Oxidized LDL from subjects with different dietary habits modifies atherogenic processes in endothelial and smooth muscle cells

Low-density lipoprotein (LDL) activates a number of processes involved in atherogenesis and vasoconstriction. Evidence suggests that oxidation increases the atherogenicity of LDL. We investigated the effects of oxidized LDL (ox-LDL) on cytotoxicity, prostacyclin (PGI2), and cyclic guanosine-3',5'-monophosphate (cGMP) production in rat vascular smooth muscle cell (VSMC) and rat heart endothelial cell (EC) culture, as well as EC- and VSMC-mediated LDL oxidation. Native LDL (n-LDL) was isolated from subjects on three long-term diets with differing fatty acid content (control diet rich in saturated fat and vegetarian and fish diets). The Cu2+-catalyzed oxidation of n-LDL was monitored using conjugated diene formation and stopped at various time points to achieve 20%, 45%, 70%, and 100% levels of ox-LDL. The lag phase of oxidation by Cu2+ was shortest and thiobarbituric acid-reactive substance (TBARS) formation by VSMC-mediated oxidation was highest with n-LDL obtained from the fish diet group. There were no differences between the ox-LDLs obtained from the different diet groups in their cytotoxicity in EC culture. The degree of oxidation did not influence LDL cytotoxicity. In VSMC culture PGI2 production was increased by ox-LDLs from all diet groups. In EC culture only the extensively oxidized LDLs obtained from the vegetarian diet group were able to induce PGI2 production. The LDLs did not affect basal cGMP production in either EC or VSMC culture.     

长期高饱和、高不饱和脂肪酸饮食诱导胰岛素抵抗大鼠肾动脉舒张和收缩功能的变化

本文旨在探讨长期高饱和、高不饱和脂肪酸饮食诱导胰岛素抵抗（insulin resistance,IR）大鼠。肾动脉舒张和收缩功能的变化。成年Wistar大鼠随机分为对照组、高饱和脂肪酸组和高不饱和脂肪酸组,每组14只。喂养6个月后,用高胰岛素正常葡萄糖钳夹技术的葡萄糖输注率（glucose infusion rate,GIR）评价IR;用尾套法测定大鼠血压,同时比较三组大鼠的体重、血清甘油三酯、游离脂肪酸、胰岛素、空腹血糖和NO代谢产物NO2-／NO3-。大鼠处死后,取肾动脉放入生理盐溶液中,观察血管对各种因子的舒、缩反应。结果显示,喂养6个月后,与对照组大鼠比较,高饱和脂肪酸组和高不饱和脂肪酸组大鼠均出现血压升高、血清甘油三酯升高和胰岛素敏感性降低;体重、空腹血糖、胰岛素和游离脂肪酸均升高（P〈0．01）：而两高脂组间体重、空腹血糖、胰岛素和游离脂肪酸无显著性差异。高饱和脂肪酸组大鼠肾动脉对ACh的内皮依赖性最大舒张反应（Rmax）最低,其次为高不饱和脂肪酸组和对照组：对照组与两高脂组有显著性差异（P〈0．01）,而两高脂组间无显著性差异。血管经L-Arg孵育后,两高脂组肾动脉对ACh的内皮依赖性Rmax均比孵育前增加,经N^ω-吐硝基-L-精氨酸（N^ω-nitro-L-arginine,L-NNA）及美蓝（methyleneblue,MB）孵育后,两高脂组Rmax均比孵育前降低（P〈0．05,P〈0．01）;对照组各孵育液之间无显著性差异（P：〈0．05）。肾动脉对硝普钠的非内皮依赖性Rmax及对去甲肾上腺素的收缩反应,三组间无显著性差异（P〈0．05）。相关分析结果显示,肾动脉对ACh的内皮依赖性Rmax与收缩压、甘油三酯呈明显负相关,与NO2-／NO3-和GIR呈明显正相关,游离脂肪酸与N02-／NO3-呈明显负相关。结果提示,高饱和及高不饱和脂肪酸饮食均可引起高血压及与之密切相关的内皮依赖性血管舒张功能减弱、高脂血症和IR,高脂诱导内皮依赖性血管舒张功能减弱与L-Arg-NO-cGMP通路受损有关。     

