogen T174M genotype (P<0·05). Subjects with the AT1R genotype AC showed a reduction in both EDV (P=0·05) and EIDV (P=0·04) when compared with those with the AA genotype. Conclusions The subjects with the ACE D allele in combination with the angiotensinogen T174M genotype are associated with a reduced EDV. This together with the observation that the AC AT1R genotype is associated with a reduction in both EDV and EIDV, supports the hypothesis that endothelial vasodilatory function is influenced by genes in the renin–angiotensinogen system.     

Atherosclerosis measured by whole body magnetic resonance angiography and carotid artery ultrasound is related to arterial compliance,but not to endothelium‐dependent vasodilation – the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study

Background: Arterial compliance and endothelium‐dependent vasodilation are two characteristics of the vessel wall. In the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study, we studied the relationships between arterial compliance and endothelium‐dependent vasodilation versus atherosclerosis as measured with two imaging modalities. Methods: In the population‐based PIVUS study (1016 subjects aged 70), arterial compliance was determined by ultrasound in the carotid artery and the stroke volume to pulse pressure ratio by echocardiography, while endothelium‐dependent vasodilation was assessed by the invasive forearm technique with acetylcholine and brachial artery ultrasound. Intima‐media thickness was evaluated by ultrasound in the carotid artery (n = 954). Stenosis in the carotid, aorta, renal, upper and lower leg arteries were determined by magnetic resonance angiography in a random subsample of 306 subjects. Results: After adjustments for gender, Framingham risk score, obesity, myocardial infarction and stroke, distensibility in the carotid artery and the stroke volume to pulse pressure ratio were both significantly related to a weighted index of stenosis in the five arterial territories evaluated by magnetic resonance angiography (p<0·02 for both). Distensibility in the carotid artery (P = 0·021), but not the stroke volume to pulse pressure ratio (P = 0·08), was also significantly related to intima‐media thickness. Conclusion: In the elderly population, atherosclerosis is mainly related to arterial compliance, but not to endothelium‐dependent vasodilation in peripheral conduit or resistance vessels.     

彩色多普勒超声评价肱动脉直径和血流介导的扩张反应与冠心病的关系

目的 采用彩色多普勒超声评价肱动脉直径和血流介导的扩张反应(FMD)与冠心病的关系。方法 随机入选因胸痛住院并行冠状动脉造影检查的患者45例，在冠状动脉造影前进行肱动脉超声检查，分别测量肱动脉直径和加压充血后肱动脉直径的变化，通过冠状动脉造影确定冠心病组患者22例，非冠心病组患者23例，分别比较结果。结果 冠心病组较非冠心病组休息时肱动脉直径差异有统计学意义，而FMD则差异无统计学意义。结论 利用超声测量肱动脉直径可以作为一种无创性诊断冠心病的方法。     

Chronic treatment with taurine ameliorates diabetes‐induced dysfunction of nitric oxide‐mediated neurogenic and endothelium‐dependent corpus cavernosum relaxation in rats

This study was aimed to examine the effect of chronic taurine treatment on corpus cavernosum dysfunction in diabetic rats and to investigate possible underlying mechanisms. Thirty male rats were randomized to three groups of 10 each, including control, diabetic, and taurine‐treated diabetic. Diabetes was induced in rats by streptozotocin (STZ, single intraperitoneal dose of 50 mg/kg body weight). Taurine was administered orally for 12 weeks (1% w/v in drinking water) from the day on which STZ was injected. At the end of the 12th week, strips of corpus cavernosum were suspended in an organ bath system for functional studies. Nitric oxide (NO)‐mediated endothelium‐dependent and neurogenic corpus cavernosum relaxation were evaluated by acetylcholine (ACh, 0.1–100 μm ) and electrical field stimulation (EFS, 30 V, 5 ms, 2–32 Hz), respectively. The expressions of endothelial nitric oxide synthase (eNOS), phosphorylated eNOS (p‐eNOS) (Ser‐1177), neuronal nitric oxide synthase (nNOS), NADPH oxidase subunit gp91^phox, Rho A, and Rho kinase in corpus cavernosum were semi‐quantitatively assessed by immunohistochemistry. Induction of diabetes resulted in significant inhibition of NO‐mediated endothelium‐dependent and neurogenic corpus cavernosum relaxation. Furthermore, eNOS, p‐eNOS, and nNOS expressions decreased significantly in diabetic rats compared to controls, while gp91^phox, RhoA and Rho kinase expressions increased significantly. The diminished relaxation response to ACh and EFS as well as diabetes‐related changes in expressions of these proteins in corpus cavernosum of diabetic rats was significantly improved by taurine. Taurine treatment improves NO‐mediated relaxations of corpus cavernosum in diabetic rats probably by inhibiting NADPH oxidase/Rho kinase pathways.     

