Endothelium-derived Vasoactive Factors Research Articles

Altered purinergic signaling in uridine adenosine tetraphosphate-induced coronary relaxation in swine with metabolic derangement

We previously demonstrated that uridine adenosine tetraphosphate (Up4A) induces potent and partially endothelium-dependent relaxation in the healthy porcine coronary microvasculature. We subsequently showed that Up4A-induced porcine coronary relaxation was impaired via downregulation of P1 receptors after myocardial infarction. In view of the deleterious effect of metabolic derangement on vascular function, we hypothesized that the coronary vasodilator response to Up4A is impaired in metabolic derangement, and that the involvement of purinergic receptor subtypes and endothelium-derived vasoactive factors (EDVFs) is altered. Coronary small arteries, dissected from the apex of healthy swine and swine 6 months after induction of diabetes with streptozotocin and fed a high-fat diet, were mounted on wire myographs. Up4A (10−9–10−5 M)-induced coronary relaxation was maintained in swine with metabolic derangement compared to normal swine, despite impaired endothelium-dependent relaxation to bradykinin and despite blunted P2X7 receptor and NO-mediated vasodilator influences of Up4A. Moreover, a thromboxane-mediated vasoconstrictor influence was unmasked. In contrast, an increased Up4A-mediated vasodilator influence via P2Y1 receptors was observed, while, in response to Up4A, cytochrome P450 2C9 switched from producing vasoconstrictor to vasodilator metabolites in swine with metabolic derangement. Coronary vascular expression of A2A and P2X7 receptors as well as eNOS, as assessed with real-time PCR, was reduced in swine with metabolic derangement. In conclusion, although the overall coronary vasodilator response to Up4A was maintained in swine with metabolic derangement, the involvement of purinergic receptor subtypes and EDVF was markedly altered, revealing compensatory mechanisms among signaling pathways in Up4A-mediated coronary vasomotor influence in the early phase of metabolic derangement. Future studies are warranted to investigate the effects of severe metabolic derangement on coronary responses to Up4A.

Анализ влияния структурной перестройки промотора гена NOS3 на продукцию вазоактивных эндотелиальных факторов

Анализ влияния структурной перестройки промотора гена NOS3 на продукцию вазоактивных эндотелиальных факторов

Protection of coronary endothelial function during cardiac surgery: potential of targeting endothelial ion channels in cardioprotection.

Vascular endothelium plays a critical role in the control of blood flow by producing vasoactive factors to regulate vascular tone. Ion channels, in particular, K+ channels and Ca2+-permeable channels in endothelial cells, are essential to the production and function of endothelium-derived vasoactive factors. Impairment of coronary endothelial function occurs in open heart surgery that may result in reduction of coronary blood flow and thus in an inadequate myocardial perfusion. Hyperkalemic exposure and concurrent ischemia-reperfusion during cardioplegic intervention compromise NO and EDHF-mediated function and the impairment involves alterations of K+ channels, that is, KATP and KCa, and Ca2+-permeable TRP channels in endothelial cells. Pharmacological modulation of these channels during ischemia-reperfusion and hyperkalemic exposure show promising results on the preservation of NO and EDHF-mediated endothelial function, which suggests the potential of targeting endothelial K+ and TRP channels for myocardial protection during cardiac surgery.

Assessment Of Endothelial Damage and Cardiac Injury In a Mouse Model Mimicking Thrombotic Thrombocytopenic Purpura

