Differential contribution of endothelium-derived relaxing factors to vascular reactivity in conduit and resistance arteries from normotensive and hypertensive rats

The endothelium contributes to the maintenance of vasodilator tone by releasing nitric oxide (NO), prostacyclin (PGI₂), and endothelium-derived hyperpolarizing factor (EDHF). In hypertension, endothelium-dependent relaxation is attenuated (a phenomenon referred to as endothelial dysfunction) and contributes to the increased peripheral resistance. However, which vasodilator among NO, PGI₂, and EDHF is impaired in hypertension remains largely unknown. The present study was designed to study the exact contribution of NO, PGI₂, and EDHF to vascular reactivity in conduit and resistance artery, under physiological and pathological conditions. The aorta and the second-order mesenteric artery from spontaneous hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats were used to measure the vasorelaxation with myograph technology, in the presence or absence of different inhibitors. The results showed that the endothelium-dependent vasodilatation in the conduit artery was mediated mainly by NO, whereas the resistant artery by NO, PGI₂, and EDHF together. In hypertension, both NO-mediated relaxation in the conduit artery and NO-, PGI₂-, and EDHF-mediated dilation in the resistant artery were markedly impaired. Furthermore, the endothelium-dependent and the endothelium-independent vasorelaxation in conduit artery was attenuated more pronouncedly than that in the resistant artery from hypertensive rats, suggesting that the conduit artery is more vulnerable to hypertensive condition. In conclusion, vasodilators including NO, PGI₂, and EDHF contribute distinctively to endothelium-dependent relaxation in conduit and resistance artery under physiological and pathological conditions.     

Chronic ET(A) receptor blockade prevents endothelial dysfunction of small arteries in apolipoprotein E-deficient mice

OBJECTIVE: This study investigated whether endothelial dysfunction occurs in mesenteric arteries of apoE-deficient mice and determined the role of endothelin (ET)-1, which is increased in human atherosclerosis, using an orally active endothelin ET(A) receptor antagonist. METHODS: ApoE-deficient and C57BL/6J control mice were fed for 30 weeks with normal chow or high-fat Western-type diet alone or in combination with darusentan (LU135252; 50 mg/kg/day). Vasomotor reactivity of isolated small mesenteric arteries (I.D. 200-250 microm) was studied in vitro under perfused and pressurized conditions. RESULTS: In both mouse strains, about one fourth of the endothelium-dependent relaxant response to acetylcholine was insensitive to inhibition by L-NAME and indomethacin. In mesenteric arteries of apoE-deficient mice on Western-type diet, increased intima-media thickness and levels of endothelin-1 protein were observed. In addition, NO-mediated endothelium-dependent relaxation to acetylcholine was reduced without affecting L-NAME/indomethacin insensitive relaxation and contractions to endothelin-1 and serotonin were enhanced. Treatment with darusentan normalized vascular structure, NO-mediated relaxation to acetylcholine and contractions to endothelin-1 and serotonin without affecting blood pressure or plasma cholesterol levels. CONCLUSIONS: Severe hypercholesterolemia in apoE-deficient mice is associated with attenuation of NO-mediated relaxation to acetylcholine and increased vascular endothelin-1 content. Chronic ET(A) receptor blockade may provide a new therapeutic approach to improve NO-mediated endothelium-dependent vasomotion in small arteries.     

