Loss Of Endothelium-dependent Vasodilation Research Articles

Activation of Endothelial Potassium Channels Lowers Pulmonary Arterial Pressure in Pulmonary Hypertension

Endothelium‐dependent vasodilation of small pulmonary arteries (PAs) lowers the resting pulmonary arterial pressure (PAP). Moreover, a loss of endothelium‐dependent vasodilation is a major contributor to elevated PAP in pulmonary hypertension (PH). Therefore, therapeutic strategies specifically targeting endothelial vasodilatory mechanisms may have beneficial effects on PAP in PH. In this regard, endothelial Ca2+ signaling mechanisms promote PA dilation and may present potential therapeutic targets for lowering PAP in PH. Under homeostatic conditions, Ca2+ signals activate endothelial nitric oxide synthase (eNOS) and Ca2+‐sensitive intermediate and small conductance potassium (IK and SK) channels to dilate PAs. eNOS activity and NO signaling are impaired in PH. However, the activity of IK/SK channels and its effect on PAP in PH have not been investigated. We hypothesized that IK/SK channels can be targeted for lowering PAP in PH. A mouse model of PH (chronic hypoxia + Sugen 5416, hereafter CH+Su, for 3 weeks) showed elevated right ventricular systolic pressure (RVSP, an indirect indicator of PAP) and development of pulmonary arterial lesions. We recently showed that adenosine triphosphate (ATP) dilates PAs through Ca2+‐dependent activation of eNOS in normal mice (Daneva et al., PNAS, 2021). PA pressure myography experiments demonstrated that ATP was unable to dilate PAs from CH+Su mice, confirming a loss of eNOS‐dependent vasodilation in these mice. However, PA dilation in response to IK/SK channel agonist NS309 (1 μM) was not different between PAs from control and CH+Su mice. Whole‐cell patch‐clamp studies in freshly isolated endothelial cells showed that IK/SK channel activity is not impaired in the endothelium from CH+Su mice. Finally, intraperitoneal administration of the IK/SK channel activator better suited for in vivo treatment, SKA‐31 (30 mg/kg), lowered the RVSP in CH+Su mice. Cardiac functional magnetic resonance imaging studies revealed that acute SKA‐31 administration does not alter the heart rate, stroke volume, ejection fraction, and cardiac output. Importantly, the RVSP‐lowering effect of SKA‐31 was not observed in normal mice. Collectively, our data reveal unaltered IK/SK channel activity in PH and provide proof of principle that IK/SK activation can be used as a strategy for lowering PAP in PH.

Endothelial TRPV4 channels and vasodilator reactivity.

Transient receptor potential vanilloid 4 (TRPV4) ion channels on the endothelial cell membrane are widely regarded as a crucial Ca2+ influx pathway that promotes endothelium-dependent vasodilation. The downstream vasodilatory targets of endothelial TRPV4 channels vary among different vascular beds, potentially contributing to endothelial cell heterogeneity. Although numerous studies have examined the role of endothelial TRPV4 channels using specific pharmacological tools over the past decade, their physiological significance remains unclear, mainly due to a lack of endothelium-specific knockouts. Moreover, the loss of endothelium-dependent vasodilation is a significant contributor to vascular dysfunction in cardiovascular disease. The activity of endothelial TRPV4 channels is impaired in cardiovascular disease; therefore, strategies targeting the mechanisms that reduce endothelial TRPV4 channel activity may restore vascular function and provide therapeutic benefit. In this chapter, we discuss endothelial TRPV4 channel-dependent signaling mechanisms, the heterogeneity in endogenous activators and targets of endothelial TRPV4 channels, and the role of endothelial TRPV4 channels in the pathogenesis of cardiovascular diseases. We also discuss potentially interesting future research directions that may provide novel insights into the physiological and pathological roles of endothelial TRPV4 channels.

Microcirculatory alterations after cardiopulmonary bypass as assessed with near infrared spectroscopy: a pilot study