Background Thrombotic thrombocytopenic purpura (TTP) is a life-threatening illness caused by deficiency of the Von Willebrand factor (VWF) cleaving protease ADAMTS13. Endothelial injury is believed to be a key initiating event in the pathogenesis leading to platelet activation and formation of platelet-rich thrombi in microvasculature. However, the nature of endothelial injury in TTP is poorly defined and seems to differ among the microvascular territory. Especially, a cardiac injury has recently been identified and hypothesized as a major cause of death in TTP. Methods We used an animal model in which some TTP-like symptoms have been triggered in ADAMTS13 knockout mice (B6.129-ADAMTS13tm1Dgi ) by challenge with 2000 units/kg body weight of recombinant human VWF containing ultra large VWF (rhVWF, Baxter, Vienna Austria). rhVWF was also injected in 6 wild type mice (C57/bl6-B129 WT+VWF) while seven other wild type mice received placebo (WT). Cardiac involvement was assessed by transthoracic echocardiography using validated parameters i.e left ventricular ejection fraction (LVEF), fractional shortening (FS) and cardiac index (CI). Cardiac perfusion was determined by arterial spin labeling MRI (Biospec 47/40 advanced II, Brucker, Ettlingen, Germany). Ex vivo endothelial function analysis in isolated coronary, mesenteric and renal segments were performed using a myograph. Arteries were precontracted by phenylephrine or serotonin and the relaxations induced by increasing concentrations of acetylcholine (receptor-mediated, endothelium-dependent relaxation) or the nitric oxide (NO) donor sodium nitroprusside (SNP; endothelium-independent- relaxation) were assessed. Arteries were also incubated with the NO synthase-inhibitor N-Nitro L-Arginine (LNNA) to assess the contribution of NO to the relaxing responses to acetylcholine (endothelium-dependent NO-independent-relaxation). Results On day 1, VWF-challenged ADAMTS13 KO mice rapidly developed symptoms and severe thrombocytopenia (41.8G/L ± 6.9G/L vs 480.7G/L ± 86.5G/L (WT+VWF) and 1118.6G/L ± 160.8G/L (WT); p<0.001), schistocytosis and a decrease in hematocrit levels (40.9% ± 0.8% vs WT+VWF: 51.3% ± 3,8%; p< 0.05 and WT: 56.1% ± 3%; p< 0.001). On day 2, necropsy revealed that macroscopic lesions were restricted to the heart and consisted of acute myocardial hemorrhage and necrosis. Myocardial necrosis was accompanied by infiltration of lymphocytes and interstitial edema. Minimal, acute tubular necrosis in the kidneys was seen in a few animals. Injection of rhVWF in ADAMTS13 KO mice resulted in a decrease in LVEF (73.8% ± 2.7% vs WT+VWF: 86.6% ± 1.3% and WT: 86.8% ± 1.3%; p< 0.01), in FS (37.3% ± 2.1% vs WT+VWF: 50.1% ± 1.6%; p<0.05 and WT: 50.9% ± 12.8%; p< 0.01) and in CI (1.21 ml/min/g ± 0.09 vs WT+VWF: 1.70 ml/min/g ± 0.14 and WT: 1.66 ml/min/g ± 0.1; p< 0.05) suggesting an early systolic dysfunction. However, cardiac perfusion was not significantly affected on day 2. Administration of rhVWF in ADAMTS13KO mice decreased the NO-mediated relaxing responses to acetylcholine in mesenteric (51.1% ± 14.8% vs WT+VWF: 94.4% ± 1.6%; p< 0.05 and WT: 96.5% ± 2.3%; p< 0.001) and coronary arteries (61.7% ± 12.4% vs WT+VWF: 89.9% ± 6.3% and WT: 96.8% ± 0.9%; p< 0.05) but not in renal arteries. Interestingly, under LNNA, endothelium-dependent relaxations were also markedly affected in coronary arteries (19.3% ± 3.7% vs WT+VWF: 70.2% ± 4.7%; p<0.001) in ADAMTS13KO mice suggesting the role of other endothelium-derived vasoactive factors. In parallel, the relaxing responses to SNP were slightly affected (47.8% ± 13.8% vs WT+VWF: 79.1% ± 13.3% and WT: 80.2% ± 7.2%; p< 0.05), suggesting a strong coronary vascular dysfunction on day 2. Conclusions This experimental study reproduced an animal model in which TTP like symptoms are triggered in ADAMTS13 KO mice by administration of VWF and demonstrated that the heart is the most sensitive target organ with myocardial necrosis and systolic dysfunction. We showed for the first time a strong mesenteric and coronary endothelial dysfunction in an induced-TTP model. It may represent an important trigger of the systemic organs failure occurring in this disease, strengthening the need to define the mechanisms involved in this early vascular injury. Disclosures: Schiviz: Baxter: Employment.