Endothelium-dependent relaxation in experimental atherosclerosis in the rabbit

The effect of feeding a diet supplemented with lipids and containing 2% cholesterol on the endothelium-dependent relaxation of rabbit aorta to acetylcholine was assessed. The effect of feeding a standard rabbit diet after an initial period of 2% cholesterol feeding was assessed also. Age-matched male, New Zealand white rabbits were fed either a 2% cholesterol diet or a standard rabbit diet. The animals were anesthetized with pentobarbitone sodium (25 mg/kg) and killed either at the beginning of the study (0 weeks) or at 4, 8, or 10 weeks. The animals in the reversal study were fed the 2% cholesterol diet for 6 weeks and killed after an additional 14 and 32 weeks on standard diet. The extent of atherosclerosis in the aorta was assessed by Sudan Red staining, estimation of tissue cholesterol, and light and electron microscopy. The relaxation response to acetylcholine was measured in rings of the thoracic aorta following precontraction with norepinephrine (-6.0 log mol/l). The relaxation was significantly impaired in aortas from rabbits fed the 2% cholesterol diet compared to aortas from animals fed the standard diet. The impairment of relaxation was apparent as early as 4 weeks after the start of the 2% cholesterol diet and remained impaired over the next 6 weeks. No improvement in endothelium-dependent relaxation was seen in rabbits on the reversal diet for 14 and 32 weeks. Thus, endothelium-dependent relaxation is attenuated in animals fed a 2% cholesterol diet, and the loss of relaxation persists for at least 32 weeks after the animals are returned to a standard diet.     

Antioxidant improves smooth muscle sarco/endoplasmic reticulum Ca(2+)-ATPase function and lowers tyrosine nitration in hypercholesterolemia and improves nitric oxide-induced relaxation

Antioxidants improve endothelial function in hypercholesterolemia (HC); however, whether this includes improvement of the vascular smooth muscle response to NO is unknown. NO relaxes arteries, in part, by stimulating Ca(2+) uptake via sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) in aortic smooth muscle, and HC impairs SERCA function and the response to NO. HC induces oxidative stress, which could impair SERCA function. To study the effect of antioxidants, which are known to improve endothelium-dependent relaxation in HC, smooth muscle SERCA activity and NO-induced relaxation were studied in rabbits fed normal chow or a 0.5% cholesterol diet for 13 weeks. The antioxidant t-butylhydroxytoluene (BHT, 1%) was mixed with the HC diet in the last 3 weeks. HC impaired acetylcholine- and NO-induced relaxation, and these were restored by BHT. After inhibiting SERCA with thapsigargin, no difference existed in NO-induced relaxation among the three groups. Reduced aortic SERCA activity in HC was restored by BHT without changing SERCA protein expression. 3-Nitrotyrosine was notably increased in the media of the HC aorta, where it colocalized with SERCA. Tyrosine-nitrated SERCA protein was immunoprecipitated in the aortas of HC rabbits, where it was decreased by BHT, and it was also detected in the aortas of atherosclerotic humans. Thus, the antioxidant reverses impaired smooth muscle SERCA function in HC, and this is correlated with the improved relaxation to NO. These beneficial effects may depend on reducing the direct effects on SERCA of reactive oxygen species that are augmented in HC.     

Reduction of NO- and EDHF-mediated vasodilatation in hypertension: role of asymmetric dimethylarginine

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide (NO) synthase (NOS), and endothelial dysfunction is related to the elevation of ADMA level in hypertension. Besides the NO-mediated pathway, the endothelium-derived hyperpolarizing factor (EDHF)-mediated pathway is involved in endothelial dysfunction. The aims of the present study were to evaluate the changes of endothelium-dependent dilatation of arteries in hypertension and the role of ADMA in NO- and EDHF-mediated vasodilatation. The great omental arteries were isolated from essential hypertensive and normotensive patients, and mesenteric arteries were isolated from spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats. NO-, EDHF-, and prostaglandin (PGI(2))-mediated endothelium-dependent vasodilatation were measured, and plasma concentrations of ADMA were determined in rats. Cultured endothelial cells were treated with ADMA (1-10 microM) for 48 h, and the mRNA and protein level of small-conductance Ca(2+)-activated K(+) channel 3 (SK3), which has been thought to be a key mediator of EDHF, was determined. Both NO- and EDHF-mediated endothelium-dependent responses were decreased in the great omental arteries of hypertensive patients and mesenteric arteries of SHR. Plasma levels of ADMA were significantly increased in SHR. In cultured endothelial cells, the expressions of SK3 mRNA and protein were concentration-dependently down-regulated in the presence of ADMA. The present study suggests that the inhibitory effect of ADMA on endothelial function not only involves NO-mediated endothelium-dependent vasodilatation but also the EDHF-mediated pathways in hypertensive animals and humans, and that ADMA can down-regulate the expression of SK3 channels in endothelial cells.     