To the Editor, Cardiac surgery under cardiopulmonary bypass (CPB) may induce changes in microvascular perfusion and compromise peripheral tissue oxygenation. Near infrared spectroscopy (NIRS) is an easily applicable noninvasive technique that has been used in combination with the vascular occlusion technique (VOT) for the evaluation of the microcirculation. We hypothesized that NIRS and VOT are able to detect the microcirculatory alterations of cardiac surgical patients. After obtaining institutional ethics approval and written informed consent, we conducted a pilot study in nine cardiac surgery patients (three males/ six females). Characteristics of the patients were: age 67 (13), EuroSCORE 6.4 (3.8), left ventricular ejection fraction 58 (9) %, CPB duration 129 (47) min, aortic cross-clamp time 66 (20) min. All patients were anesthetized and their lungs ventilated in a similar manner throughout the monitoring period. The doses of vasopressors/inotropes and propofol did not change during the monitoring period. Near infrared spectroscopy measurements were performed (InSpectra; Hutchinson Technology, Hutchinson, MN, USA) on the day prior to surgery, postoperatively on admission to the intensive care unit, and every two hours for six hours. Tissue oxygen saturation (StO2%) of the thenar eminence was monitored and a brachial VOT was utilized to better assess the microcirculation with the calculation of the oxygen consumption rate and the reperfusion rate. The results of this pilot study are shown in the accompanying Table. Immediately after CPB there were abnormalities in skeletal muscle tissue oxygenation and utilization which normalized at six hours (Table A). Conversely, the global hemodynamic variables did not change significantly in this six-hour monitoring period (Table B). This pilot study indicates that NIRS can detect microvascular derangements whereas routine global measurements seem to be insensitive. Cardiac surgery with CPB induces physiological alterations: the blood is exposed to artificial surfaces, nonpulsatile flow is the norm, the myocardium is arrested with cold cardioplegic protection, and body temperature is lowered by several degrees. These features, in combination with the surgical trauma, contribute to an intense inflammatory reaction resulting in the activation of endothelial cells, leukocytes, platelets, the complement system, and the coagulation cascade. Endothelial dysfunction and the loss of endothelium-dependent vasodilation can lead to the ‘‘noreflow’’ phenomenon and amplify tissue injury. This report shows that NIRS-derived variables depict this local derangement. The improvement of microcirculatory indices during the ensuing hours can be attributed to the restoration of the microcirculation as the hours after surgery progress. Importantly, this report also shows that routine monitors do not reflect these microvasculature abnormalities. Future studies are needed to investigate the possibility of reversing these NIRS-derived microcirculation variables and whether these are important clinical end points. E.-S. Tripodaki, MD A. Tasoulis, MD I. Vasileiadis, MD S. Nanas, MD (&) Evangelismos Hospital, National and Kapodistrian University of Athens, Athens, Greece e-mail: a-icu@med.uoa.gr

Inflammation, Immunity, and Hypertension

Aprominent pathology textbook used in the United States includes an image illustrating the renal histopathology caused by malignant hypertension. The legend describes striking “onion skin” changes of a renal arteriole. Curiously, a sea of mononuclear inflammatory cells surrounding this arteriole is overlooked both in the legend and in the related text. Moreover, nothing regarding inflammation or immune reactions is discussed. This lack of attention to inflammatory cells is, however, not surprising. Although many experimental studies have implicated inflammation in hypertension, these have largely been performed in experimental animals; there is no proof that inflammation contributes to human hypertension. In fact, some anti-inflammatory or immune-suppressing drugs (eg, nonsteroidal anti-inflammatory drugs and cyclosporine) paradoxically cause hypertension in humans, likely via off-target effects. Often the term “inflammation” is used in the context of cardiovascular disease as a catchall referring to nonspecific phenomena, such as elevation of C-reactive protein or the presence of macrophages in a tissue. Most clinicians and investigators find this vague and difficult to understand. Even more puzzling is that many studies now implicate the adaptive immune response, and in particular, lymphocytes, in hypertension and vascular disease. Traditionally, bacterial, viral, or tumor antigens activate this arm of immune defense. As such, it has been hard to imagine how adaptive immunity could be involved in a disease such as hypertension. In this article, we will attempt to address some of these puzzling questions. We will briefly review components of the innate and adaptive immune response, discuss data from many groups, including our own, that suggest that common forms of hypertension are immune mediated, and provide a working hypothesis of how signals from the central nervous system trigger an immune response that causes hypertension. ### General Concepts Regarding Inflammation and Immunity #### Innate Immunity The first line of defense against pathogens is the innate immune response. Important components of this system include epithelial …

Short-term effect of atorvastatin on ischaemic threshold in hypercholesterolaemic patients with stable ischaemic heart disease