Dietary fatty acids and oxidative stress in the heart mitochondria

Our study compared the effects of different oils on oxidative stress in rat heart mitochondria, as well as on plasma parameters used as risk factors for cardiovascular disease. The rats were fed for 16 weeks with coconut, olive, or fish oil diet (saturated, monounsaturated, or polyunsaturated fatty acids, respectively). The cardiac mitochondria from rats fed with coconut oil showed the lowest concentration of oxidized proteins and peroxidized lipids. The fish oil diet leads to the highest oxidative stress in cardiac mitochondria, an effect that could be partly prevented by the antioxidant probucol. Total and LDL cholesterols decreased in plasma of rats fed fish oil, compared to olive and coconut oils fed rats. A diet enriched in saturated fatty acids offers strong advantages for the protection against oxidative stress in heart mitochondria.     

Inhibitory effects of melatonin on vascular reactivity: possible role of vasoactive mediators

Melatonin (MEL), the principal hormone of the vertebral pineal gland, elicits several neurobiological effects. However, the effects of MEL on vascular tissues are still vague. The first goal of this study was to investigate the effect of MEL on isolated rabbit aortic rings and its role in the vascular reactivity to contractile agents, noradrenaline (NA) and phenylephrine (PHE) and relaxant agents (acetylcholine and sodium nitroprusside). In addition, the levels of nitric oxide (NO), cGMP, total calcium, lipid peroxides, superoxide dismutase (SOD) and glutathione (GSH) were also investigated in tissue homogenates of rabbit aortic rings preincubated (20 min) in MEL with and without contractile agents. Our results revealed that MEL has an endothelium-dependent vaso-relaxant effect and potentiated significantly the vaso-relaxant effect of acetylcholine. Moreover, MEL (10^?4 M) had a significant inhibitory effect on the contractile responses of aortic rings to both NA and PHE. In comparison with control tissue rings, the levels of lipid peroxides were significantly increased while the levels of GSH, and SOD activities were significantly decreased in tissue homogenates of aortic rings pre-incubated (20 min) in NA or PHE. In addition, the levels of NO and cGMP were significantly lower in tissue rings pre-treated with NA and PHE, respectively. Also, the levels of total calcium were significantly increased only in tissue rings pre-treated with NA. The levels of lipid peroxides were significantly decreased, while the levels of GSH, NO and cGMP and SOD activities were significantly increased in tissue homogenates of aortic rings incubated (20 min) in MEL (10^?4 M) in comparison to ring tissues incubated in NA or PHE alone. In aortic rings incubated in MEL+PHE, the levels of lipid peroxides were significantly lower while the levels of GSH and cGMP and SOD activities were significantly higher than their levels in ring tissues incubated in PHE. In aortic rings incubated in MEL+NA, the levels of lipid peroxides and total calcium were significantly lower while the levels of NO were significantly higher than their levels in ring tissues incubated in NA alone. We conclude that MEL has an endothelium dependent vasorelaxant effect and potentiates the endothelium dependent vasorelaxation induced by acetylcholine. MEL inhibits the contractile responses of aortic rings to NA and PHE. These effects may be, in part, due to re-balancing the pro-oxidant/antioxidants system, lowered calcium content and elevated NO and cGMP levels in vascular tissue.     

Dietary n-3 fatty acids alter the contractile response to thromboxane A(2) agonists of porcine coronary arteries

Dietary supplementation with marine fish oils rich in n-3 fatty acids reduces circulating thromboxane A(2) (TxA(2)). However, the effects on thomboxane A(2) receptor mediated vascular reactivity are uncertain. The aim of this study was to test the hypothesis that dietary modification of TxA(2) levels alters vascular responsiveness to TxA(2) analogues. Juvenile female white pigs were fed a diet enriched in either 5% (w/w) fish oil or beef tallow for 6 weeks. Serum and myocardial tissue levels of eicosapentaenoic and docosahexaenoic acid reached a plateau during this period. Vascular responses were measured in isolated coronary arterial rings with intact endothelium by isometric tension measurement. Arteries from pigs fed fish oil produced a greater maximum vasoconstrictor tension to the TxA(2) analogue U46619 than did rings from pigs fed beef tallow (120 +/- 6% compared to 92 +/- 8%, values represented as a percentage relative to the maximum vasoconstrictor effect obtained to KCl, regression analysis, analysis of variance, P 相似文献   