Free radical production in endothelial cells as a pathogenetic factor for vascular dysfunction in the insulin resistance state

Impairment of nitric oxide-dependent vascular relaxation is a characteristic feature of the insulin-resistant state. To understand those mechanisms, we examined imbalance of O2-/NO production in aortic endothelial cells obtained from high fructose-fed, exogenous hyperinsulinemic, and control rats. Aortic segments from both high fructose-fed and insulin-treated rats produced a 4-fold more O2- than control rats evaluated by a chemiluminescence method. The O2- production in the aortas of both high fructose-fed and insulin-treated rats was mediated through activation of NADH/NADPH oxidase. In isometric tension studies, high fructose vessels with endothelium elicited impaired relaxation in response to acetylcholine or a calcium ionophore A23187 when compared with control rats, whereas these impaired vascular responses were not found in insulin-treated rats. Furthermore, endothelial constitutive NO synthase activity was increased in vessels from insulin-treated rats, but decreased in vessels from high fructose-fed rats. These results indicate that relative excess of O2- production through activation of NADH/NADPH oxidase over NO generation in endothelial cells may contribute to impaired endothelial-dependent relaxation in insulin-resistant state.     

Reduction of NO- and EDHF-Mediated Vasodilatation in Hypertension: Role of Asymmetric Dimethylarginine

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide (NO) synthase (NOS), and endothelial dysfunction is related to the elevation of ADMA level in hypertension. Besides the NO-mediated pathway, the endothelium-derived hyperpolarizing factor (EDHF)-mediated pathway is involved in endothelial dysfunction. The aims of the present study were to evaluate the changes of endothelium-dependent dilatation of arteries in hypertension and the role of ADMA in NO- and EDHF-mediated vasodilatation. The great omental arteries were isolated from essential hypertensive and normotensive patients, and mesenteric arteries were isolated from spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats. NO-, EDHF-, and prostaglandin (PGI₂)-mediated endothelium-dependent vasodilatation were measured, and plasma concentrations of ADMA were determined in rats. Cultured endothelial cells were treated with ADMA (1–10 μM) for 48 h, and the mRNA and protein level of small-conductance Ca²⁺-activated K⁺ channel 3 (SK3), which has been thought to be a key mediator of EDHF, was determined. Both NO- and EDHF-mediated endothelium-dependent responses were decreased in the great omental arteries of hypertensive patients and mesenteric arteries of SHR. Plasma levels of ADMA were significantly increased in SHR. In cultured endothelial cells, the expressions of SK3 mRNA and protein were concentration-dependently down-regulated in the presence of ADMA. The present study suggests that the inhibitory effect of ADMA on endothelial function not only involves NO-mediated endothelium-dependent vasodilatation but also the EDHF-mediated pathways in hypertensive animals and humans, and that ADMA can down-regulate the expression of SK3 channels in endothelial cells.     

Fenofibrate improves age-related endothelial dysfunction in rat resistance arteries

This study was designed to test the hypothesis that fenofibrate, the peroxisome proliferator-activated receptor alpha (PPARalpha) activator, improves age-related endothelial dysfunction in small mesenteric arteries (SMA). Adult and aged rats were treated with fenofibrate and then endothelium-dependent relaxations of SMA; expressions of endothelial NO synthase (eNOS), cyclo-oxygenase (COX-1 and COX-2) and superoxide dismutases (SOD) (Cu/Zn SOD, Mn SOD and EC SOD) proteins and release of TXB(2) and 6-keto-PGF(1alpha) were assessed. Fenofibrate improved endothelium-dependent vasodilatation of arteries from old rats and decreased participation of endothelial vasoconstrictor products, sensitive to COX-1 and COX-2 inhibitors and acting on Tp receptor. Fenofibrate decreased expressions of COX-1 and COX-2, and generation of TXA(2). Release of vasodilator PGI(2) and U46619-induced contraction remained unaltered. Neither NO-mediated vasodilatation nor eNOS expression was affected. The addition of the scavengers, SOD and catalase increased relaxation only in SMA from control rats. Finally, fenofibrate did not change expressions of Cu/Zn SOD and Mn SOD but it increased EC SOD towards that observed in arteries from adult rats. Fenofibrate improves endothelial function in resistance arteries from aged rats by decreasing expression of COX-1 and COX-2 together with enhancing anti-oxidant capacity of the vessel wall probably through the increased expression of EC SOD. This study provides evidence that PPARalpha may have clinical applications toward maintaining endothelial function during ageing.     