Molecular control of blood flow and angiogenesis: role of nitric oxide

Summary.  In the past decade, the importance of the vascular endothelium as a multifunctional regulator of vascular smooth muscle physiology and pathophysiology has been appreciated . Indeed, the endothelium responds to hemodynamic stimuli (pressure, shear stress and wall strain) and locally manufactured mediators (such as bradykinin, prostaglandins, angiotensin II and nitric oxide) that can influence blood flow, cell trafficking into tissue and angiogenesis. In this chapter, the importance of nitric oxide (NO) as a mediator of blood flow control, vascular permeability and angiogenesis will be discussed.     

Methodological aspects of the evaluation of endothelium-dependent vasodilatation in the human forearm

The present study, involving 56 healthy subjects from a health screening, was undertaken to address some methodological questions regarding the measurement of endothelial function using local intra-arterial infusions of metacholine (2 and 5 μg min^?1) to evaluate endothelium-dependent vasodilatation, and sodium nitroprusside (SNP, 5 and 10 μg min^?1) to evaluate endothelium-independent vasodilatation. Forearm blood flow (FBF) was measured by venous occlusion plethysmography. The ratio of FBF during the highest dose of metacholine to FBF during the highest dose of SNP was used as an index of endothelial function. In 10 young volunteers the procedure was repeated after 2 h and again after 3 weeks in order to study short-term and long-term reproducibility of the method. Neither the vasodilatatory response to metacholine (r = 0·006) nor that to SNP (r = 0·08) was related to resting FBF. Neither the circumference nor the length of the arm was related to endothelial function (r = 0·01?0·11), as evaluated by the FBF on metacholine to nitroprusside ratio (mean 1·3 ± 0·3 SD). The use of a wrist cuff to exclude hand circulation, or not, did not influence the evaluation of endothelial function significantly. Maximal FBF after 3 min of arterial occlusion of the forearm was significantly related to blood flow during both metacholine (r = 0·53, P < 0·01) and nitroprusside infusion (r = 0·36, P < 0·05), but not to the FBF on metacholine to nitroprusside ratio (r = 0·01). The short-term and long-term reproducibility of FBF during vasodilatation with metacholine and SNP was good (r = 0·89?0·97, P < 0·001), while the individual measurements for resting FBF were less reproducible when repeated after 3 weeks (r = 0·34). In conclusion, endothelial function was not related to resting FBF, nor to the arm circumference or length. No major difference was seen whether endothelial function was evaluated with or without exclusion of the hand circulation. Maximal FBF during reactive hyperaemia was not related to endothelial function.     

Alterations in the peripheral circulation in COPD patients

RATIONALE: Although various factors influence peripheral circulation in chronic obstructive pulmonary disease (COPD) patients, little is known about the vasomotor changes in these subjects. OBJECTIVES: The present study was designed to assess alterations in the brachial circulation of COPD patients. METHODS: Twenty-five COPD patients and 25 healthy subjects were studied. Brachial artery (BA) blood flow and indices of BA stiffness were investigated by two-dimensional ultrasonography and pulsed Doppler. Cardiac dimensions, left ventricular (LV) function and cardiac output were assessed by pulsed Doppler echocardiography. MAIN RESULTS: A significant increase in LV mass was observed in the COPD group despite normal arterial pressure. Total arterial compliance and BA compliance were significantly decreased in COPD patients in comparison with healthy subjects. Heart rate was increased in COPD patients and was inversely correlated with PaO(2) and forced expiratory volume in the first second (FEV(1)). A decrease in LV preload was expressed by a reduction in LV diastolic diameters and LV stroke volume. Patients with severe COPD have a lower BA surface area than patients with moderate COPD. FEV(1) and PaO(2) were significantly related to BA compliance. CONCLUSION: In COPD patients, significant alterations in the peripheral circulation were observed. Moreover, the magnitude of changes in the peripheral circulation was related to the severity of COPD.     