Objective — Hypercholesterolaemia is associated with a loss of endothelium-dependent vasodilation, which may facilitate the occurrence of myocardial ischaemia in patients with coronary artery disease (CAD). The improvement of endothelial dilator function after 4 to 6 weeks of oral lipidlowering therapy has been documented. Whether this early restoration of endothelial function by statins translates into anti-ischaemic effects is unknown.This study was designed to determine the effect of 4 weeks’ treatment with 80 mg atorvastatin daily on exercise-induced ischaemia in patients with stable ischaemic heart disease (IHD) receiving standard anti-anginal drug therapy.Methods and results — A total of 41 patients with documented CAD, exercise-induced ischaemia and LDL-cholesterol > 130 mg/dl underwent exercise ECG, angina score and lipid level assessment at baseline, after 4 weeks of placebo treatment, and after 4 weeks of therapy with atorvastatin 80 mg. Primary endpoint was the change in time to 1 mm ST-segment depression (= ischaemic threshold) between placebo and treatment period.Atorvastatin treatment resulted in a 55% reduction of low-density lipoprotein (LDL) cholesterol (from mean of 162 (SD 32) to 72 (20) mg/dl). For a comparable rate-pressure product, the average time to 1 mm ST-segment depression was 295 (112) s at baseline, 314 (149) s after placebo and 301 (131) s after atorvastatin, indicating that the ischaemic threshold was not significantly modulated after 4 weeks of atorvastatin treatment.There was also no significant change in global angina score or in time to maximal ST-segment depression.Conclusions — High-dose atorvastatin treatment for 4 weeks drastically reduced LDLcholesterol. However, the present study did not demonstrate a significant effect on the ischaemic threshold in patients with stable IHD already under treatment with anti-ischaemic agents.

Molecular mechanisms of impaired endothelial function associated with insulin resistance.

Dysfunction of the endothelium in large- and medium-sized arteries plays a central role in atherogenesis. The insulin resistance syndrome encompasses more than a subnormal response to insulin-mediated glucose disposal. Patients with this syndrome also frequently display elevated blood pressure, hyperlipidemia, and dysfibinolysis, even without any clinically manifested alteration in plasma glucose concentrations. Of note endothelial dysfunction and atherosclerosis also have been demonstrated in patients with hypertension, which is one of the features of the syndrome of insulin resistance. Insulin-induced vasodilation, which is mediated by the release of nitric oxide (NO) release, is impaired in obese individuals who display insulin resistance. Although it is tempting to speculate that loss of endothelium-dependent vasodilation and increased vasoconstriction might be etiological factors of elevated blood pressure, the factors contributing to NO-mediated endothelial dysfunction in the insulin-resistant state are not fully defined. Experimental evidences suggest that (6R)-5,6,7,8-tetrahydrobiopterin (BH(4)), the natural and essential cofactor of NO synthases (NOS), plays a crucial role not only in increasing the rate of NO generation by NOS but also in controlling the formation of superoxide anion (O(2)(-)) in the endothelial cells. Under insulin-resistant conditions where BH(4) levels are suboptimal, in addition to a reduced synthesis of NO, an accelerated inactivation of NO by O(2)(-) within the vascular wall was observed. Furthermore, oral supplementation of BH(4) restored endothelial function and relieved oxidative tissue damage, through activation of eNOS in the aorta of insulin-resistant rats. These results indicate that abnormal pteridine metabolism contributes to causing endothelial dysfunction and the enhancement of vascular oxidative stress in the insulin-resistant state.

Malfunction of Vascular Control in Lifestyle-Related Diseases: Mechanisms Underlying Endothelial Dysfunction in the Insulin-Resistant State

It is tempting to speculate that increased vasoconstriction and loss of endothelium-dependent vasodilation might be etiological factors of elevated blood pressure in the insulin-resistant state. Vascular contraction induced by angiotensin II and the expression of NAD(P)H oxidase were increased in the aorta of insulin-resistant mice. In addition, both angiotensin II type 1 receptor expression and superoxide anion production were up-regulated in these mice. Another mechanism for imparing endothelial function is the uncoupling of endothelial nitric oxide synthase (eNOS). It has become clear from studies on the aorta of insulin-resistant rat that insulin resistance may be a pathogenic factor for endothelial dysfunction through impaired eNOS activity and increased oxidative breakdown of NO (nitric oxide) due to an enhanced formation of superoxide anion (NO/superoxide anion imbalance), which are caused by relative deficiency of tetrahydrobiopterin, a cofactor of NOS, in vascular endothelial cells. Supplementation of tetrahydrobiopterin restored endothelial function and relieved oxidative tissue damage through activation of eNOS in those rats. These results indicate that generation of superoxide anion from NAD(P)H oxidases and an uncoupled eNOS may be pathogenic factors for impaired endothelial function and hypertension in the insulin-resistant state.