Effect of fish oil and coconut oil diet on the LDL receptor activity of rat liver plasma membranes

The influence of 4 weeks treatment with fish oil and coconut oil enriched diets on the chemical composition of rat liver plasma membranes and LDL and on the binding of LDL to liver membranes was investigated. Rats fed fish oil diet showed a total, LDL and HDL plasma cholesterol concentration lower than the values observed in rats fed coconut oil and to a lesser extent lower than those of rats fed standard laboratory diet. LDL of rats on fish oil diet had a relative percentage of cholesterol and phospholipid lower, while that of triacylglycerol was greater. Furthermore, fish oil feeding was associated with a greater concentration of n - 3 fatty acids and a lower arachidonic and linoleic acid content in LDL. Liver plasma membranes isolated from fish oil rats showed a higher percentage of n - 3 fatty acids, while only a trace amount of these fatty acids was found in control and coconut oil fed animals. In binding experiments performed with LDL and liver membranes from fish oil fed rats and control rats, binding affinity (Kd = 3.47 +/- 0.93 and 4.56 +/- 1.27, respectively) was significantly higher (P less than 0.05) as compared to that found using membranes and lipoprotein from coconut oil fed rats (Kd = 6.82 +/- 2.69). In cross-binding experiments performed with fish oil LDL and coconut oil liver plasma membranes or coconut oil LDL and fish oil liver plasma membranes, the LDL binding affinity was comparable and similar to that found in fish oil fed animals. No difference was found in the Bmax among all the groups of binding experiments. Our data seem to indicate that during fish oil diet the higher binding affinity of LDL to liver plasma membranes might be partly responsible of the hypocholesterolemic action of marine oil rich diet as compared to saturated diet. Furthermore, the modifications of binding affinity induced by changes of LDL and membrane source, suggest that lipoprotein and liver plasma membrane composition may be an important variable in binding studies.     

Nitric oxide pathway counteracts enhanced contraction to membrane depolarization in aortic rings of rats on high-sodium diet

Vascular smooth muscle cell contraction and endothelium-dependent relaxation was evaluated in aortic rings isolated from weaned, 5-mo-old Sprague-Dawley rats fed a normal (NS; 0.8% NaCl) or high (HS; 8% NaCl) sodium diet. Arterial pressure was 140 +/- 6 (NS) and 145 +/- 6 mmHg (HS). In endothelium-denuded rings, the response to phenylephrine (PE) was not modified by the sodium diet, while that of depolarizing agent KCl and intracellular calcium releasing agent caffeine increased in the HS group. When endothelium was preserved, PE-evoked contraction was reduced in both NS and HS groups, the contraction being yet lower in the HS group. This effect was partially obliterated by addition of N(G)-nitro-L-arginine methyl ester (L-NAME), independently of the sodium diet. Relaxation to ACh in intact rings and to sodium nitroprusside (SNP) and 8-bromoadenosine 3'5' cyclic guanosine monophosphate (8-BrcGMP) in the absence of endothelium was enhanced in rings isolated from HS rats. In addition, the dose-response curve to 8-BrcGMP was shifted to the right in the presence of iberiotoxin, an inhibitor of large conductance, voltage-dependent, and calcium-sensitive potassium channel (BK(Ca)). However, shift was more marked in rings from HS rats. Present results provide evidence that response of vascular smooth muscle cell to nitric oxide/cGMP-related compounds is increased in HS rings and is associated with a greater activation of the repolarizing BK(Ca) channels. Such changes might counterbalance enhanced contractile response to membrane depolarization and thus participate in maintenance of arterial pressure in the present model of early and long-term HS feeding in rats.     

