Persistent impairment of endothelium-dependent relaxation to acetylcholine and progression of atherosclerosis following 6 weeks of cholesterol feeding in the rabbit

The synthesis and (or) release of endothelium-dependent relaxant factor released by acetylcholine is impaired in New Zealand white rabbits fed an atherogenic diet. Experiments were designed to investigate whether the synthesis and (or) release of the endothelium-dependent relaxant factor from rabbit aortas are restored after reversal from an atherogenic diet to a non-atherogenic diet. Atherosclerosis was induced by feeding a diet containing lipids and 2% cholesterol for 6 weeks. Rabbits were sacrificed after 6 weeks on the atherogenic diet and 36 weeks after return to a standard laboratory diet. Synthesis and (or) release of the factor from the thoracic aorta was assayed using a bioassay system. The relaxant responses produced in the assay tissue were impaired both in the acute stage and after 36 weeks on non-atherogenic food. This impaired relaxation is probably due to a persistent functional abnormality in the aortic endothelium resulting in the failure to synthesize and (or) release endothelium-dependent relaxation factor 36 weeks after induction of atherosclerosis.     

A model for demonstration of reversal of impairment of endothelium-dependent relaxation in the cholesterol-fed rabbit.

This investigation was undertaken to determine whether it was possible to restore endothelium-dependent relaxation (EDR) in the cholesterol-fed rabbit model of atherosclerosis following discontinuation of the cholesterol. New Zealand white rabbits, approximately 8 weeks of age, were randomized into (i) control group (9 animals fed a standard rabbit diet) and (ii) experimental group (27 animals: fed the same diet supplemented with 2.5% cholesterol). The experimental animals were restored to the standard diet after 3 weeks. EDR to acetylcholine (-9.0 to -5.0 log mol/L) was examined in the experimental animals at 3, 7, and 15 weeks after commencement of the study (n = 9 at each stage) and the nine control animals examined after 7 weeks. At the end of 7 weeks, EDR to acetylcholine (-6.0 log mol/L) was significantly (p less than 0.05) impaired in the experimental group (34.3 +/- 3.8%) compared with that in the control group (79.8 +/- 3.0%). The loss of EDR was not apparent in the experimental group at 3 weeks (relaxation: 81.7 +/- 4.7%). At the end of 15 weeks, the EDR was significantly restored in the experimental group (relaxation: 63.6 +/- 5.1%). These findings demonstrate that it is possible to reverse the loss of EDR that occurs with cholesterol feeding in the rabbit by limiting the period of exposure to a high cholesterol diet.     

Effects of dietary flaxseed on vascular contractile function and atherosclerosis during prolonged hypercholesterolemia in rabbits

Dietary flaxseed has significant anti-atherogenic effects. However, the limits of this action and its effects on vascular contractile function are not known. We evaluated the effects of flaxseed supplementation on atherosclerosis and vascular function under prolonged hypercholesterolemic conditions in New Zealand White rabbits assigned to one of four groups for 6, 8, or 16 wk of feeding: regular diet (RG), 10% flaxseed-supplemented diet (FX), 0.5% cholesterol-supplemented diet (CH), and 0.5% cholesterol- and 10% flaxseed-supplemented diet (CF). Cholesterol feeding resulted in elevated plasma cholesterol levels and the development of atherosclerosis. The CF group had significantly less atherosclerotic lesions in the aorta and carotid arteries after 6 and 8 wk than the CH animals. However, the anti-atherogenic effect of flaxseed supplementation was completely attenuated by 16 wk. Maximal tension induced in aortic rings either by KCl or norepinephrine was not impaired by dietary cholesterol until 16 wk. This functional impairment was not prevented by including flaxseed in the high-cholesterol diet. Aortic rings from the cholesterol-fed rabbits exhibited an impaired relaxation response to acetylcholine at all time points examined. Including flaxseed in the high-cholesterol diet completely normalized the relaxation response at 6 and 8 wk and partially restored it at 16 wk. No significant changes in the relaxation response induced by sodium nitroprusside were observed in any of the groups. In summary, dietary flaxseed is a valuable strategy to limit cholesterol-induced atherogenesis as well as abnormalities in endothelial-dependent vasorelaxation. However, these beneficial effects were attenuated during prolonged hypercholesterolemic conditions.     