Lacidipine prevents endothelial dysfunction in salt-loaded stroke-prone hypertensive rats

Endothelium-dependent vasorelaxation is defective in hypertensive rats, especially in conduit arteries. In the stroke-prone spontaneously hypertensive rat, impaired endothelium-dependent vasorelaxation appears to contribute to the pathogenesis of stroke independent of blood pressure. Because treatment with lacidipine, a long-acting calcium channel blocker, protects against stroke and cardiovascular remodeling in this model, we investigated the effect of this treatment on endothelium-dependent vasorelaxation in the aorta. Stroke-prone rats were exposed to a salt-rich diet (1% NaCl in drinking water) with or without lacidipine (1 mg. kg(-1). d(-1)) for 6 weeks. A high-sodium diet (1) increased systolic blood pressure, aortic weight, and wall thickness and plasma renin activity (P<0.05); (2) markedly reduced nitric oxide (NO)-mediated, endothelium-dependent relaxation of aortic rings to acetylcholine and the sensitivity to the relaxing effect of S-nitroso-N-acetylpenicillamine, an NO donor (P<0.001); and (3) induced an elevation of preproendothelin-1 mRNA levels in aortic tissue (P<0.01) without affecting endothelial NO synthase mRNA levels. Lacidipine treatment prevented the salt-dependent functional and structural alterations of the aorta, including the overexpression of the preproendothelin-1 gene, and increased endothelial NO synthase mRNA levels in aortic tissue (P<0.01). In conclusion, lacidipine protects stroke-prone hypertensive rats against the impairment of endothelium-dependent vasorelaxation evoked by a salt-rich diet, and this effect may contribute to its beneficial effect against end-organ damage and stroke.     

Upregulation of endothelium-derived hyperpolarizing factor compensates for the loss of nitric oxide in mesenteric arteries of Dahl salt-sensitive hypertensive rats

This study was designed to determine whether a high-salt diet would alter endothelial function and, if so, the relative contributions of endothelium-derived hyperpolarizing factor (EDHF) and nitric oxide (NO) to any changes in vasomotor responses. Male Dahl salt-sensitive (DS) rats were given either a high-salt diet (8% NaCl, DS-H) or a low-salt diet (0.4% NaCl, DS-L) for 6 weeks. Membrane potentials and contractile responses were recorded from the isolated superior mesenteric arteries. After salt loading, DS-H developed hypertension, while DS-L remained normotensive. No difference was found in acetylcholine (ACh)-induced, endothelium-dependent relaxation between the groups. However, after treatment with indomethacin and NO synthase inhibitor, EDHF-like relaxation was significantly greater in DS-H than in DS-L. In contrast, NO-mediated relaxation was significantly smaller in DS-Hthan in DS-L. Iberiotoxin (IbTx), a specific blocker of large-conductance calcium-dependent potassium (BKCa) channels, attenuated EDHF-like relaxation in DS-H but not in DS-L. IbTx marginally inhibited EDHF-mediated hyperpolarization only in DS-H. Endothelium-independent relaxation in response to sodium nitroprusside or levcromakalim was similar in both groups. In conclusion, EDHF-like relaxation is upregulated through the activation of BKCa channels in the mesenteric arteries of DS-H. As the overall relaxation in response to ACh did not differ between the groups, the upregulation of EDHF appears to compensate for the loss of NO in the mesenteric arteries of DS-H.     