EFFECTS OF DIETARY Spirulina maxima ON ENDOTHELIUM DEPENDENT VASOMOTOR RESPONSES OF RAT AORTIC RINGS

The aim of this study was to evaluate the effects of Spirulina maxima on vasomotor responses of aorta rings from male Wistar rats fed on a purified diet. For this purpose, the animals (weighing 200–240 g) were allocated randomly in two groups. One receiving purified control diet (A) and the other receiving purified diet containing 5% Spirulina (B). Purified diets were according to American Institute of Nutrition guidelines and adjusted to Spirulina protein content. All animals were fed (20 g/day/rat) during two weeks, receiving water ad libitum and 12 h. lightdark cycles. Spirulina maxima effects were evaluated by concentration-response (CR) curves of aorta rings with or without endothelium to phenylephrine (PE), both in presence and absence of indomethacin (Indom) or indomethacin plus L-NAME (Indom. + L-NAME), and to carbachol (CCh). Aorta rings with endothelium from group B showed, relative to corresponding rings from group A: 1) a significant decrease in the maximal tension developed in response to PE. 2) this decrease was reverted by Indom. 3) Indom. + L-NAME induced an additional increase in the contractile responses to PE. 4) a significant shift to the left of the CR curve to CCh. No significant differences were observed in the tension developed in response to PE in rings without endothelium from either group. These results suggest that Spirulina maxima may decrease vascular tone by increasing the synthesis and release of both a vasodilating cyclooxygenase-dependent product of arachidonic acid and nitric oxide, as well as by decreasing the synthesis and release of a vasoconstricting eicosanoid from the endothelial cells. © 1997 Elsevier Science Inc.     

Simulated microgravity enhances vasoconstrictor responsiveness of rat basilar artery.

Recently, hypertrophy and increased myogenic tone of brain vessels have been observed in rats after simulated microgravity. It is expected that simulated microgravity may also induce hyperreactivity of brain vessels. To test this hypothesis, Sprague-Dawley rats were subjected to a 4-wk tail-suspended hindlimb unloading (TS) to simulate the cardiovascular deconditioning effect of microgravity. After 4 wk, the vasoreactivity of isolated basilar arterial rings from TS rats to both receptor- and non-receptor-mediated vasoconstrictors, such as KCl, arginine vasopressin, or 5-hydroxytryptamine (5-HT), and vasodilators such as ACh, thrombin, adenosine, or sodium nitroprusside were examined and compared with those from simultaneous control (Cn) rats. In the first part of this study, it was found that the maximal isometric contractile responsiveness evoked by vasoconstrictors such as KCl, arginine vasopressin, or 5-HT was enhanced in basilar arterial rings from TS rats, whereas vasodilatory responsiveness to vasodilators showed no significant difference between TS and Cn rats. In the second part of this study, it was found that removal of the endothelium had no effects on the contractile responsiveness to 5-HT in basilar arterial rings from TS rats but enhanced markedly the responsiveness in basilar arterial rings from Cn rats to an extent comparable with that of TS rats. Application of tetraethylammonium also had no effects on the contractile response to 5-HT in basilar arterial rings from TS but significantly increased the responsiveness of basilar arterial rings from Cn rats with endothelium intact. These results showed that 4-wk simulated microgravity enhanced the vascular contractile responsiveness of basilar arterial rings to both receptor- and non-receptor-mediated vasoconstrictors, and the enhancement of 5-HT-induced contraction in TS rat basilar arteries was due to an impairment of endothelium-dependent mechanism. These results suggest that endothelium-derived hyperpolarizing factors are responsible for this endothelium-dependent attenuating modulatory mechanism in contractile responsiveness of rat basilar arteries to 5-HT.     