Anaesthesia and cardiopulmonary effects of tiletamine-zolazepam/xylazine/tramadol and its effects on nitric oxide, plasma endothelin, 6-keto-PGF1α and thromboxanes B2 in miniature pigs

This study focused on anaesthesia and cardiopulmonary effects of tiletamine-zolazepam/xylazine/tramadol in miniature pigs and its effects on endothelium-derived vasoactive factors. A total of 14 eight-month-old Chinese experimental miniature pigs were used in this study. Tiletamine-zolazepam (3.5 mg·kg-1), xylazine (1.32 mg·kg-1) and tramadol (1.8 mg·kg-1) were administered i.m.; blood pressure and heart rate were recorded. At the same time, blood was collected through precaval vein, and nitric oxide, endothelin, 6-keto-PGF1α and thromboxanes B2 were determined by colorimetry and radioimmunoassay. The mean times to dorsal recumbency, duration of immobilization, standing and walking were 2.26 ± 0.72, 87.57 ± 9.61, 25.63 ± 12.55 and 36.70 ± 14.53 min, respectively. Blood pressure was significantly changed at 10 and 80 min (P < 0.01), and the heart rate ranged from 89 to 134 bpm without episodes of severe bradycardia or tachycardia. Significantly positive correlation was observed between endothelin, thromboxanes B2 and blood pressure as well as the heart rate (P < 0.05). There was negative correlation between PGI2 and blood pressure as well as heart rate (P < 0.05). The results showed that endothelin, 6-keto-PGF1α and thromboxanes B2 participated in the changing of cardiopulmonary parameters which were caused by tiletamine-zolazepam-xylazine-tramadol anaesthesia in miniature pigs, and the 6-keto-PGF1α, ET and TXB2 concentrations in plasma participated in the changing of blood pressures during anaesthesia. Therefore, we can recommend tiletamine-zolazepam/xylazine/tramadol for anaesthesia in pigs, and this study also contributes to the evaluation of the effect of endothelium-derived vasoactive factors during anaesthesia.

The future of endothelin research: Scientific mentoring and beyond

Endothelium-dependent regulation of vascular tone was one of the key discoveries in physiology in the 1980s, including the characterization of endothelium-derived vasoactive factors such as endothelin. Young investigators, often while starting research as part of their PhD degree, have been instrumental in carrying out the work that led some of the most important discoveries in the endothelin field. This article reviews the importance of mentoring for research in general and for endothelin research in particular, including examples of outstanding young investigators that have been instrumental in some of the key discoveries in the endothelin field. Recognizing scientific excellence among young investigators has a long tradition in the history of the International Conferences on Endothelin. Winners of “Young Investigator Awards” of the past five endothelin conferences (ET-8, ET-9, ET-10, ET-11, and ET-12) are presented, as well as recipients of the “ET-12 Best Presentation Awards” established on the occasion of the Twelfth International Conference on Endothelin ET-12 in Cambridge in September 2011.

Obesity and vascular dysfunction: the fat‐e of rich and poor

Obesity and vascular dysfunction: the fat‐e of rich and poor

Obesity and risk of vascular disease: importance of endothelium-dependent vasoconstriction.

Obesity has become a serious global health issue affecting both adults and children. Recent devolopments in world demographics and declining health status of the world's population indicate that the prevalence of obesity will continue to increase in the next decades. As a disease, obesity has deleterious effects on metabolic homeostasis, and affects numerous organ systems including heart, kidney and the vascular system. Thus, obesity is now regarded as an independent risk factor for atherosclerosis-related diseases such as coronary artery disease, myocardial infarction and stroke. In the arterial system, endothelial cells are both the source and target of factors contributing to atherosclerosis. Endothelial vasoactive factors regulate vascular homeostasis under physiological conditions and maintain basal vascular tone. Obesity results in an imbalance between endothelium-derived vasoactive factors favouring vasoconstriction, cell growth and inflammatory activation. Abnormal regulation of these factors due to endothelial cell dysfunction is both a consequence and a cause of vascular disease processes. Finally, because of the similarities of the vascular pathomechanisms activated, obesity can be considered to cause accelerated, 'premature' vascular aging. Here, we will review some of the pathomechanisms involved in obesity-related activation of endothelium-dependent vasoconstriction, the clinical relevance of obesity-associated vascular risk, and therapeutic interventions using 'endothelial therapy' aiming at maintaining or restoring vascular endothelial health. This article is part of a themed section on Fat and Vascular Responsiveness. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-3.