Uncoupled endothelial nitric oxide synthase and oxidative stress in a rat model of pregnancy-induced hypertension

BACKGROUND: Preeclampsia is a human pregnancy-associated syndrome associated with hypertension, proteinuria, and endothelial dysfunction. We tested whether increased reactive oxygen species (superoxide and peroxynitrite) production and decreased bioavailability of the endothelial nitric oxide (NO) synthase (eNOS) cofactor tetrahydrobiopterin (BH4) contributes to maternal endothelial dysfunction in rats with pregnancy-induced hypertension and several characteristics of preeclampsia. METHODS: Nonpregnant (DS) and pregnant (PDS) rats were treated with deoxycorticosterone acetate and 0.9% saline for approximately 3 weeks and nonpregnant (Con) and pregnant (P) rats received tap water. Blood pressure, urinary protein levels, mesenteric vascular reactivity, aortic protein expression, and aortic reactive oxygen species levels were compared between the four groups. RESULTS: The PDS rats had significantly decreased mesenteric endothelium-dependent relaxation responses and aortic NO production compared to Con, DS, and P rats despite increased aortic eNOS expression. Aortic superoxide and peroxynitrite levels were increased in PDS rats compared with Con, DS, and P rats. Scavenging of reactive oxygen species or increasing tetrahydrobiopterin levels normalized mesenteric endothelium-dependent relaxation responses, aortic NO production, and aortic superoxide and peroxynitrite levels in PDS rats. CONCLUSIONS: These data suggest that increased superoxide production by NADPH oxidase, peroxynitrite degradation of BH4, and uncoupled eNOS contribute to endothelial dysfunction in a rat model of pregnancy-induced hypertension.     

Regression of L-NAME-induced hypertension: the role of nitric oxide and endothelium-derived constricting factor

N(G)-Nitro-L-arginine-methyl ester (L-NAME)-induced hypertension is a well established model of experimental hypertension. Although regression experiments are effective at approximating a clinical setting the reversal of already established L-NAME hypertension has not been intensively researched. We investigated whether spontaneous regression of L-NAME hypertension after discontinuing the drug administration was associated with recovery of endothelial dysfunction. Special attention was devoted to NO signaling and endothelium-derived constricting factor (EDCF) formation in various parts of the vascular tree. Male adult Wistar rats were divided into 4 groups: an L-NAME (5 weeks), a spontaneous recovery (5 weeks L-NAME + 3 weeks of recovery) and two age-matched control groups (a 5- and 8-week control group). The NO-mediated and EDCF-mediated components of acetylcholine-induced responses were evaluated in preconstricted small mesenteric and femoral arteries. The activity, mRNA and protein expression of NO synthase together with the mRNA expression of cyclooxygenase were determined in the aorta. L-NAME administration caused hypertension, impaired NO signaling (as indicated by the reduced NO component of acetylcholine-induced relaxation and decreased NO synthase activity) in all arteries investigated and reduced the inner diameter of the femoral artery. Moreover, we observed enhanced cyclooxygenase-dependent EDCF formation in the femoral arteries and enhanced cyclooxygenase-2 expression in the aortas of L-NAME-treated rats. During spontaneous recovery a functional restoration of NO signaling took place in all parts of the vascular tree. However, the increases in systolic blood pressure, EDCF formation, and cyclooxygenase expression and the reduction in femoral artery diameter were not completely restored. We conclude that impaired NO signaling was improved after the cessation of L-NAME administration. However, persisting arterial structural alterations and enhanced EDCF formation may decelerate blood pressure reduction even after the restoration of NO synthase activity.     