Platelet factor 4 enhances the binding of oxidized low-density lipoprotein to vascular wall cells

Accumulation of low-density lipoprotein (LDL)-derived cholesterol by macrophages in vessel walls is a pathogenomic feature of atherosclerotic lesions. Platelets contribute to lipid uptake by macrophages through mechanisms that are only partially understood. We have previously shown that platelet factor 4 (PF4) inhibits the binding and degradation of LDL through its receptor, a process that could promote the formation of oxidized LDL (ox-LDL). We have now characterized the effect of PF4 on the binding of ox-LDL to vascular cells and macrophages and on the accumulation of cholesterol esters. PF4 bound to ox-LDL directly and also increased ox-LDL binding to vascular cells and macrophages. PF4 did not stimulate ox-LDL binding to cells that do not synthesize glycosaminoglycans or after enzymatic cleavage of cell surface heparan and chondroitin sulfates. The effect of PF4 on binding ox-LDL was dependent on specific lysine residues in its C terminus. Addition of PF4 also caused an approximately 10-fold increase in the amount of ox-LDL esterified by macrophages. Furthermore, PF4 and ox-LDL co-localize in atherosclerotic lesion, especially in macrophage-derived foam cells. These observations offer a potential mechanism by which platelet activation at sites of vascular injury may promote the accumulation of deleterious lipoproteins and offer a new focus for pharmacological intervention in the development of atherosclerosis.     

肺纤维化初期肺动脉高压大鼠肺动脉反应性的变化

目的：观察肺纤维化初期肺动脉高压大鼠肺动脉血管反应性的变化。方法：66只雄性SD大鼠,随机分为博莱霉素（BLM）组和手术对照（Sham）组。BLM组为气管内一次性滴注BLM（5 mg/kg）;Sham组为气管内滴注等容量的生理盐水（NS）。应用离体血管张力检测技术测定大鼠肺动脉血管反应性变化;用HE显示肺动脉壁病理形态学变化;Masson染色检测肺纤维化程度;右心漂浮导管技术测定大鼠平均肺动脉压。结果：①BLM组大鼠的肺动脉血管（保留内皮和去内皮）对苯肾上腺素（PE）的收缩反应均弱于Sham组（P均〈0.05）。②BLM组大鼠肺动脉血管（保留内皮）对氯化乙酰胆碱（Ach）的舒张反应明显弱于Sham组（P〈0.01）。③Sham组有内皮的肺动脉血管对L-NAME和PE联合作用的收缩反应明显强于PE单独作用（P〈0.01）,而BLM组有内皮肺动脉血管对L-NAME和PE联合作用的收缩反应与对PE单独作用比,其差异无统计学意义（P〉0.05）。④BLM组肺动脉内皮细胞脱落。⑤BLM组大鼠肺组织呈现纤维增生初期的病理特征,且大鼠的平均肺动脉压明显高于Sham组（P〈0.05）。结论：肺纤维化形成初期肺动脉高压大鼠肺动脉血管反应性出现异常。     

Interaction of dietary saturated and polyunsaturated triglycerides in regulating the processes that determine plasma low density lipoprotein concentrations in the rat

These studies were undertaken to determine how polyunsaturated (n-3 and n-6) and saturated triglycerides interact to regulate rates of low density lipoprotein (LDL) production and rates of receptor-dependent and receptor-independent LDL transport. Animals were fed diets containing 20% (by wt) hydrogenated coconut oil or diets in which the coconut oil was progressively removed and replaced with safflower oil or fish oil concentrate. Plasma LDL concentrations fell when either of the polyunsaturated triglycerides was substituted for saturated triglycleride in the diet; however, the reduction in LDL concentrations was greater with fish oil than with safflower oil at all ratios of polyunsaturated to saturated triglyceride that were examined. The lower plasma LDL concentrations when coconut oil was replaced with fish oil could be attributed almost entirely to a much greater increase in hepatic LDL receptor activity when fish oil was used as the substitute than when safflower oil was used as the substitute. To examine the effect of polyunsaturated triglycerides when used to supplement a high saturated fat diet rather than to replace saturated fat in the diet, animals were fed a diet containing 15% coconut oil (by wt) with or without an additional supplement of 5% fish oil or safflower oil. The addition of 15% coconut oil to low fat control diet increased the rate of LDL production causing circulating LDL levels to rise by 40%. The further supplementation of this high saturated fat diet with fish oil concentrate markedly increased hepatic LDL receptor activity causing plasma LDL concentrations to return to control values whereas supplementation with safflower oil had little effect. Thus, at least in the rat, supplementation of a high saturated fat diet with a fish oil concentrate lowers plasma LDL concentrations as effectively as removing the saturated fat from the diet, although in the former case, both the production and the receptor-dependent uptake of LDL are greatly increased.     