Contribution of EDRF and EDHF to restoration of endothelial function following dietary restrictions in hypercholesterolemic rats

The mechanisms underlying the impairment of endothelium-mediated vasorelaxation induced by dietary hypercholesterolemia and the mechanisms of restoration of endothelial function following reintroduction of low cholesterol diet were evaluated. Feeding rats with high cholesterol diet induced hypercholesterolemia and high blood pressure. This was associated with reduced vasorelaxation in response to acetylcholine, isoproterenol, and adenosine. At the same time, exaggerated contractile responses to serotonin and phenylephrine were observed. Reintroduction of a normal diet to cholesterol fed rats resulted in significant normalization of blood pressure, serum lipid profile, relaxation and contractile responses. The contributions of endothelial derived relaxing factors (EDRF), endothelial derived contractile factors (EDCFs)/prostanoids, and endothelial derived hyperpoalrising factor (EDHF) to the vasorelaxation in each group of animals were assessed. EDCFs constricting activity was increased in both cholesterol fed groups as compared to the control group. EDRF and EDHF were found to be the primary factors involved in the regulation of endothelium-mediated responsiveness. In control animals, EDRF was responsible for 70-90% of relaxation, depending on the agonist used. In cholesterol fed animals, EDRF was significantly reduced while EDHF was maintained or enhanced showing that EDHF had a significant role in maintaining the endothelial responses. Importantly, the restoration of vasorelaxation following reintroduction of normal diet was mediated not only by improvement of EDRF-dependent relaxation, but also to a significant extent by a further increase in EDHF-mediated relaxation. Taken together, the data showed that EDRF was attenuated during hypercholesterolemia and dietary interventions with low fat content restored these responses. However, EDHF-mediated responses were not reduced by hypercholesterolemia and subsequently improved their function after application of low cholesterol diet. The results implicate EDHF-mediated relaxation is also an important mechanism for restoration of endothelial function upon application of dietary restrictions for reduction of serum cholesterol level.     

Influence of oxygen tension on myocardial performance. Evaluation by tissue Doppler imaging

Background

Endothelial function in hypercholesterolemic rabbits is usually evaluated ex vivo on isolated aortic rings. In vivo evaluation requires invasive imaging procedures that cannot be repeated serially.

Aim

We evaluated a non-invasive ultrasound technique to assess early endothelial function in rabbits and compare data with ex vivo measurements.

Methods

Twenty-four rabbits (fed with a cholesterol diet (0.5%) for 2 to 8 weeks) were given progressive infusions of acetylcholine (0.05–0.5 μg/kg/min) and their endothelial function was assessed in vivo by transcutaneous vascular ultrasound of the abdominal aorta. Ex vivo endothelial function was evaluated on isolated aortic rings and compared to in vivo data.

Results

Significant endothelial dysfunction was demonstrated in hypercholesterolemic animals as early as 2 weeks after beginning the cholesterol diet (aortic cross-sectional area variation: -2.9% vs. +4% for controls, p < 0.05). Unexpectedly, response to acetylcholine at 8 weeks was more variable. Endothelial function improved in 5 rabbits while 2 rabbits regained a normal endothelial function. These data corroborated well with ex vivo results.

Conclusion

Endothelial function can be evaluated non-invasively in vivo by transcutaneous vascular ultrasound of the abdominal aorta in the rabbit and results correlate well with ex vivo data.     

Zinc supplementation inhibits lipid peroxidation and the development of atherosclerosis in rabbits fed a high cholesterol diet