Effects of PCB126 and 17β-oestradiol on endothelium-derived vasoactive factors in human endothelial cells

Epidemiological and experimental studies suggest an association between elevated serum levels of co-planar PCBs and hypertension, and one study indicate that this effect is dependent on the level of oestrogen. This study investigated the effects of 3,3′,4,4′,5-pentachlorobiphenyl (PCB126) and 17β-oestradiol (E 2) on vasoactive factors in human umbilical vein endothelial cells (HUVEC). The results reveal that PCB126 stimulated the vasoconstriction factors COX-2 and PGF 2α in HUVEC. An up-regulation of COX-2 expression was demonstrated using qRT-PCR, western blot and immunofluorescence and increased production of PGF 2α was demonstrated using LC/MS 2 and enzyme immunoassay. Also, PCB126 slightly increased ROS production and decreased NO production in HUVEC. The addition of E 2 enhanced PCB126-induced transcription of CYP1A1, CYP1B1 and COX-2 in HUVEC whereas an increased transcription of eNOS only occurred following combined treatment with E 2 and PCB126. Immunofluorescence demonstrated that HUVEC expressed AHR and ERβ but lacked ERα and the involvement of AHR and ERβ on the effects of PCB126 was examined by the addition of AHR and ER antagonists. The binding of PCB126 to AHR was critical for the effects of PCB126 whereas the role of ERβ was equivocal. In conclusion, these studies suggest that PCB126 induced changes in human endothelial cells that are characteristic for endothelial dysfunction in human hypertension and that PCB126-induced transcription of genes important for vascular function in human endothelial cells can be elevated by increased oestrogen levels. These findings may help understanding the mechanism for the association between PCB126 exposure and hypertension reported in human subjects and experimental animals.

Endothelium-derived vasoactive factors and hypertension: possible roles in pathogenesis and as treatment targets.

Endothelial cells regulate vascular tone by releasing various contracting and relaxing factors including nitric oxide (NO), arachidonic acid metabolites (derived from cyclooxygenases, lipoxygenases, and cytochrome P450 monooxygenases), reactive oxygen species, and vasoactive peptides. Additionally, another pathway associated with the hyperpolarization of the underlying smooth muscle cells plays a predominant role in resistance arteries. Endothelial dysfunction is a multifaceted disorder, which has been associated with hypertension of diverse etiologies, involving not only alterations of the L-arginine NO-synthase–soluble guanylyl cyclase pathway but also reduced endothelium-dependent hyperpolarizations and enhanced production of contracting factors, particularly vasoconstrictor prostanoids. This brief review highlights these different endothelial pathways as potential drug targets for novel treatments in hypertension and the associated endothelial dysfunction and end-organ damage.

Buyang Huanwu decoction ameliorates coronary heart disease with Qi deficiency and blood stasis syndrome by reducing CRP and CD40 in rats

Ethnopharmacological relevance Qi deficiency and blood stasis is traditional Chinese medicine (TCM) syndrome. It leads to many diseases including coronary heart diseases (CHD) and cerebrovascular diseases (CVD). Inflammatory biomarkers and many endothelium-derived vasoactive factors are considered to play pivotal roles in CHD. Buyang Huanwu decoction (BYHWD), a TCM formula, has been recognized as a treatment for CHD with Qi deficiency and blood stasis syndrome and CVD in clinic. The mechanisms of BYHWD effect on CHD with Qi deficiency and blood stasis syndrome are unclear. Aim of the study The aim is to investigate whether the effects of BYHWD on CHD with Qi deficiency and blood stasis syndrome in rats are associated with the inhibition of CRP, CD40 and vascular endothelial regulators. Materials and methods The treated groups were lavaged with 25.68, 12.84 and 6.42 g/kg BYHWD respectively once a day for 21 days. The level of C-reactive protein (CRP) in serum and the expression of cluster of differentiation 40 (CD40) in the heart and aorta of rats were detected. Moreover, the levels of thromboxaneA 2 (TXA 2) and prostacyclin (PGI 2) in plasma were measured and the levels of inducible nitric oxide synthase (iNOS) and endothelial nitric oxide synthase (eNOS) in serum were detected. Results BYHWD (25.68 g/kg) significantly decreased the level of CRP in serum and BYHWD (25.68 and 12.84 g/kg) decreased the expression of CD40 in the heart and aorta ( P < 0.01). The results also revealed that BYHWD (25.68 g/kg) inhibited the levels of iNOS in serum and TXA 2 in plasma and increased the levels of eNOS in serum and PGI 2 in plasma ( P < 0.01). Conclusion The study shows that the ameliorative effects of BYHWD on CHD with Qi deficiency and blood stasis syndrome in rats are associated with the inhibition of CRP and CD40 and the regulation of endothelium-derived vasoactive factors.