Endothelial function, inflammation, and prognosis in cardiovascular disease

The vascular endothelium is an active, dynamic tissue that controls many important functions, including regulation of vascular tone and maintenance of blood circulation, fluidity, coagulation, and inflammatory responses. Cardiovascular risk factors affect many of the normal functions of the endothelium. In particular, oxidized low-density lipoprotein cholesterol initiates a series of events that begin with cell activation, endothelial dysfunction, local inflammation, and a procoagulant vascular surface. These conspire to result in plaque formation and ultimately plaque rupture and cardiovascular events. Endothelial dysfunction may be evaluated by means of invasive techniques, such as coronary artery reactivity to acetylcholine, or noninvasive techniques, such as brachial artery ultrasonography. Loss of endothelium-dependent vasodilation is a characteristic feature throughout the development of atherosclerosis, and it is independently related to future adverse cardiovascular risk. Therefore, measurement of endothelial function can possibly be used to determine risk, to triage management, and to improve outcomes. At the same time, inflammation is a crucial factor in the atherosclerotic disease process. To identify and monitor the ongoing inflammatory process, markers of inflammation such as C-reactive protein (CRP) have been studied. Scientific evidence shows that elevated plasma CRP values add to the predictive ability of other established risk factors; moreover, elevated values appear to augment the Framingham Coronary Risk Score in identifying individuals who should be considered for cardioprotective treatment programs. Interestingly, thiazolidinediones (TZDs), peroxisome proliferator-activated receptor–γ agonists that are effective in the treatment of type 2 diabetes mellitus, not only increase insulin sensitivity but can benefit endothelial function because they exhibit anti-inflammatory effects. For many individuals, including those with the metabolic syndrome and/or type 2 diabetes, endothelial dysfunction and elevated plasma CRP levels indicate increased risk of cardiovascular disease. Notably, the TZDs have been shown to reduce CRP levels and may improve endothelial function.

Effect of inhibition of nitric oxide synthase on the vasopressor response to ephedrine

Ephedrine is a mixed adrenergic agonist, stimulating both alpha- and beta-adrenergic receptors. The effects of ephedrine use include increases in heart rate, cardiac output, peripheral resistance, and blood pressure, and its use is associated with serious cardiovascular events such as stroke, arrhythmias, and myocardial infarction. The vascular endothelium plays a fundamental role in the regulation of vascular tone by releasing vasoactive factors such as nitric oxide (NO). The loss of NO bioactivity, often referred to as endothelial dysfunction, is characterized by the loss of endothelium-dependent vasodilation and is thought to be a common pathway for cardiovascular events such as vasospasm, hypertension, and myocardial infarction. Since endothelial dysfunction is characterized by loss of NO activity, and since ephedrine and endothelial dysfunction may be associated with similar cardiovascular events, the current study was undertaken to determine the effect of inhibition of NO production on responses to ephedrine in the rat. A sodium nitroprusside (SNP) infusion procedure was used to restore baseline vascular parameters to pre-L-NAME levels, allowing for direct comparison of agonist responses before and after NOS inhibition. The results demonstrate that the vascular response to ephedrine in the rat is modulated by NO and that NO production in response to ephedrine may be secondary to beta 2-receptor stimulation.

Mechanisms of Selective Impairment of Nitric Oxide-Mediated Endothelium-Dependent Vasodilation Following Ionizing Irradiation

The endothelium is the main target in the vascular wall for ionizing radiation; an irradiation-induced impairment leads to the loss of endothelium-dependent vasodilation. Recent studies showed that gamma irradiation causes selective impairment of nitric oxide (NO)-mediated vasodilation, but little is known about the underlying mechanisms. The goal of our study was to identify mechanisms underlying the impairment of NO-mediated endothelium-dependent vasodilation after whole-body irradiation with a cobalt60 source. We compared vasodilation and NO release induced by acetylcholine (ACh), as well as relaxations induced by exogenous NO, in the thoracic aorta from healthy and irradiated rabbits. It was shown that despite the loss of relaxation the apparent release of NO induced by ACh and detected by chemiluminescence assay remained unaltered in irradiated tissue, as compared with that of healthy rabbits. At the same time, it was evident that while in healthy vessels relaxation increased with increasing NO concentration;, this relationship was lost in irradiated vessels. Endothelium-denuded aortic smooth muscles from irradiated rabbits retained the same sensitivity to NO gas solution as healthy denuded vessels. When non-denuded vascular tissues were used, irradiated aortas demonstrated an increased sensitivity, as compared with non-irradiated vascular tissue. α-Tocopherol acetate and phosphatidylcholine liposomes, when administered to rabbits 1 h after irradiation, effectively restored the NO-mediated endothelium-dependent relaxation and normalized the relationship between NO release and relaxation and also the sensitivity of the vessels to inhibition by Nω-nitro-L-arginine (L-NA). Taken together, these data allow us to hypothesize that inhibition of an EDRF/NO-dependent component of vascular relaxation in irradiated rabbits may be due to at least two possible reasons: (i) intensified inactivation of endothelium-derived NO by oxygen free radicals, and (ii) abnormalities in diffusion of NO in the irradiated endothelium and subendothelial layer. Both these effects may lead to a decrease in the bioavailability of NO.