Developing atherosclerotic lesions in hypercholesterolemic rabbits are depleted in zinc, while iron accumulates. This study examined the influence of zinc supplementation on the development of atherosclerosis and used isotope dilution gas chromatography-mass spectrometry techniques to measure biomarkers of oxidative lipid damage in atherosclerotic rabbit aorta. Our previous method for F(2)-isoprostane measurement was adapted to include the quantitation of cholesterol oxidation products in the same sample. Two groups of New Zealand white rabbits were fed a high cholesterol (1% w/w) diet and one group was also supplemented with zinc (1 g/kg) for 8 weeks. Controls were fed a normal diet. Zinc supplementation did not significantly alter the increase in total plasma cholesterol levels observed in animals fed high cholesterol. However, in cholesterol-fed animals zinc supplementation significantly reduced the accumulation of total cholesterol levels in aorta which was accompanied by a significant reduction in average aortic lesion cross-sectional areas of the animals. Elevated levels of cholesterol oxidation products (5,6-alpha and beta cholesterol epoxides, 7beta-hydroxycholesterol, 7-ketocholesterol) in aorta and total F(2)-isoprostanes in plasma and aorta of rabbits fed a cholesterol diet were significantly decreased by zinc supplementation. Our data indicate that zinc has an antiatherogenic effect, possibly due to a reduction in iron-catalyzed free radical reactions.     

Endothelium-dependent relaxation and experimental atherosclerosis in the rabbit aorta

This study was undertaken to determine whether the production or release of the endothelium-dependent relaxatory factor is impaired in atherosclerotic New Zealand White rabbits. Atherosclerosis was induced by feeding a diet containing 2% cholesterol for 6 weeks. The production or release of endothelium-dependent relaxatory factor was assayed as follows. A 5-cm length of aorta donor was perfused with Krebs-bicarbonate buffer and the perfusate drained over a deendothelialized ring of recipient aorta set up for recording isometric tension. The recipient was precontracted with norepinephrine (0.2 mumol/L) in the perfusate. When acetylcholine was added to the perfusate, the recipient relaxed in a dose-dependent manner. This assay was used to compare the relaxatory responses produced in recipient rings by adding acetylcholine to donors from atherosclerotic and control rabbits. The relaxation produced by atherosclerotic donors were smaller than those generated by control donors (16.5 +/- 4.9 vs. 32.7 +/- 5.3%; n = 10, p less than 0.05). It is suggested that in atherosclerotic rabbits the ability of aortic endothelium to produce or release endothelium-dependent relaxatory factor is impaired.     

Hazelnut oil administration reduces aortic cholesterol accumulation and lipid peroxides in the plasma, liver, and aorta of rabbits fed a high-cholesterol diet

Hazelnut oil (HO) is rich in monounsaturated fatty acids and antioxidants. We wanted to investigate the effect of HO on lipid levels and prooxidant-antioxidant status in rabbits fed a high-cholesterol (HC) diet. An HC diet caused significant increases in lipids and lipid peroxide levels in the plasma, liver, and aorta together with histopathological atherosclerotic changes in the aorta. Glutathione levels, glutathione peroxidase, and glutathione transferase activities decreased significantly, but superoxide dismutase activity and vitamin E and C levels remained unchanged in the livers of rabbits following HC diet. HO supplementation reduced plasma, liver, and aorta lipid peroxide levels and aorta cholesterol levels together with amelioration in atherosclerotic lesions in the aortas of rabbits fed an HC diet, without any decreasing effect on cholesterol levels in the plasma or liver. HO did not alter the antioxidant system in the liver in the HC group. Our findings indicate that HO reduced oxidative stress and cholesterol accumulation in the aortas of rabbits fed an HC diet.     

Effects of cholesterol diets on vascular function and atherogenesis in rabbits

Vascular endothelial dysfunction is an important early event in atherogenesis. To evaluate the effects of different levels of cholesterol-containing diets on vascular function and atherogenesis, 17 New Zealand White male rabbits were randomized into four groups: Control with noncholesterol, 10-week 0.5% (0.5C-10) or 1% cholesterol (1C-10), and 14-week 0.5% cholesterol (0.5C-14) feedings. After 10 or 14 weeks, the aortas were harvested for studies of vascular endothelial function and percentage surface lipid lesions. The 0.5% and 1% cholesterol feedings resulted in the same degree of hypercholesterolemia independent of the level and period of cholesterol feeding. There was a decreased trend in vascular endothelial-dependent relaxation to acetylcholine in cholesterol-fed rabbits. Fourteen-week cholesterol feeding induced the least vascular dilation at a concentration of 10-7 M acetylcholine (-38 +/- 3%, -23 +/- 4%, -23 +/- 2%, and -15 +/- 5% in control, 0.5C-10, 1C-10, and 0.5C-14 groups, respectively, P = 0.003). More cumulative exposure of arterial walls to cholesterol induced more surface lipid lesions in the aorta (r = 0.877, P < 0.001). There was a negative relationship between aortic lesions and vasodilation (r = -0.557, P = 0.020 for calcium ionophore; r = -0.463, P = 0.062 for acetylcholine). We conclude that the 0.5% and 1% cholesterol feedings induce similar degrees of hypercholesterolemia. However, aortic lipid lesions and vascular reactivity are dependent on cumulative exposure to cholesterol rather than serum cholesterol level only. Furthermore, decreased vascular endothelial relaxation in cholesterol-fed rabbits was related to lipid plaques in the aorta.     