Sphingolipids and the orchestration of endothelium-derived vasoactive factors: when endothelial function demands greasing.

Vasomotor tone is regulated by a complex interplay of a variety of extrinsic neurohumoral and intrinsic factors. It is the endothelium that has a major influence on smooth muscle cell tone via the release of intrinsic vasoactive factors and is therefore an important regulator of vasomotor tone. Sphingolipids are an emerging class of lipid mediators with important physiological properties. In the last two decades it has not only become increasingly clear that sphingolipid signaling plays a pivotal role in immune function, but also its role in the vascular system is now becoming more recognized. In this mini-review we will highlight the possible cross-talk between sphingolipids and intrinsic vasoactive factors released by the endothelium. Via this cross-talk sphingolipids can orchestrate vasomotor tone and may therefore also be involved in the pathophysiology of disease states associated with endothelial dysfunction.

α5β1 Integrin Engagement Increases Large Conductance, Ca2+-activated K+ Channel Current and Ca2+ Sensitivity through c-src-mediated Channel Phosphorylation

Large conductance, calcium-activated K(+) (BK) channels are important regulators of cell excitability and recognized targets of intracellular kinases. BK channel modulation by tyrosine kinases, including focal adhesion kinase and c-src, suggests their potential involvement in integrin signaling. Recently, we found that fibronectin, an endogenous alpha5beta1 integrin ligand, enhances BK channel current through both Ca(2+)- and phosphorylation-dependent mechanisms in vascular smooth muscle. Here, we show that macroscopic currents from HEK 293 cells expressing murine BK channel alpha-subunits (mSlo) are acutely potentiated following alpha5beta1 integrin activation. The effect occurs in a Ca(2+)-dependent manner, 1-3 min after integrin engagement. After integrin activation, normalized conductance-voltage relations for mSlo are left-shifted at free Ca(2+) concentrations >or=1 microm. Overexpression of human c-src with mSlo, in the absence of integrin activation, leads to similar shifts in mSlo Ca(2+) sensitivity, whereas overexpression of catalytically inactive c-src blocks integrin-induced potentiation. However, neither integrin activation nor c-src overexpression potentiates current in BK channels containing a point mutation at Tyr-766. Biochemical tests confirmed the critical importance of residue Tyr-766 in integrin-induced channel phosphorylation. Thus, BK channel activity is enhanced by alpha5beta1 integrin activation, likely through an intracellular signaling pathway involving c-src phosphorylation of the channel alpha-subunit at Tyr-766. The net result is increased current amplitude, enhanced Ca(2+) sensitivity, and rate of activation of the BK channel, which would collectively promote smooth muscle hyperpolarization in response to integrin-extracellular matrix interactions.

Tanshinone II A elicited vasodilation in rat coronary arteriole: Roles of nitric oxide and potassium channels

Salvia miltiorrhiza has been widely used in the treatment of various cardiovascular diseases due to its ability to improve coronary microcirculation and increase coronary blood flow. Tanshinone II A, the major active lipophilic ingredient responsible for the beneficial actions of Salvia miltiorrhiza, was shown to induce vasodilation in coronary arteries. But its effects on coronary arterioles remain unknown. The purpose of this study was to investigate the effects of tanshinone II A on isolated rat coronary arteriole and the underlying mechanisms. Coronary arterioles were carefully dissected, cannulated and pressurized. Tanshinone II A-elicited vascular inner diameter change was recorded by a computerized diameter tracking system. To investigate the mechanisms governing the vasodilative effects of tanshinone II A, the roles of endothelium, endothelium-derived vasoactive factors and potassium channels were assessed respectively. Endothelium denudation, inhibition of nitric oxide synthase (NOS), inhibition of the cytochrome P450 epoxygenase, and blockade of the large conductance calcium(Ca 2+)-activated potassium channels (BKca) significantly decreased the vasodilation elicited by Tanshinone II A. The results indicated that tanshinone II A induces an endothelium-dependent vasodilation in coronary arterioles; nitric oxide (NO) and cytochrome P450 metabolites contribute to the vasodilation; activation of BKca channels plays an important role in the vasodilation.