Impaired coronary artery distensibility is an endothelium‐dependent process and is associated with vulnerable plaque composition

Coronary endothelial‐dependent microvascular dysfunction, an early reversible stage of coronary artery disease (CAD), is associated with poor clinical outcome. The current study investigated whether coronary artery distensibility index (CDI) is associated with: (i) coronary endothelial‐dependent microvascular dysfunction and (ii) vulnerable plaque composition among subjects with non‐obstructive CAD. Seventy‐four subjects with non‐obstructive CAD (luminal stenosis <30%) were studied. In 20 subjects with and without coronary endothelial‐dependent microvascular dysfunction, coronary flow reserve (CFR) of target segment during intracoronary (IC) infusion of acetylcholine (Ach) and bolus injection of adenosine as well as CDI at rest of corresponding target segment were measured. In 54 subjects, plaque compositions and CDI at rest of 154 non‐obstructive coronary segments as well as proximal segment without disease were measured by intravascular ultrasound (IVUS). CDI was defined as: [(Early‐diastolic cross‐sectional‐area (CSA) – End‐diastolic CSA of target segment)/(end‐diastolic CSA of target segment × coronary‐pulse‐pressure) × 10³]. There is a direct association between endothelial dysfunction and impaired CDI of a coronary segment both in the given coronary segment and corresponding microvessels in which a strong agreement between CDI and CFR Ach (r² = 0·85, P = 0·0001) was observed. Multivariable regression‐analysis showed that CDI was an independent predictor of the vulnerable plaque characteristics. The risk of impaired CDI was 125% higher in segments with necrotic core and 60% higher in segments with fibrofatty components as compared to normal segments (P = 0·001). In conclusions, the current study reveals that impaired CDI is an endothelial‐dependent process of both given coronary segment and corresponding microvessels and is associated with vulnerable plaque composition.     

Oral folate enhances endothelial function in hyperhomocysteinaemic subjects

BACKGROUND: Elevated plasma homocysteine (Hcy) is a risk factor for vascular disease. A postulated mechanism is vascular endothelial damage by homocysteine. Hcy levels are inversely related to blood concentrations of folate and can be lowered by folate supplements. The effect of oral folic acid on endothelial function was investigated in healthy adults with mild hyperhomocysteinaemia. PATIENTS AND METHODS: Eighteen healthy subjects (Hcy > 13 micromol L-1 at entry), from a screening population of 890 volunteers, were entered into a randomised double-blind placebo-controlled crossover study of oral folic acid (5 mg daily for six weeks) with a six week interval between treatments. Flow-mediated (endothelium-dependent) and (endothelial-independent) glyceryl trinitrate (GTN)-mediated brachial artery dilatation were measured by high resolution wall tracking. RESULTS: Folate supplementation enhanced endothelium-dependent responses (+0.08 +/- 0.05 vs. +0.04 +/- 0.04 mm, P = 0.015) but endothelium-independent responses (GTN) were unchanged. Folate reduced Hcy (8.7 +/- 2.5 vs. 12.1 +/- 3.6 micromol L-1). CONCLUSION: High dose folic acid supplementation enhances endothelium-dependent vascular function and lowers plasma Hcy. This provides preliminary evidence that folate may have beneficial cardiovascular effects in adults with mild hyperhomocysteinaemia.     

Analysis of endothelium-dependent vasodilation by use of the radial artery pulse wave obtained by applanation tonometry

Objectives: To evaluate applanation tonometry as a method to obtain arterial pulse waves suitable for pulse wave analysis of the height of the diastolic inflection point (IP), and to use this technique to study endothelium‐mediated vasodilation by evaluation of the contribution of nitric oxide (NO) to the reduction in the height of the IP induced by β2‐adrenergic stimulation. Methods: The radial artery pulse waveform was recorded by applanation tonometry in young healthy subjects before and after interventions both locally in the forearm and systemically by different vasodilators and vasoconstrictors, and vasodilatation was analysed as a change in the height of the IP. The mechanism behind the reduction in the height of the IP induced by terbutaline was investigated by systemic interventions with both N(G)‐monomethyl‐l ‐arginine (l ‐NMMA) and noradrenaline (NA). Results: Applanation tonometry was a convenient method to obtain radial artery pulse waves of good quality. The reduction in IP was substantially more pronounced when vasodilators were given systemically than when given locally in the forearm, indicating that the effect was obtained through an effect on peripheral pulse wave reflection. Systemically given l ‐NMMA, but not NA, increased the IP (P<0·05). Systemically given l ‐NMMA also caused a more pronounced attenuation than NA of the reduction in IP following terbutaline injection (P<0·05). Conclusion: Changes in IP following β2‐adrenergic stimulation appears to be a measurement of pulse wave reflection mainly governed by NO. Applanation tonometry and pulse wave analysis is a minimally invasive method suitable to assess endothelium‐dependent vasodilation in large‐scale studies.     