Effect of cyclic axial stretch of rat arteries on endothelial cytoskeletal morphology and vascular reactivity

Pulsatile fluid shear stress and circumferential stretch are responsible for the axial alignment of vascular endothelial cells and their actin stress fibers in vivo. We studied the effect of cyclic alterations in axial stretch independent of flow on endothelial cytoskeletal organization in intact arteries and determined if functional alterations accompanied morphologic alterations. Rat renal arteries were axially stretched (20%, 0.5 Hz) around their in vivo lengths, for up to 4 h. Actin stress fibers were examined by immunofluorescent staining. We found that cyclic axial stretching of intact vessels under normal transmural pressure in the absence of shear stress induces within a few hours realignment of endothelial actin stress fibers toward the circumferential direction. Concomitant with this morphologic alteration, the sensitivity (log(EC 50)) to the endothelium-dependent vasodilator (acetylcholine) was significantly decreased in the stretched vessels (after stretching –5.15±0.79 and before stretching –6.71±0.78, resp.), while there was no difference in sodium nitroprusside (SNP) sensitivity. There was no difference in sensitivity to both acetylcholine and SNP in time control vessels. Similar to cultured cells, endothelial cells in intact vessels subjected to cyclic stretching reorganize their actin filaments almost perpendicular to the stretching direction. Accompanying this morphological alteration is a loss of endothelium-dependent vasodilation but not of smooth muscle responsiveness.

Markers for progression of coronary disease.

Endothelial cells play numerous physiologic roles including regulation of vascular tone, regulation of hemostasis and fibrinolysis, regulation of inflammatory processes, and maintenance of a permeability barrier to provide for exchange and active transport of substances into the artery wall. Pathophysiologic stimuli can result in localized alterations in endothelial activity. These changes include increased permeability to plasma lipoproteins, imbalances in local thrombogenic substances causing a prothrombotic state, and release of vasoactive compounds resulting in vasoconstriction. Loss of endothelium-dependent vasodilatation is thought to be an early physiologic event in the development of arteriosclerosis, occurring before morphologic changes in the endothelium can be detected. Much of the effects of healthy endothelium appear to be produced by nitric oxide. Decreased bioavailability of nitric oxide results in endothelial dysfunction, which is the first step in the atherosclerotic process. Risk factor modification and pharmacologic interventions that can reverse endothelial dysfunction have the potential to decrease cardiovascular events in patients at risk.

Hypothermic Storage of Coronary Endothelial Cells Reduces Nitric Oxide Synthase Activity and Expression

Preservation with University of Wisconsin (UW) solution has been implicated in coronary artery endothelial damage and loss of endothelium-dependent vasodilatation. Therefore, the objective of this study was to investigate the effect of this solution on basal nitric oxide (NO) release from porcine coronary endothelial cells (CEC). Cultures were exposed to cold (4°C) storage in UW solution for 6, 8 and 12 h. Parallel cultures were incubated with control medium at 37°C. After treatment, NO release was evaluated by nitrite production, a stable metabolite of NO. Activity of the constitutive endothelial nitric oxide synthase (eNOS) was measured by the conversion [3H]-l-arginine to [3H]-l-citrulline and eNOS protein expression by Western blotting. Nitrite production by control cells was augmented with increasing times of incubation, whereas no change was observed in those cultures preserved with UW solution. Activity of eNOS was significantly decreased compared to the respective control group by cold storage of cells for longer periods than 6 h. Such decrease was correlated with a diminished eNOS protein expression in CEC preserved with UW solution after 8- and 12-h storage. These results suggest that prolonged hypothermic storage of CEC with UW solution does not preserve basal NO release because of a certain loss of eNOS protein, which may contribute to the reported injury of heart transplants after long-term preservation.