Exercise Training-Associated Changes in Arterial Stiffness and Endothelium-Derived Vasoactive Factors

Age- and lifestyle-related arterial stiffening is a well-established independent cardiovascular risk factor. Previous studies have investigated the effects of exercise training on arterial stiffness. Aerobic exercise training reduces arterial stiffness. On the other hand, muscle-strengthening exercise, such as weight training, may stiffen central elastic arteries. However, the mechanism underlying exercise training-associated changes in arterial stiffness has not been fully elucidated. Adaptations of arteries to exercise training may, at least partly, be regulated by local factors. We have focused on endothelium-derived vasoactive factors, such as nitric oxide (NO) and endothelin (ET)-1, because the endothelium regulates vascular tone. NO has a significant vasodilatory effect, and ET-1 is a potent vasoconstrictor. Both factors have been reported to be affected by exercise training. This article reviews literature investigating the effects of exercise training on arterial stiffness and the role of endothelium-derived factors. We discuss here the role of endothelial function in exercise training-induced changes in arterial stiffness.

Counterpoint: Chronic Hypoxia-induced Pulmonary Hypertension does not Lead to Loss of Pulmonary Vasculature

Exposure of native sea level dwellers to chronic hypoxia due to migration to high altitude leads to the development of increased pulmonary vascular resistance causing pulmonary hypertension. In some susceptible individuals this progressively worsens causing right ventricular failure and ultimately

Beneficial Effects of Statins on Endothelial Dysfunction and Vascular Stiffness

Endothelial dysfunction and increased arterial stiffness are considered independent predictors of cardiovascular risk. Endothelial dysfunction primarily reflects decreased availability of nitric oxide, a critical endothelium-derived vasoactive factor with vasodilatory and anti-atherosclerotic properties. Techniques for assessing endothelial dysfunction include ultrasonographic measurement of flow-mediated vasodilatation of the brachial artery and plethysmographic measurement of forearm blood flow responses to vasoactive agents. Arterial stiffness can be assessed using pulse wave analysis to generate measures of pulse wave velocity, arterial compliance and wave reflection. It has been demonstrated that the preventive effect of statins on coronary events is not only attributed to cholesterol-lowering, but also to various effects on the vascular wall, which include improved endothelial function as well as antioxidant and anti-inflammatory activity. Previous studies have reported improvement of arterial stiffness by the antioxidant and anti-inflammatory effects of statin therapy in patients with or without hypercholesterolemia. The present review considers the pathophysiology underlying endothelial dysfunction and increased arterial stiffness associated with atherosclerotic disease and the beneficial effects of statins on these markers of atherosclerosis.

Tamoxifen and estrogen attenuate enhanced vascular reactivity induced by estrogen deficiency in rat carotid arteries

Recent clinical trials showed that estrogen usage in postmenopausal women did not affect coronary heart disease incidence, in contrast to several laboratory studies showing that estrogen decreased vascular reactivity. We speculated that, in some arteries, estrogen deficiency enhances endothelial function to compensate for the increased vascular smooth muscle reactivity. In this study, we examined the role of endothelium-derived vasoactive factors and the influence of in vivo estrogen and/or tamoxifen treatment on vascular reactivity of estrogen-deficient rats. Common carotid arteries were isolated from sham-operated (control), ovariectomized (Ovx), estrogen- or tamoxifen-treated Ovx rats, and Ovx rats co-treated with estrogen and tamoxifen. U46619 or phenylephrine induced similar contractions in endothelium-intact rings from all groups. Interestingly, removal of endothelium unmasked enhanced contractions in Ovx rats, which was prevented by estrogen, tamoxifen, or estrogen+tamoxifen treatment. Contractions to high K+ were higher in both endothelium-intact and endothelium-denuded arteries from Ovx rats. Estrogen or tamoxifen treatment normalized high K+-induced contraction. A gap junction blocker, 18α-glycyrrhetinic acid, revealed enhanced contractions to U46619 in the absence or presence of l-NNA. Western blotting showed enhanced expressions of gap junctional connexin 43 in Ovx group. This study suggests that ovariectomy increases functional expression of gap junction-mediated endothelium-derived hyperpolarizing factor. Also, vascular effects of ovariectomy can be reversed by estrogen, tamoxifen or estrogen+tamoxifen treatment, suggesting that tamoxifen confers estrogenic effects in the vascular system.