17β-雌二醇对去卵巢胰岛素抵抗大鼠主动脉舒缩功能损伤的保护作用

为观察17β-雌二醇（17beta-estradiol,17β-E2）对去卵巢胰岛素抵抗（insulin resistance,IR）大鼠主动脉结构和舒缩功能的影响及其可能机制,成年雌性Sprague-Dawley大鼠卵巢切除后,高果糖喂养8周诱导IR,同时给予生理剂量的17β-E2（30μg／kg）,每天皮下注射一次,并检测IR相关指标。大鼠胸主动脉石蜡切片,HE染色,图像分析系统测定其结构。采用血管环灌流法,观察各组大鼠胸主动脉环对新福林（L-phenylephrine,PE）的收缩反应和对ACh、硝普钠（sodium nitroprusside,SNP）的舒张反应以及一氧化氮合酶（nitric oxide synthase,NOS）抑制剂N-硝基-L-精氨酸甲脂（N-nitrl-L-arginine methylester,L-NAME）对卵巢切除＋果糖喂养＋17β-E2组大鼠胸主动脉ACh的舒张反应的影响;检测各组大鼠一氧化氮（nitric oxide,NO）含量。结果显示：（1）17β-E2能防止高果糖诱导的去卵巢IR人鼠收缩压升高、高胰岛素血症和胰岛素敏感性下降;（2）各组火鼠胸主动脉的结构无显著性差异;（3）卵巢切除＋果糖喂养组大鼠与卵巢切除组或果糖喂养组相比,血清NO显著降低,胸主动脉对PE的收缩反应显著增强,对ACh的舒张反应显著降低,17β-E2能逆转上述改变,L-NAME可部分阻断17β-E2的这种作用;（4）各组大鼠胸主动脉对SNP的舒张反应和去内皮后对PE的收缩反应均无显著差异。以上结果表明,17β-E2能抑制高果糖诱导的去卵巢IR大鼠血管舒缩功能的紊乱,其机制一方面可能是部分通过血管内皮细胞NOS途径促进NO的释放,保护内皮细胞;另一方面可能是通过降低血压,血清胰岛素水平,改善IR所致。     

Comparison of endothelial function in the carotid artery between normal and short-term hypercholesterolemic rabbits

The present study was undertaken to investigate and compare the vascular function in carotid arteries isolated from normal short-term hypercholesterolemic rabbits. Rabbits were fed normal or 0.5% cholesterol chow for 5 weeks. The tension of isolated carotid artery rings was measured isometrically. Serum lipid levels were measured and morphometric analysis was performed. And content of nitrate/nitrite in the carotid artery was also determined. In the carotid artery precontracted by phenylephrine, the cholesterol chow diet administered for 5 weeks decreased acetylcholine-induced relaxation at only middle concentrations, though it significantly increased the content of nitrate/nitrite, the sum of stable nitric oxide metabolites, in the carotid artery. Cholesterol chow for 5 weeks had no influence on sodium nitroprusside-induced relaxation in the carotid artery. The N(G)-nitro-L-arginine- and indomethacin-resistant endothelium-dependent relaxation induced by acetylcholine was significantly decreased in rabbits receiving the cholesterol chow as compared to rabbits receiving the control diet. The resistant part of acetylcholine-induced relaxation was significantly inhibited when the carotid artery was treated with glibenclamide, a selective inhibitor of ATP-sensitive K(+) channels, 4-aminopyridine, an inhibitor of voltage-dependent K(+) channels, or charybdotoxin, an inhibitor of large and intermediate conductance Ca(2+)-activated K(+) channels, and it was significantly inhibited by tetraethylammonium, a non-selective inhibitor of Ca(2+)-activated K(+) channels and N,N-di-ethylaminoethyl-2,2-diphenylvalerate hydrochloride (SKF 525a), a nonselective cytochrome P-450 monooxygenase (CYP) inhibitor, or ketoconazole, a selective CYP3A inhibitor in only normal rabbits. These results suggest that short-term hypercholesterolemia decreased EDHF-induced relaxation mediated through K(+) channels in rabbit carotid artery and that it may be due partially to the inhibition of CYP3A system in the carotid artery at an early stage of hypercholesterolemia.     