Intracavernosal injections of vascular endothelial growth factor protects endothelial dependent corpora cavernosal smooth muscle relaxation in the hypercholesterolemic rabbit: a preliminary study.

Atherosclerosis is a major risk factor for erectile dysfunction, and loss of endothelium-dependent vasodilation appears early in the development of this disorder. Nitric oxide (NO) appears to be the principle mediator of erectile function and is generated in part by the sinusoidal endothelium. Vascular endothelial growth factor (VEGF) is an angiogenic growth factor and an endothelial cell-specific mitogen and the actions of VEGF are coupled to NO. In this preliminary study, we investigated whether VEGF could be used to protect endothelial dependent cavernosal relaxation from the atherosclerotic injury induced by a hypercholesterolemic diet.Two groups of New Zealand white adult male rabbits received a 1% cholesterol diet for four weeks, and two groups consumed normal rabbit chow. Half of the rabbits consuming the 1% cholesterol diet received weekly penile injections of 0.3 mg VEGF (n=8), and half injections of normal saline (n=8). Rabbits fed normal chow followed a similar protocol, half received weekly penile injections of 0.3 mg VEGF (n=6) and half were given weekly penile injections of normal saline (n=6). Isometric tension studies (with norepinephrine, acetylcholine, sodium nitroprusside and histamine) were performed on isolated strips of corpora cavernosa. The degree of corporal smooth muscle relaxation in response to ACH and SNP administration was recorded and compared. Significant elevation in serum total cholesterol levels occurred in rabbits receiving 4 weeks of the 1% cholesterol diet (727+/-75.6 mg/dl vs 38.7+/-5.53 mg/dl) P<0.01. There were no significant differences in cavernosal contraction in any group, while cavernosal smooth muscle from rabbits on normal chow retained the ability to relax in response to ACH and SNP in tissue bath. The hypercholesterolemic rabbits receiving VEGF had a significantly higher maximal per-cent relaxation to ACH (111+/-28.9) compared to the hypercholesterolemic rabbits that received NS (77+/-23.1, P<0.001). This difference in percent maximal relaxation to SNP was also present for hypercholesterolemic/VEGF rabbits (129.4+/-24) versus the hypercholesterolemic/NS rabbits (115.0+/-18, P=0.033). In conclusion, intracavernosal injections of VEGF appear to protect corporal endothelium from hypercholesterolemia induced injury, thus preserving endothelial dependent corporal smooth muscle relaxation in hypercholesterolemic rabbit.

Thermotolerance preserves endothelial vasomotor function during ischemia/reperfusion.

Ischemia/reperfusion (I/R) results in endothelial dysfunction, seen as loss of endothelium-dependent vasodilatation. In prolonged ischemia, this can result in marked vasospasm or no reflow in the microvasculature. Thermotolerance (T) attenuates I/R-induced microvascular injury. The aim of this study was to investigate the effect of thermotolerance on I/R-induced vasomotor changes and "no reflow." Sprague-Dawley rats were randomized into an ischemia/reperfusion group (I/R group) and a group in which thermotolerance (41 + 0.5 degrees C for 15 min 18 h prior to I/R) was induced (T + I/R group). IR injury was established by occlusion of the superior mesenteric and celiac vascular pedicle for 30 min, followed by 60 min of reperfusion. Vasomotor function [arteriolar constriction:dilatation (C:D) ratio] measured by response to acetylcholine (endothelium-dependent) and sodium nitroprusside (endothelium-independent) and "no-reflow" phenomenon were determined in mesenteric arterioles by intravital microscopy. Data are expressed as means +/- SEM and were analyzed using ANOVA and chi(2) test. I/R caused a significant decrease in endothelium-dependent vasodilatation (C:D = 1.37+/-0.31 in IR group vs. 2.06+/-0.20 in baseline, P<0.01) and no reflow in arterioles in 16 of 28 unheated rats. Endothelium-independent dilatation was not altered by I/R. Thermotolerance attenuated this impairment of endothelium-dependent dilatation (P<0.01 vs. IR; C:D = 1.95+/-0.19) and reduced no-reflow phenomenon to 4 of 16 rats (P<0.05 vs. IR). This study demonstrated that thermotolerance preserves endothelial vasomotor function and markedly reduces "no reflow" in arterioles.