Chronic estrogen treatment reduces vaso-constrictor responses in insulin resistant rats

Previous experiments have shown that chronic estrogen treatment via subcutaneous implants prevented insulin-induced blood pressure elevation and increased insulin sensitivity in ovariectomized female rats. In vitro vascular studies were performed using isolated mesenteric arteries to determine the effect of chronic estrogen and insulin treatments on vascular responses to vasoconstrictor agents. Female Wistar rats were assigned to the following groups: sham-operated, sham-operated plus insulin, sham-operated plus insulin plus estrogen, ovariectomized, ovariectomized plus insulin, and ovariectomized plus insulin plus estrogen. Chronic insulin and estrogen treatments were initiated with subcutaneous placement of insulin implants (2 U/d) and 17beta-estradiol implants (0.5 mg/pellet, 60 day release) at the back of the neck. After 8 weeks of treatment, mesenteric arteries were isolated for assessment of constrictor responses to norepinephrine and the thromboxane A2 analogue U46619 in the presence or absence of the endothelium. The results show that chronic estrogen treatment attenuated the vascular constrictor responses to norepinephrine and U46619 only in endothelium intact vessels. Incubation with insulin did not significantly affect norepinephrine-induced vascular smooth muscle contraction. The study provides evidence that the mechanism by which estrogen prevents insulin-induced blood pressure elevation in insulin-treated ovariectomized rats is by influencing endothelium-derived vasoactive factors such as thromboxane A2.

Mechanisms, Significance and Treatment of Vascular Dysfunction in Type 2 Diabetes Mellitus

Endothelial dysfunction and increased arterial stiffness occur early in the pathogenesis of diabetic vasculopathy. They are both powerful independent predictors of cardiovascular risk. Advances in non-invasive methodologies have led to widespread clinical investigation of these abnormalities in diabetes mellitus, generating a wealth of new knowledge concerning the mechanisms of vascular dysfunction, risk factor associations and potential treatment targets. Endothelial dysfunction primarily reflects decreased availability of nitric oxide (NO), a critical endothelium-derived vasoactive factor with vasodilatory and anti-atherosclerotic properties. Techniques for assessing endothelial dysfunction include ultrasonographic measurement of flow-mediated vasodilatation of the brachial artery and plethysmography measurement of forearm blood flow responses to vasoactive agents. Arterial stiffness may be assessed using pulse wave analysis to generate measures of pulse wave velocity, arterial compliance and wave reflection. The pathogenesis of endothelial dysfunction in type 2 diabetes is multifactorial, with principal contributors being oxidative stress, dyslipidaemia and hyperglycaemia. Elevated blood glucose levels drive production of reactive oxidant species (ROS) via multiple pathways, resulting in uncoupling of mitochondrial oxidative phosphorylation and endothelial NO synthase (eNOS) activity, reducing NO availability and generating further ROS. Hyperglycaemia also contributes to accelerated arterial stiffening by increasing formation of advanced glycation end-products (AGEs), which alter vessel wall structure and function. Diabetic dyslipidaemia is characterised by accumulation of triglyceride-rich lipoproteins, small dense low-density lipoprotein (LDL) particles, reduced high-density lipoprotein (HDL)-cholesterol and increased postprandial free fatty acid flux. These lipid abnormalities contribute to increasing oxidative stress and may directly inhibit eNOS activity. Although lipid-regulating agents such as HMG-CoA reductase inhibitors (statins), fibric acid derivatives (fibrates) and fish oils are used to treat diabetic dyslipidaemia, their impact on vascular function is less clear. Studies in type 2 diabetes have yielded inconsistent results, but this may reflect sampling variation and the potential over-riding influence of oxidative stress, dysglycaemia and insulin resistance on endothelial dysfunction. Results of positive intervention trials suggest that improvement in vascular function is mediated by both lipid and non-lipid mechanisms, including anti-inflammatory, anti-oxidative and direct effects on the arterial wall. Other treatments, such as renin-angiotensin-aldosterone system antagonists, insulin sensitisers and lifestyle-based interventions, have shown beneficial effects on vascular function in type 2 diabetes. Novel approaches, targeting eNOS and AGEs, are under development, as are new lipid-regulating therapies that more effectively lower LDL-cholesterol and raise HDL-cholesterol. Combination therapy may potentially increase therapeutic efficacy and permit use of lower doses, thereby reducing the risk of adverse drug effects and interactions. Concomitant treatments that specifically target oxidative stress may also improve endothelial dysfunction in diabetes. Vascular function studies can be used to explore the therapeutic potential and mechanisms of action of new and established interventions, and provide useful surrogate measures for cardiovascular endpoints in clinical trials.