Vascular smooth muscle-derived relaxing factor (MDRF) and its close similarity to nitric oxide

The principal finding in this study is that vascular smooth muscle generates a labile relaxing factor that possesses pharmacological and chemical properties that are similar to those of authentic nitric oxide. MDRF was generated by perfusion of endothelium-denuded bovine pulmonary artery as assessed by bioassay. In addition, endothelium-denuded arterial rings that were incubated at 37 degrees C for 24 hr to lower endogenous L-arginine levels relaxed in response to L-arginine but not D-arginine. Freshly mounted, endothelium-denuded arterial rings were not relaxed by L-arginine but did relax in response to the dipeptide L-arginyl-L-alanine. Relaxant responses were accompanied by increases in smooth muscle levels of cyclic GMP and nitrite, and were inhibited by oxyhemoglobin, methylene blue, and NG-nitro-L-arginine. NG-Nitro-L-arginine also caused endothelium-independent contractile responses. Thus, a relaxing factor with the properties of nitric oxide can be generated from vascular smooth muscle.     

Inhibitory effect of manganese on contraction of isolated rat aorta

The effects of MnCl2 on vascular smooth muscle contraction induced by noradrenaline (NA) and KCl were investigated. Rings segments from rat aorta were isolated and changes in isometric tension recorded. MnCl2 (10 microM and 1 mM) significantly attenuated the contractile responses to NA and KCI. There were also reductions in the contractile responses to CaCl2 in NA- and KCl-stimulated rings, after pretreatment with MnCl2. The magnitude of the phasic contraction to NA was significantly reduced in presence of MnCl2. The results suggest that MnCl2 inhibits vascular smooth muscle contraction by influencing a Ca2+-mediated mechanism.     

The autophagy-lysosome pathway: A novel mechanism involved in the processing of oxidized LDL in human vascular endothelial cells

Oxidized low-density lipoprotein (ox-LDL) is involved in the pathogenesis of atherosclerosis and atherosclerotic plaque rupture by promoting lipid accumulation, proinflammatory responses, and cell death. LDL is mainly oxidized in the subendothelial layer of the vascular wall and then can be taken up by vascular endothelial cells. However, little is known about the intracellular processing of the damaged LDL. Previous studies found that autophagy is involved in degrading oxidized proteins under oxidative stress conditions in Arabidopsis thaliana, while ox-LDL can activate autophagy in EA.hy926 endothelial cells, suggesting a possible role of autophagy in the degradation of ox-LDL by endothelial cells. The present study showed that ox-LDL aggregated in human umbilical vein endothelial cells (HUVECs) and brought about an increase in the formation of autophagosomes and autolysosomes. Ox-LDL-induced increase in the autophagic level was blocked by treatment with the autophagy inhibitor 3-methyladenine and increased by the autophagy inducer rapamycin, while the aggregation of Dil-labled ox-LDL was increased by 3-methyladenine and decreased by rapamycin. In addition, Dil-labeled ox-LDL colocalized with the autophagy marker MDC, microtubule-associated protein light chain 3 (MAP1-LC3), and lysosome-associated membrane protein 2a (lamp2a). HUVECs treated with Dil-labeled-ox-LDL showed a much greater degree of overlap of MAP1-LC3 and Lamp2a than control. The results suggest that ox-LDL activates the autophagic lysosome pathway in HUVECs through the LC3/beclin1 pathway, leading to the degradation of ox-LDL.     