Adipophilin在动脉粥样硬化病变和脂质负荷细胞中的作用研究(英文)

Adipophilin是细胞内脂质聚集和与脂质聚集有关疾病的标志物 ,巨噬细胞源性泡沫细胞的形成是动脉粥样硬化性疾病发生的重要环节 .为了探讨adipophilin在动脉粥样硬化性疾病的作用 ,通过高胆固醇饲料喂养新西兰白兔 12周 ,复制动脉粥样硬化疾病模型 ,同时测定血脂的变化和动脉壁胆固醇 ,使用HE染色、苏丹Ⅳ染色观察动脉粥样硬化病变的形成 ,使用免疫组织化学的方法观察动脉粥样硬化病变处和动物肝脏中adipophilin的表达 .结果发现 ,高胆固醇饲料喂养组血清总胆固醇、低密度脂蛋白胆固醇和动脉壁胆固醇明显增高 ,动脉粥样硬化病变面积增加到 (40 0 6± 7 2 9) % ,动脉粥样硬化病变处adipophilin表达呈阳性 ;而adipophilin在肝脏中的表达无论是高胆固醇饲料喂养组或对照组均为阴性 .使用80mg/L OxLDL与小鼠腹膜巨噬细胞共孵育 ,复制脂质负荷细胞 ,然后把构建的 1mmol/Ladipophilin反义寡核苷酸与该细胞共孵育 .结果发现 ,使用油红O染色观察的细胞内脂滴明显减少 ,生化测定细胞内胆固醇酯显著降低 ,与对照组相比 ,差别有显著性 .说明adipophilin与动脉粥样硬化病变有密切的关系 ,控制adipophilin的表达能够减少巨噬细胞细胞内胆固醇酯的聚集     

Does a HDL injection reduce the development of serum hyperlipidemia and progression of fatty streaks in cholesterol fed rabbits?

The influences of homologous (rabbit) or heterologous (human) high density lipoprotein (HDL) on the development of serum hyperlipidemia and progression of fatty streaks were studied in cholesterol fed rabbits. Three groups of New Zealand rabbits were fed a 0.5% cholesterol rich diet for 8 weeks. Additionally into these animals the following solutions were injected intravenously two times per week: group 1 (control): saline; group 2: human HDL dissolved in saline; group 3: rabbit HDL dissolved in saline. The animals of group 2 had lower serum cholesterol levels during the dietary period than rabbits of group 1 (p < 0.05) but the surface of intima covered with fatty streaks was the same as in group 1. On the other hand, the serum cholesterol level in rabbits of group 3 was the same as in group 1 during the whole experimental period, but the surface of aorta covered with fatty streaks was significantly lower (p < 0.05) in group 3 than in group 1. The results of this study support the hypothesis of an antiatherogenic action of HDL, which seems to be independent of the influence of HDL on the serum lipids but depends on the source of HDL.     

Induction of apolipoprotein E gene expression in human and experimental atherosclerotic lesions

Hypercholesterolemia and atherosclerosis were induced in New Zealand White rabbits by cholesterol feeding. Apolipoprotein E mRNA levels in livers were found to be slightly increased, as determined by Northern blots. Apolipoprotein E gene expression was dramatically induced in rabbit atherosclerotic aortas with respect to healthy aortas. However, apolipoprotein E mRNA levels in atherosclerotic aortas were low as compared with the hepatic mRNA levels of the same animals. Interestingly, we also found a significant increase in apolipoprotein E expression in human atheromata with respect to healthy aorta from the same individual. This is the first report on apo E gene induction in human atherosclerotic lesions.     