游泳训练对糖尿病大鼠主动脉血管内皮依赖性舒张功能的改善及机制

摘要 目的:观察游泳训练对糖尿病大鼠血管内皮依赖性舒张功能的影响及其可能机制。 方法:40只健康雄性SD大鼠随机分为正常对照组（CG）,糖尿病对照组（DCG）,糖尿病游泳组（DSG）。游泳训练8周后, 取胸主动脉,离体灌流法检测其对乙酰胆碱(ACh)诱导的内皮依赖性舒张反应,及其对硝普钠(SNP)诱导的非内皮依赖性舒张反应。并测定血清一氧化氮（NO）浓度及血清葡萄糖、胰岛素、总胆固醇、甘油三酯、氧化应激状态（超氧化物歧化酶,谷胱甘肽过氧化物酶,丙二醛）。 结果:糖尿病组大鼠胸主动脉对ACh诱导的舒张反应明显减弱（P<0.05）;游泳运动能明显改善糖尿病胸主动脉内皮依赖性舒张反应;各组对SNP诱导的非内皮依赖性舒张反应无显著差异。糖尿病组的NO浓度低于正常组（P<0.05）,游泳运动显著提高了糖尿病大鼠的NO浓度。与糖尿病组相比,糖尿病游泳组大鼠血糖、胰岛素敏感性、脂质代谢改善,同时氧化应激状态显著降低。 结论:游泳运动能明显改善糖尿病大鼠胸主动脉对ACh诱导的内皮依赖性舒张反应,其机制可能是通过降低血糖,降低氧化应激,增加NO的生物活性来实现的。     

Evaluation of four different methods to measure endothelium-dependent vasodilation in the human peripheral circulation

At present, several techniques exist that claim to evaluate endothelium-dependent vasodilation (EDV) in the human peripheral circulation. The present study aims to evaluate the relationships between four of these techniques. A group of 24 young, healthy subjects underwent measurements of EDV and endothelium-independent vasodilation (EIDV) in predominately resistance vessels in the forearm using the invasive forearm technique with local infusion of methacholine and sodium nitroprusside, evaluation of flow-mediated vasodilation (FMD) in the conduit brachial artery measured by ultrasound, with or without the addition of ischaemic hand exercise, and evaluation of the reduction in the relative height of the inflection point of the radial pulse wave following beta(2)-adrenergic receptor stimulation. The reduction in the relative height of the inflection point following beta(2)-adrenergic receptor stimulation was significantly related to both EDV and EIDV in the forearm (r=-0.41 and r=-0.42 respectively; both P<0.05), but not to the EDV/EIDV ratio (r=-0.10). However, FMD, with or without the addition of ischaemic hand exercise, was not significantly related to the results obtained using the other two techniques (r=-0.18 to +0.13). In conclusion, the reduction in the relative height of the inflection point of the pulse wave following beta(2)-adrenergic receptor stimulation was related to both EDV and EIDV measured by the invasive forearm technique, indicating that the pulse wave technique does not measure EDV specifically. FMD in the brachial artery, with or without ischaemic hand exercise, was not significantly related to values obtained using the other two techniques, indicating that endothelial function differs between conduit and resistance arteries, and that both of these measurements should be evaluated in future studies.     

Low‐intensity ultrasound increases endothelial cell nitric oxide synthase activity and nitric oxide synthesis

Summary. Low‐intensity ultrasound (US) increases tissue perfusion in ischemic muscle through a nitric oxide (NO)‐dependent mechanism. We have developed a model to expose endothelial cells to well‐characterized acoustic fields in vitro and investigate the physical and biological mechanisms involved. Human umbilical vein endothelial cells (HUVEC) or bovine aortic endothelial cells (BAEC) were grown in tissue culture plates suspended in a temperature‐controlled water bath and exposed to US. Exposure to 27 kHz continuous wave US at 0.25 W cm^?2 for 10 min increased HUVEC media NO by 102 ± 19% (P < 0.05) and BAEC by 117 ± 23% (P < 0.01). Endothelial cell NO synthase activity increased by 27 ± 24% in HUVEC and by 32 ± 16% in BAEC (P < 0.05 for each). The cell response was rapid with a significant increase in NO synthesis by 10 s and a maximum increase after exposure for 1 min. By 30 min post‐exposure NO synthesis declined to baseline, indicating that the response was transient. Unexpectedly, pulsing at a 10% duty cycle resulted in a 46% increase in NO synthesis over the response seen with continuous wave US, resulting in an increase of 147 ± 18%. Cells responded to very low intensity US, with a significant increase at 0.075 W cm^?2 (P < 0.01) and a maximum response at 0.125 W cm^?2. US caused minor reversible changes in cell morphology but did not alter proliferative capacity, indicating absence of injury. We conclude that exposure of endothelial cells to low‐intensity, low‐frequency US increases NO synthase activity and NO production, which could be used to induce vasodilatation experimentally or therapeutically.     