Increased pulmonary blood flow produces endothelial cell dysfunction in neonatal swine

Background. The mechanisms by which increased pulmonary blood flow results in pulmonary hypertension have not been determined. Methods. To determine if increased pulmonary blood flow produces endothelial dysfunction that precedes vascular remodeling and smooth muscle proliferation, neonatal swine (n = 12) (age, 6.1 ± 0.5 days) underwent ligation of the left pulmonary artery (LPA) to increase blood flow to the right lung. At 12 weeks of age, endothelium-dependent vasodilatation was assessed by acetylcholine infusion and endothelium-independent vasodilatation by inhaled nitric oxide (NO) in the LPA group and age-matched controls (CON) (n = 11). Results. Mean pulmonary artery pressure was 24.1 ± 3.0 mm Hg in the LPA group and 20.8 ± 1.9 mm Hg in the CON group ( p < 0.1). Pulmonary vascular resistance was 13.2 ± 2.2 Wood units in the LPA group and 5.8 ± 0.8 Wood units in the CON group ( p = 0.001). Acute occlusion of the left pulmonary artery in the CON group increased pulmonary vascular resistance to 6.9 ± 3.9 Wood units ( p = 0.04). Administration of acetylcholine in the CON group after preconstriction with the thromboxane A 2 analogue U46619 resulted in a 30.6% ± 5.4% decrease in pulmonary vascular resistance. In the LPA group, acetylcholine produced paradoxical vasoconstriction and a 15.4% ± 4.1% increase in pulmonary vascular resistance ( p < 0.001 versus CON) indicating loss of endothelium-dependent vasodilatation. Nitric oxide decreased pulmonary vascular resistance by 41.9% ± 3.3% in the CON group and 30.8% ± 2.7% in the LPA group ( p = 0.04 versus CON), indicating preserved endothelium-independent vasodilatation in both groups. Morphometric analysis was performed in 4 animals from each group. Medial wall thickness as percent of external diameter of small arteries (<100 μm) was the same in both groups (6.4% ± 0.4% in the LPA group versus 6.6% ± 0.4% in the CON animals; p > 0.1). Conclusions. Increased pulmonary blood flow in immature animals produces endothelial cell dysfunction with loss of endothelium-dependent vasodilatation before the onset of pulmonary vascular remodeling. Subsequent smooth muscle proliferation may be mediated by endothelium-derived factors.

Hyperhomocysteinemia and atherothrombotic disease.

Hyperhomocysteinemia is an independent risk factor for atherothrombotic disease. The mechanism by which homocysteine induces atherosclerosis and thrombosis is not fully understood. Data on arterial histology in humans with homocystinuria and mild hyperhomocysteinemia are limited. In vitro studies as well as studies in animals and humans indicate that hyperhomocysteinemia induces dysfunction of the vascular endothelium, with loss of endothelium-dependent vasodilation and endothelial antithrombotic properties, and proliferation of vascular smooth muscle cells, which are key processes in current models of atherogenesis and thrombosis. One of the hypotheses is that homocysteine can lead to cellular dysfunction through a mechanism involving oxidative damage but future studies in humans are needed to confirm this. Studies in hyperhomocysteinemic vascular patients have shown that endothelial antithrombotic properties appear to be more severely impaired than in similar patients with normohomocysteinemia. Furthermore, impaired endothelium-dependent vasodilation has been observed in clinically healthy hyperhomocysteinemic subjects in whom no abnormalities were found in endothelial antithrombotic properties. Future studies involving homocysteine-lowering treatment in hyperhomocysteinemic patients with vascular disease and in clinically healthy hyperhomocysteinemic subjects are necessary to investigate the mechanisms by which homocysteine causes atherothrombotic disorders in humans.

Use-Dependent Loss of Acetylcholine- and Bradykinin-Mediated Vasodilation After Nitric Oxide Synthase Inhibition

In the present study, we examined the possibility that the endothelium-dependent vasodilators acetylcholine and bradykinin release preformed pools of nitric oxide-containing factors. Successive injections of selected doses of acetylcholine (1.18 +/- 0.3 micrograms/kg IV) or bradykinin (5 micrograms/kg IV) caused reproducible hypotensive and vasodilator responses within sympathetically intact and sympathetically denervated hindlimbs of conscious rats. After administration of the nitric oxide synthesis inhibitor N omega-nitro-L-arginine methyl ester (L-NAME, 25 mumol/kg IV), the first injection of acetylcholine or bradykinin produced pronounced depressor and vasodilator responses that, in the case of bradykinin, were greater than those observed before L-NAME administration. However, each successive injection of acetylcholine and bradykinin produced progressively smaller responses, such that the later injections elicited a markedly diminished hypotension and vasodilation. This "use-dependent" loss of endothelium-dependent vasodilation was not due to the diminished vasorelaxant potency of nitric oxide-containing factors because the vasodilator effects of the nitric oxide donor sodium nitroprusside (32 micrograms/kg IV) and the S-nitrosothiol compound S-nitro-socysteine (200 nmol/kg IV) were augmented in the presence of L-NAME. These results suggest that the use-dependent loss of the hemodynamic effects of acetylcholine and bradykinin in L-NAME-treated rats may be due to the release and subsequent depletion of a factor whose synthesis depends on the bioavailability of nitric oxide. Taken together, these results suggest that preformed pools of nitric oxide-containing factors exist within the endothelium of resistance vessels and that endothelium-dependent agonists exert their vasorelaxant effects at least in part by the mobilization of these performed pools.