Effect of high-salt diet on NO release and superoxide production in rat aorta

Sprague-Dawley rats were fed either a high-salt (HS) diet (4.0% NaCl) or a low-salt (LS) diet (0.4% NaCl) for 3 days. Nitric oxide (NO) and superoxide production were assessed in the thoracic aorta by evaluating the fluorescence signal intensity from 4,5-diaminofluorescein (DAF-2DA) and dihydroethidine, respectively. Methacholine caused increased NO release in the aortas from rats on a LS but not HS diet. The SOD mimetic tempol restored methacholine-induced NO release in aortas from rats on a HS diet. Methacholine also caused superoxide production in the aortas of rats on a HS diet but not in the aortas of rats on a LS diet. Tempol and N(G)-monomethyl-l-arginine eliminated methacholine-induced superoxide production in the aortas of rats on a HS diet. Aortic rings from rats on the HS diet showed impaired methacholine-induced relaxation, which was improved by tempol. Tempol alone caused a NO-dependent relaxation of norepinephrine-precontracted aortas that was significantly greater in the aortas of rats on the HS diet than in vessels from rats on the LS diet. These data suggest that a HS diet impairs endothelium-dependent relaxation via reduced NO levels and increased superoxide production.     

Effects of taurine on the reactivity of aortas from diabetic rats

The effects of the semi-essential amino acid-like nutrient, taurine, on alterations in the reactivities of aortas from male rats with chronic streptozotocin-induced diabetes were examined under in vitro conditions. In the absence of taurine, the contractile responsiveness of endothelium-denuded aortic rings from diabetic rats to norepinephrine, but not KCl, was enhanced compared to controls. This effect of norepinephrine on the diabetic rat aorta appeared to be associated with increased release of intracellular calcium, influx of extracellular calcium and protein kinase C-mediated responses. Incubation of endothelium-denuded aortic rings with 10 mM, but not 5 mM, taurine for 2 h reduced the augmented contractile responses of the tissues from diabetic rats to norepinephrine close to control levels, and this was associated with inhibition of responses linked to the release and influx of calcium, and protein kinase C activation. Endothelium-dependent relaxation of aortas from diabetic rats to acetylcholine was depressed relative to controls. This effect of diabetes was ameliorated close to control levels by incubating the tissues with 10 mM, but not 5 mM, taurine for 2 h. Incubation of nondiabetic rat aortic rings with 45 mM glucose for 3 h caused enhancement of contraction of the vascular smooth muscle to phenylephrine and impairment of endothelium-mediated vasorelaxation to acetylcholine, as compared to control responses. Co-incubation of the tissues with 5-10 mM taurine concentration-dependently reduced the alterations in both contractile and relaxant responses caused by high glucose. Overall, the data suggest that taurine ameliorates or prevents vascular reactivity alterations in diabetes. Such an observation provides preliminary evidence for taurine's potential as a therapeutic agent for the prevention or amelioration of vascular disorders in diabetes.     

Effect of dietary cholesterol and alloxan-diabetes on tissue cholesterol and apolipoprotein E mRNA levels in the rabbit

Alloxan-diabetic rabbits develop hypercholesterolemia and hypertriglyceridemia in response to cholesterol feeding. To determine whether alterations in apolipoprotein composition of plasma lipoproteins were due to changes in apolipoprotein gene expression, we measured the steady state apoE mRNA levels in several tissues from both control and diabetic rabbits. Control rabbits were fed either chow or chow plus 1.5% cholesterol (chow-fed or cholesterol-fed groups) and diabetic rabbits were fed either chow or chow plus 0.5% cholesterol for dietary periods of 5, 21, and 42 days. The tissues examined were liver, small intestine, brain, adrenals, and aorta. ApoE mRNA levels were measured by Northern and dot blot analysis with a human apoE cDNA probe. In control rabbits fed either chow or cholesterol diets for up to 42 days, the steady state apoE mRNA levels remained relatively constant in all of the tissues examined. In contrast, in alloxan-diabetic rabbits fed a 0.5% cholesterol diet, apoE mRNA was reduced in liver, brain, and adrenals (46 +/- 19%, 56 +/- 5%, and 39 +/- 18% of chow-fed control, respectively), but showed little change in the aorta (91 +/- 22% of chow-fed control). Despite a similar increase in plasma cholesterol, the cholesterol content of the liver and adrenals of cholesterol-fed diabetic rabbits were 20% and 50%, respectively, of that of the liver and adrenals in cholesterol-fed control rabbits. The result that apoE mRNA levels and tissue cholesterol content are altered in the diabetic cholesterol-fed rabbit suggests that insulin deficiency in the rabbit may influence apoE gene expression and tissue cholesterol homeostasis.     