Real‐time ultrasound measurements of changes in suboccipital vertebral artery diameter and blood flow velocity associated with cervical spine rotation

Background and Purpose . The vulnerability of the vertebral artery (VA) to distortion with sustained, full‐range cervical spine rotation, resulting in compromised blood flow and possible vertebrobasilar ischaemia, is well recognized. However, few studies have measured such blood flow changes in the parts of the VA downstream from the region of maximum cervical spine rotation: the suboccipital (VA3) and intracranial vertebral arteries. The purpose of this experimental study was to visualize the VA3 and record the changes in its blood flow associated with cervical spine rotation. Method . VA3 diameters and blood flow velocities were measured in the neutral cervical spine position and with active full‐range rotation to the left and right, in 35 healthy female subjects, using colour‐coded real‐time ultrasound. Results . Both left and right VA3 diameters and blood flow velocities decreased significantly on ipsilateral rotation. These values increased non‐significantly in the left VA3 and decreased non‐significantly in the right VA3 on contralateral rotation. Conclusions . The results of this study suggest that the distortion or compression of VA3 demonstrated by the reduction in diameter on ipsilateral cervical spine rotation, particularly, was sufficient to result in compromised blood flow. A significant stretching effect of VA3, on contralateral rotation, was not demonstrated in these subjects. Nevertheless, these findings add evidence to support the recommendation that sustained, full‐range cervical spine rotation should be avoided in professional practice. Copyright © 2008 John Wiley & Sons, Ltd.     

Hyperaemic blood-flow velocities in systole and diastole relate to coronary risk in divergent ways

BACKGROUND: A recent study suggested blood-flow velocity in diastole during reactive hyperaemia as a major driver of flow-mediated vasodilation (FMD) of the brachial artery, also being related to cardiovascular risk factors. The present study aimed to investigate the relative importance of hyperaemic systolic and diastolic blood-flow velocity in the forearm regarding both FMD and cardiovascular risk factors. METHODS: In the Prospective Investigation of the Vasculature in Uppsala Seniors study, conducted in 1016 subjects aged 70 years, FMD, systolic and diastolic blood hyperaemic flow velocities in the brachial artery were evaluated by ultrasound. RESULTS: Hyperaemic blood-flow velocity both in systole and diastole were related to FMD (r = 0.14-0.19, P<0.0001). However, while hyperaemic systolic blood-flow velocity was related to coronary risk (Framingham risk score) in a positive way (r = 0.08, P = 0.013), diastolic blood-flow velocity was inversely related to coronary risk (r = -0.08, P = 0.016). Therefore, the systolic to diastolic hyperaemic blood-flow velocity ratio was more powerful related to coronary risk (r = 0.23, P = 0.0001). In a multiple regression model, both FMD and the systolic to diastolic hyperaemic blood-flow velocity ratio were independent predictors of coronary risk (P = 0.018 and P = 0.0001). CONCLUSION: As hyperaemic blood-flow velocities in systole and diastole in the brachial artery were related to coronary risk in divergent ways, the ratio thereof is a promising index of vascular function providing independent information regarding coronary risk when compared with FMD.     

Whole‐body vibration dosage alters leg blood flow

The effect of whole‐body vibration dosage on leg blood flow was investigated. Nine healthy young adult males completed a set of 14 random vibration and non‐vibration exercise bouts whilst squatting on a Galileo 900 plate. Six vibration frequencies ranging from 5 to 30 Hz (5 Hz increments) were used in combination with a 2·5 mm and 4·5 mm amplitude to produce twelve 1‐min vibration bouts. Subjects also completed two 1‐min bouts where no vibration was applied. Systolic and diastolic diameters of the common femoral artery and blood cell velocity were measured by an echo Doppler ultrasound in a standing or rest condition prior to the bouts and during and after each bout. Repeated measures MANOVAs were used in the statistical analysis. Compared with the standing condition, the exercise bouts produced a four‐fold increase in mean blood cell velocity (P<0·001) and a two‐fold increase in peak blood cell velocity (P<0·001). Compared to the non‐vibration bouts, frequencies of 10–30 Hz increased mean blood cell velocity by approximately 33% (P<0·01) whereas 20–30 Hz increased peak blood cell velocity by approximately 27% (P<0·01). Amplitude was additive to frequency but only achieved significance at 30 Hz (P<0·05). Compared with the standing condition, squatting alone produced significant increases in mean and peak blood cell velocity (P<0·001). The results show leg blood flow increased during the squat or non‐vibration bouts and systematically increased with frequency in the vibration bouts.