普罗布考对高脂家兔胸主动脉内皮储备功能的保护作用

为观察口服普罗布考对高胆固醇血症和动脉粥样硬化免主动脉的内皮储备功能的影响,并探讨其可能作用机制。将26只新西兰白兔(体重1.5-2.5 kg)随机分为3组:正常饮食组(普通饮食,n=6)、高脂饮食组(高脂饮食,n=10)、普罗布考治疗组(高脂饮食+普罗布考200mg/kg,n=10)。在高脂饲养前和饲养后第12周,抽血测血清总胆固醇浓度。第12周后处死动物,取胸主动脉,检测离体胸主动脉环对乙酰胆碱与硝普钠的反应。结果发现,①普罗布考有降血脂作用(39.1％);②与正常饮食组相比,高脂血症兔胸主动脉对乙酰胆碱引起的最大的内皮依赖性舒张反应明显降低(0.65±0.14比0.16±0.04,P<0.05),普罗布考能明显保护高胆固醇血症所损伤的内皮依赖性舒张反应(两组最大血管舒张度分别为0.60±0.10比0.16±0.04,P<0.05);③3组对硝普钠所致的非内皮依赖性舒张反应均没有差别。结果提示普罗布考主要是通过降血脂和抗氧化两个途径来保护高脂家兔胸主动脉内皮储备功能。     

Resveratrol lowers blood pressure in spontaneously hypertensive rats via calcium-dependent endothelial NO production

Objective: Resveratrol, a polyphenol of natural compounds, has beneficial cardiovascular effects, many of which are mediated by nitric oxide (NO). Resveratrol increases intracellular calcium and activates AMP-activated protein kinase (AMPK), all of which could increase NO production. We hypothesized that resveratrol via a calcium-dependent NO production lowers blood pressure (BP) in spontaneously hypertensive rats (SHR). Methods: Acetylcholine (Ach)-induced endothelium-dependent relaxations in rat aortas were examined by organ chamber. Blood pressures were determined by radiotelemetry methods. Results: Incubation of isolated aortas from SHR with resveratrol dramatically improved vasorelaxation induced by Ach. Preincubation of aortas with endothelial NO synthase (eNOS) inhibitor or calcium chelant blunted the effects of resveratrol on Ach-induced relaxation, as wells as NO production and eNOS phosphorylation. In animal studies, administration of resveratrol significantly lowered systemic BP in SHR. Conclusion: Resveratrol increases endothelial NO production to improve endothelial dysfunction and lowers BP in hypertensive rats, which depends on calcium-eNOS activation.     

Heterogeneity of endothelium-dependent vasorelaxation in conductance and resistance arteries from Lyon normotensive and hypertensive rats

OBJECTIVES: The nature of endothelial factors in response to acetylcholine (ACh) was investigated in conductance and resistance arteries from Lyon normotensive (LN) and Lyon hypertensive (LH) rats. Differences in endothelial function between the two strains were evaluated. METHODS AND DESIGN: Relaxations to ACh were studied in the aorta and small mesenteric arteries (SMA). The relative contribution of nitric oxide (NO), prostanoids and endothelial-derived hyperpolarizing factor (EDHF) was assessed using appropriate inhibitors. Western blot of endothelial NO synthase was achieved. The membrane potential of smooth muscle cells was assessed using microelectrodes. RESULTS: In LN rats, endothelium-dependent relaxation to ACh involved exclusively NO in the aorta, whereas both NO and EDHF were implicated in SMA. In the latter, relaxation was almost entirely prevented by blockade of either the NO or EDHF pathway, although ACh was still able to produce hyperpolarization in the presence of NO synthase and cyclooxygenase inhibitors. In LH rats, relaxation to ACh was unchanged in SMA but moderately depressed in the aorta, despite unchanged endothelial NO synthase protein expression and sensitivity to NO. In addition, indomethacin, but not a selective cyclooxygenase-2 inhibitor, significantly reduced ACh relaxations in the aorta from LH rats but not from LN rats. CONCLUSIONS: These results document differential endothelial function in a conductance and in resistance arteries from LN rats and LH rats. They show that simultaneous participation of NO and EDHF is required to promote relaxation in SMA from both strains, whereas NO alone accounts for relaxation in aorta from LN rats. In LH rats, aortic relaxation induced by ACh is slightly decreased despite the involvement of vasodilator products from cyclooxygenase-1.     