Dietary copper deficiency and endothelium-dependent relaxation of rat aorta.

Endothelium-dependent relaxation of aortas was studied in dietary copper (Cu) deficiency. Male, weanling Sprague-Dawley rats were fed diets deficient (CuD, less than 0.5 ppm) or adequate (CuA, 5.0-5.5 ppm) in Cu for 4 weeks. Aortic rings from paired Cu-deficient and Cu-adequate rats were isolated from the descending thoracic aorta, placed in tandem tissue baths, and attached to force transducers. Aortas were contracted with phenylephrine (3 x 10(-7) M) and the degree of force reduction was measured after successively increasing the dose of acetylcholine (10(-8)-10(-5) M), histamine 10(-6)-10(-3) M), or sodium nitroprusside (10(-9)-10(-6) M). Cu deficiency was found to significantly reduce the relaxation responses of each relaxing agent at the highest three of the four doses tested. The ability of Cu-adequate and Cu-deficient aortas to relax was not different, as indicated by their complete relaxation in response to 10(-4) or 10(-5) M papaverine. Because the relaxation responses to both acetylcholine and histamine in rat aorta are dependent on the presence of endothelium, the reduction of these responses suggests that endothelium, or its interaction with smooth muscle, was disrupted in dietary Cu deficiency. The reduction in response to sodium nitroprusside, an endothelium-independent analog of endothelium-derived relaxing factor, indicates that the interaction of endothelium-derived relaxing factor with smooth muscle was disrupted. These findings have implications regarding blood pressure regulation in Cu deficiency.     

Production of platelet thromboxane A2 and arterial prostacyclin I2 from hypercholesterolemic rats.

The plasma cholesterol, plasma malonaldehyde (MDA), platelet thromboxane A2 (TXA2) and vascular prostacyclin (PGI2) were measured in male Sprague-Dawley rats fed diets supplemented with cholesterol (1%) and cholic acid (0.5%). For comparisons, measurements were made in rats fed normal diets. The concentration of cholesterol in the plasma of rats had reached a maximum in 1 week of feeding experimental diets. TXA2 production from collagen and thrombin stimulated platelets was significantly decreased in animals fed experimental diets for 1 week. The production of MDA in the plasma of animals fed experimental diets for 8 weeks was significantly lower compared to the animals fed normal diets. There was a small but significant reduction in the formation of PGI2 in rats fed experimental diets for 8 weeks. These data suggest that feeding cholesterol rich diets to rats alters the platelet membrane properties differently from human and rabbit. Furthermore, cholesterol feeding to rats had some damaging effect on the arterial PGI2 synthesis.     

Association of aorta intima permeability with myosin light chain kinase expression in hypercholesterolemic rabbits

The development of hypercholesterolemia is a multifactorial process in which elevated plasma cholesterol levels play a central role. This study analyzed the variability of the expression and activity of myosin light chain kinase (MLCK) and endothelial permeability in the artery wall of rabbits after feeding the animals with a normal or a high-cholesterol diet. Hypercholesterolemia was induced by a high-cholesterol diet for 4 weeks. Aortas were removed and analyzed for endothelial permeability and MLCK expression. Samples of the arterial media were analyzed for MLCK activity and expression. A selective MLCK inhibitor 1-(5-iodonaphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine hydrochloride (ML7) were used in hypercholesterolemia rabbit (1 mg/kg body weight). The aortas of high-cholesterol diet rabbits showed an increase in MLCK expression and activity (nearly threefold compare with control) as well as endothelial permeability. ML7 inhibit MLC phosphorylation and MLCK activity (nearly twofold compare with control) and endothelial permeability stimulated by cholesterol. These results indicate for the first time that hypercholesterolemia may be associated with MLCK expression and activity through which endothelial permeability is increased.