Vascular reactivity and high dietary eicosapentaenoic acid

Epidemiologic studies suggest that high dietary intake of eicosapentaenoic acid (EPA), a precursor of the trienoic prostaglandins, is associated with a low incidence and reduced extent of myocardial infarction. Vascular reactivity of isolated aortic strips from rats maintained for 3 weeks on a control diet or on a diet supplemented with menhaden fish oil (17% EPA) was examined with norepinephrine, sodium arachidonate, KC1, PGF2 alpha and nitroprusside. Aortic strips from rats fed the fish oil diet were significantly less responsive to the contractile effects of norepinephrine and arachidonate compared to those from control diet rats. Treatment of aortic strips with indomethacin decreased responsiveness to norepinephrine. The magnitude of the decrease was greater in control rats resulting in a similar vascular response between the 2 groups after blockade. Contractions to arachidonate were abolished by indomethacin. There were no differences in vascular responses to KC1, PGF2 alpha and nitroprusside in aortic strips from control diet rats and those from the fish oil diet rats. Aortic strips from the fish oil diet rats contained more EPA than those from the control diet rats. Thus, the contractile effect of norepinephrine in isolated rat aortic strips is normally augmented by intrinsic prostaglandins, and this augmentation is diminished by dietary intake of EPA.     

Combined effects of niacin and chromium treatment on vascular endothelial dysfunction in hyperlipidemic rats

Combined treatment with niacin and chromium has been found to have a protective effect against oxidative damage to different tissues of hyperlipidemic rats. But its effects on vascular endothelial dysfunction are less clear. This study was performed to investigate the effect of combined treatment with niacin and chromium on vascular endothelial dysfunction, with the aim of gaining insight to the mechanisms by detecting the expression levels of ox-LDL and LOX-1. Twenty-four male, 4-week-old Wistar rats were randomly divided into three groups: control group (CG; n = 8), high-fat group (HF; n = 8), and drug control group (DG; n = 8).In CG group, rats were fed with pellet chow. In HF group, rats were fed with high-fat diet for 12 weeks. In DG group, rats were fed with the same high-fat diet and treated with CrCl₃ · 6H₂O (250 μg/kg days) and niacin (100 mg/kg days) by gavage technique for 12 weeks. At the end of the 12th week, samples from aorta and blood were collected. In HF group, the serum levels of total cholesterol (TC), low-density lipoprotein (LDL), oxidized low-density lipoprotein (ox-LDL) and endothelin (ET) were higher, whereas the levels of high-density lipoprotein (HDL), serum NO were lower than those in CG group. The levels of serum TC, LDL, ox-LDL and ET decreased and HDL, NO levels increased in DG group when compared with HF group. The levels of LOX-1, ICAM-1 were also observed in abdominal artery. In HF group, the protein and mRNA expression of LOX-1, ICAM-1 were elevated comparing with CG group. In DG group, the protein and mRNA expression of LOX-1, ICAM-1 were decreased obviously, but still differed significantly from those in CG group. ox-LDL was related positively to TC, LDL, ET, ICAM-1 and LOX-1, but related negatively to NO and HDL. These findings indicated that combined treatment with niacin and chromium has potential therapeutic protection of endothelial function by down-regulating ox-LDL/LOX-1 signaling pathway.     

Decreased pulmonary vascular responsiveness in rats raised on an essential fatty acid deficient diet

Leukotriene C4 is produced during hypoxic pulmonary vasoconstriction and leukotriene inhibitors preferentially inhibit the hypoxic pressor response in rats. If lipoxygenase products are important in hypoxic vasoconstriction, then an animal deficient in arachidonic acid should have a blunted hypoxic pressor response. We investigated if vascular responsiveness was decreased in vascular rings and isolated perfused lungs from rats raised on an essential fatty acid deficient diet (EFAD) compared to rats raised on a normal diet. Rats raised on the EFAD diet had decreased esterified plasma arachidonic acid and increased 5-, 8-, 11-eicosatrienoic acid compared to rats raised on the normal diet (control). Compared to the time matched responses in control isolated perfused lungs the pressor responses to angiotensin II and alveolar hypoxia were blunted in lungs from the arachidonate deficient rats. This decreased pulmonary vascular responsiveness was not affected by the addition of indomethacin or arachidonic acid to the lung perfusate. Similarly, the pulmonary artery rings from arachidonate deficient rats demonstrated decreased reactivity to norepinephrine compared to rings from control rats. In contrast, the tension increases to norepinephrine were greater in aortic rings from the arachidonate deficient rats compared to control. Stimulated lung tissue from the arachidonate deficient animals produced less slow reacting substance and platelet activating factor like material but the same amount of 6-keto-PGF1 alpha and TXB2 compared to control lungs. Thus there is an association between altered vascular responsiveness and impairment of stimulated production of slow reacting substance and platelet activating factor like material in rats raised on an EFAD diet.     