普罗布考对高脂血症大鼠内皮功能的影响

目的探讨普罗布考对高脂血症大鼠血管内皮功能的影响。方法 50只SD大鼠随机分成5组：对照组（A组）、高脂饲料组（B组）、高脂饲料＋VitD3组（C组）、高脂饲料＋普罗布考组（D组）、高脂饲料＋普罗布考＋VitD3组（E组）。第16周时对大鼠行血流动力学研究,并取血检测血清TG、TC、HDL-C、LDL-C、NO、一氧化氮合酶（NOS）、总抗氧化能力（T-AOC）、丙二醛（MDA）;最后取主动脉制成病理切片,行HE染色。结果与对照组比较,B组TG、TC、LDL-C、NO、NOS水平升高（P均〈0.01）,HDL-C水平降低（P〈0.01）;与未干预组比较,普罗布考干预组NO、NOS、T-AOC水平均升高（P〈0.05）,TC、HDL-C、LDL-C、MDA水平降低（P〈0.05）。血流动力学监测,仅C组大鼠输入硝普钠后血压下降大于输入乙酰胆碱（P〈0.05）。结论普罗布考可以改善动脉粥样硬化大鼠内皮依赖性舒张功能不全。     

Endothelial S100A1 modulates vascular function via nitric oxide

S100A1, a Ca(2+)-binding protein of the EF-hand type, is known to modulate sarcoplasmic reticulum Ca(2+) handling in skeletal muscle and cardiomyocytes. Recently, S100A1 has been shown to be expressed in endothelial cells (ECs). Because intracellular Ca(2+) ([Ca(2+)](i)) transients can be involved in important EC functions and endothelial NO synthase activity, we sought to investigate the impact of endothelial S100A1 on the regulation of endothelial and vascular function. Thoracic aortas from S100A1 knockout mice (SKO) showed significantly reduced relaxation in response to acetylcholine compared with wild-type vessels, whereas direct vessel relaxation using sodium nitroprusside was unaltered. Endothelial dysfunction attributable to the lack of S100A1 expression could also be demonstrated in vivo and translated into hypertension of SKO. Mechanistically, both basal and acetylcholine-induced endothelial NO release of SKO aortas was significantly reduced compared with wild type. Impaired endothelial NO production in SKO could be attributed, at least in part, to diminished agonist-induced [Ca(2+)](i) transients in ECs. Consistently, silencing endothelial S100A1 expression in wild type also reduced [Ca(2+)](i) and NO generation. Moreover, S100A1 overexpression in ECs further increased NO generation that was blocked by the inositol-1,4,5-triphosphate receptor blocker 2-aminoethoxydiphenylborate. Finally, cardiac endothelial S100A1 expression was shown to be downregulated in heart failure in vivo. Collectively, endothelial S100A1 critically modulates vascular function because lack of S100A1 expression leads to decreased [Ca(2+)](i) and endothelial NO release, which contributes, at least partially, to impaired endothelium-dependent vascular relaxation and hypertension in SKO mice. Targeting endothelial S100A1 expression may, therefore, be a novel therapeutic means to improve endothelial function in vascular disease or heart failure.     

Effect of high-salt diet on vascular relaxation and oxidative stress in mesenteric resistance arteries

This study tested the hypothesis that superoxide levels are elevated in isolated mesenteric resistance arteries (100-300 microm) from rats fed a short-term high-salt (HS) diet (4% NaCl for 3 days) compared to controls fed a low-salt (LS) diet (0.4% NaCl). Vascular relaxation induced by the superoxide dismutase mimetic tempol (4-hydroxytetramethylpiperidine-1-oxyl), the NADPH oxidase inhibitor apocynin and the xanthine/xanthine oxidase inhibitor oxypurinol was significantly larger in mesenteric arteries from animals fed HS diet compared to arteries from animals fed LS diet. Basal superoxide levels assessed via dihydroethidine (DHE) fluorescence were significantly elevated in arteries from rats fed HS diet, and were reduced by tempol, apocynin and oxypurinol, but not by L-NAME. Basal and methacholine-induced NO production (assessed by DAF-2T fluorescence) was significantly reduced in arteries from rats fed HS diet versus arteries from rats on LS diet. Impaired methacholine-induced NO release and vascular relaxation were restored by tempol and apocynin, but not by oxypurinol. These data suggest that the elevated production of superoxide by NADPH oxidase and xanthine/xanthine oxidase contribute to elevated basal superoxide levels, reduced NO release and impaired vascular relaxation in mesenteric resistance arteries of rats fed HS diet.     