Is the presence of hyperlipidemia associated with impairment of endothelium-dependent neointimal relaxation after percutaneous transluminal coronary angioplasty?

To determine whether hyperlipidemia affects the endothelium-dependent vasomotor response along the dilated vessel after percutaneous transluminal coronary angioplasty (PTCA), we evaluated 32 patients with one-vessel disease, 3-6 months after successful PTCA without restenosis. Fourteen patients had mild stenotic lesions not subjected to PTCA (non-PTCA sites) in addition to the PTCA sites. Vessel diameter changes at 32 PTCA and 36 non-PTCA sites were assessed by quantitative angiography, before and after intracoronary injection of acetylcholine (20 micrograms to the right and 50 micrograms to the left coronary artery) and of nitroglycerin (0.1-0.3 mg). The acetylcholine response ranged from 46% (dilation) to -100% (constriction). All coronary arteries were dilated in response to nitroglycerin, which suggested preservation of the function of vascular smooth muscle, and the presence of an abnormality in endothelial function in those patients with a constrictor response to acetylcholine. There was a negative correlation between the acetylcholine response and the serum total cholesterol level at PTCA sites (r = -0.37; P = 0.038) and at non-PTCA sites (r = -0.46; P = 0.005). These findings indicate that hyperlipidemia is associated with a loss of endothelium-dependent vasodilation, not only at non-PTCA but also at PTCA sites, at which restoration of endothelial function might have occurred. They also suggest that hyperlipidemia may be related to the functional state of the regenerated endothelium at sites where PTCA had been previously performed.

Normalization of abnormal coronary vasomotion by calcium antagonists in patients with hypertension.

Endothelial dysfunction with a loss of endothelium-dependent vasodilation has been reported in patients with arterial hypertension. The purpose of the present study was to evaluate coronary vasomotor response to dynamic exercise in patients with coronary artery disease with and without arterial hypertension and to determine the effect of calcium antagonists on coronary vasomotion. Cross-sectional areas of a normal and a stenotic coronary vessel segment were examined in 79 patients with coronary artery disease at rest and during supine bicycle exercise (Ex). Change in luminal area after acute administration of a calcium antagonist (diltiazem or nicardipine), during exercise, and after sublingual nitroglycerin (percent change compared with rest = 100%) was assessed by biplane quantitative coronary arteriography. Patients were divided into two groups: Group 1 (control) consisted of 48 patients without (normotensive subjects, n = 30; hypertensive subjects, n = 18) and group 2 of 31 patients with (normotensive subjects, n = 15; hypertensive subjects, n = 16) pretreatment with a calcium antagonist immediately before exercise. The groups did not differ with regard to clinical characteristics or hemodynamic data measured during exercise. Mean aortic pressure at rest, however, was significantly increased in hypertensive patients compared with normotensive subjects in group 1 (103 mm Hg versus 92 mm Hg, P < .01) and group 2 (110 mm Hg versus 98 mm Hg, P < .025). In group 1, exercise-induced vasomotor response was significantly different between normotensive and hypertensive patients in normal (+20% versus +1%, P < .003) and stenotic vessels (-5% versus -20%, P < .025). However, in group 2 there was coronary vasodilation in normotensive and hypertensive patients for both normal (delta Ex +23% versus +21%, P = NS) and stenotic vessel segments (+24% versus +26%, P = NS). Abnormal coronary vasomotion during exercise can be observed in hypertensive patients with reduced vasodilator response in normal arteries and enhanced vasoconstrictor response in stenotic arteries. Calcium antagonists prevent the abnormal response of normal and stenotic coronary arteries to exercise in hypertensive patients and thus may compensate for endothelial dysfunction with reduced vasodilator response to exercise.