Vascular reactivity and high dietary eicopentaenoic acid

Epidemiologic studies suggest that high dietary intake of eicosapentaenoic acid (EPA), a precursor of the trienoic prostaglandins, is associated with a low incidence and reduced extent of myocardial infarction. Vascular reactivity of isolated aortic strips from rats maintained for 3 weeks on a control diet or on a diet supplemented with menhaden fish oil (17% EPA) was examined with norepinephrine, sodium arachidonate, KCl, PGF₂α and nitroprusside. Aortic strips from rats fed the fish oil diet were significantly less responsive to the contractile effects of norepinephrine and arachidonate compared to those from control diet rats. Treatment of aortic strips with indomethacin decreased responsiveness to norepinephrine. The magnitude of the decrease was greater in control rats resulting in a similar vascular response between the 2 groups after blockade. Contractions to arachidonate were abolished by indomethacin. There were no differences in vascular responses to KCl, PGF₂α and nitroprusside in aortic strips from control diet rats and those from the fish oil diet rats. Aortic strips from the fish oil diet rats contained more EPA than those from the control diet rats. Thus, the contractile effect of norepinephrine in isolated rat aortic strips is normally augmented by intrinsic prostaglandins, and this augmentation is diminished by dietary intake of EPA.     

High Glucose-enhanced Acetylcholine Stimulated CGMP Masks Impaired Vascular Reactivity in Tail Arteries from Short-Term Hyperglycemic Rats

Impaired vascular endothelium-dependent relaxation and augmented contractile responses have been reported in several models of long-term hyperglycemia. However, the effects of short-term ambient hyperglycemia are poorly understood. Since oxidative stress has been implicated as a contributor to impaired vascular function, we investigated the following:Aims: (1) the effects of high glucose exposure in vitro (7 – 10 days) on vascular relaxation to acetylcholine (Ach) and contractility to norepinephrine (NE) and KCl; (2) if NO-dependent cGMP generation is affected under these conditions; and (3) aortic redox status.Methods: Non-diabetic rat tail artery rings were incubated in normal (5mM) (control NG) or high (20mM) glucose buffer (control HG). Vascular responses to Ach, NE and KCl were compared to those of streptozotocin (SZ) diabetic animals in the same buffers (diabetic NG, diabetic HG). Ach stimulated cGMP levels were quantitated as an indirect assessment of endothelial nitric oxide (NO) production and oxidative stress evaluated by measuring vascular glutathione and oxidized glutathione.Results: Rings from diabetic rats in NG showed impaired relaxation to Ach (P = 0.002) but relaxed normally, when maintained in HG. Similarly, contractile responses to NE were attenuated in diabetic rings in NG but similar to controls in HG. HG markedly augmented maximal contraction to KCl compared to control and diabetic vessels in NG (P < 0.0001). Diabetic vessels in a hyperosmolar, but normoglycemic, milieu respond like those in HG. in vitro, HG for 2 hours changed neither relaxation nor contractile responses to NE and KCl in control rings. Basal cGMP levels were lower in aortae from diabetic animals pre-incubated in NG than in HG/LG or in control rings in NG (P < 0.05). cGMP responses to Ach were exaggerated in diabetic vessels in HG (P = 0.035 vs. control NG, P = 0.043 vs. diabetic NG) but not different between control and diabetic rings in NG. Vessels from diabetic animals had lower levels of GISH (P < 0.0001) and higher levels of GSSG (P < 0.0001) indicating oxidative stress.Conclusions: Our data indicate that endothelium dependent relaxation is altered early in the diabetic state and that increased NO responses may compensate for augmented oxidative stress but the lack of effect of short-term exposure of normal vessels to HG suggests that short-term hyperglycemia per se does not cause abnormal vascular responses.