Mechanism of endothelial dysfunction in apolipoprotein E-deficient mice

Endothelium-dependent relaxations mediated by NO are impaired in a mouse model of human atherosclerosis. Our objective was to characterize the mechanisms underlying endothelial dysfunction in aortas of apolipoprotein E (apoE)-deficient mice, treated for 26 to 29 weeks with a lipid-rich Western-type diet. Aortic rings from apoE-deficient mice showed impaired endothelium-dependent relaxations to acetylcholine (10(-)(9) to 10(-)(5) mol/L) and Ca(2+) ionophore (10(-)(9) to 10(-)(6) mol/L) and endothelium-independent relaxations to diethylammonium (Z)-1-(N,N-diethylamino)diazen-1-ium-1,2-diolate (DEA-NONOate, 10(-)(10) to 10(-)(5) mol/L) compared with aortic rings from C57BL/6J mice (P<0.05). By use of confocal microscopy of an oxidative fluorescent probe (dihydroethidium), increased superoxide anion (O(2)(-)) production was demonstrated throughout the aortic wall but mainly in smooth muscle cells of apoE-deficient mice. CuZn-superoxide dismutase (SOD) and Mn-SOD protein expressions were unaltered in the aorta exposed to hypercholesterolemia. A cell-permeable SOD mimetic, Mn(III) tetra(4-benzoic acid) porphyrin chloride (10(-)(5) mol/L), reduced O(2)(-) production and partially normalized relaxations to acetylcholine and DEA-NONOate in apoE-deficient mice (P<0.05). [(14)C]L-Citrulline assay showed a decrease of Ca(2+)-dependent NOS activity in aortas from apoE-deficient mice compared with C57BL/6J mice (P<0.05), whereas NO synthase protein expression was unchanged. In addition, cGMP levels were significantly reduced in the aortas of apoE-deficient mice (P<0.05). Our results demonstrate that in apoE-deficient mice on a Western-type fat diet, impairment of endothelial function is caused by increased production of O(2)(-) and reduced endothelial NO synthase enzyme activity. Thus, chemical inactivation of NO with O(2)(-) and reduced biosynthesis of NO are key mechanisms responsible for endothelial dysfunction in aortas of atherosclerotic apoE-deficient mice.     

A lipoprotein lipase activator,NO-1886 prevents impaired endothelium-dependent relaxation of aorta caused by exercise in aged rats

Exercise decreases plasma total cholesterol and triglycerides, and simultaneously, increases high density lipoprotein (HDL) cholesterol. As a result, exercise is believed to aid in preventing atherosclerosis. However, we do not know whether exercise protects against the development of atherosclerosis in the elderly. The aim of this study was to ascertain whether the lipoprotein lipase activator NO-1886 had an effect on the prevention of atherosclerosis in aged rats which undergo exercise. Exercise for 3 months did not affect plasma lipids but decreased the accumulation of visceral fat in 2-year-old rats (aged rat). Exercise also resulted in an elevation of plasma lipid peroxide (LPO) levels and impaired the endothelium-dependent relaxation of the thoracic aorta caused by acetylcholine in aged rats. On the other hand, NO-1886 decreased plasma triglycerides and increased HDL cholesterol and suppressed the elevation of plasma LPO levels caused by exercise. Furthermore, NO-1886 prevented impaired endothelium-dependent relaxation caused by exercise. In summary, the results of our study indicate that exercise may cause impaired endothelium-dependent relaxation by elevation of LPO in aged rats, and that NO-1886 prevents this impaired endothelium-dependent relaxation of aorta by reducing plasma triglycerides, elevating HDL cholesterol, and suppressing the elevation of plasma LPO caused by exercise.