Antioxidants restore aortic ring relaxation in pancreatectomized rats

Vascular response was assessed in rats made diabetic by subtotal pancreatectomy (PPx). Adult male Wistar rats submitted to PPx eight weeks earlier, and exhibiting altered levels of fasting glucose and an abnormal tolerance glucose test, were used. Sham-operated laparotomized rats were employed as controls. Dose-response curves for acetylcholine-induced, endothelium-related relaxation of aortic rings (after previous exposure to phenylephrine) were conducted in a high glucose solution (44 mmol/L). PPx decreased significantly acetylcholine-induced relaxation only in the presence of a high glucose solution (p<0.00001). Tiron, superoxide dismutase (SOD) or melatonin restored altered aortic relaxation. Melatonin, SOD or Tiron were equally effective in restoring the impaired sodium nitroprusside-induced vasorelaxation in endothelium-denuded aortic rings of PPx rats. The results support the evidence about the ability of antioxidants to restore altered vascular reactivity of aortic rings in PPx rats, probably through the scavenging property of superoxide anion accumulation.     

Comparative effects of melatonin and vitamin E in restoring aortic relaxation in pancreatectomized rats

In a previous study we reported the efficacy of melatonin to restore the decreased relaxation response to acetylcholine (ACh) or to sodium nitroprusside (SNP) in aortic rings of rats turned hyperglycemic by subtotal pancreatectomy. The effect was amplified by pre-incubation in a high (44 mmol/l) glucose solution, a situation that resulted in oxidative stress. We hereby compare the effect of another antioxidant, vitamin E, with that of melatonin on ACh response in intact aortic rings or on SNP response in endothelium-denuded aortic rings obtained from pancreatectomized or sham-operated rats. Dose-response curves to ACh or SNP were performed in the presence or absence of melatonin or vitamin E (10-5 mol/1) in 10 or 44 mmol/1 glucose medium. Melatonin was more effective than vitamin E in restoring ACh- or SNP-induced relaxation of aortic rings in a high glucose medium. The differences between the two antioxidants may rely on the ability of melatonin to diffuse readily into intracellular compartments.     

Garlic extract attenuates time-dependent changes in the reactivity of isolated aorta in streptozotocin-diabetic rats

In the present study, the effect of aqueous garlic extract (Allium sativum; 100 mg/Kg/day; i.p.) on the vascular reactivity of streptozotocin (STZ)-diabetic rats was investigated. Vascular reactivity of isolated aortic rings was assessed by measuring phenylephrine-induced contractile and acetylcholine-induced relaxation responses. The results showed that aortas prepared from 8-week, but not 4-week, STZ-diabetic rats exhibited significantly increased contractile responses, which were partially attenuated by garlic extract treatment. The maximum vasorelaxant response of pre-contracted aortic rings exposed to acetylcholine also significantly decreased in 8-week STZ-diabetic animals which was attenuated to some extent by extract treatment. It is concluded that long-term administration of garlic extract (i.p.) can attenuate various functional alterations induced by STZ-diabetes in the vascular system of an insulin-dependent model of uncontrolled diabetes, and this may suggest a potential approach to future therapeutic strategies.     

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.     

Quercetin, a flavonoid antioxidant, modulates endothelium-derived nitric oxide bioavailability in diabetic rat aortas

The present work examined the effect of chronic oral administration of quercetin, a flavonoid antioxidant, on blood glucose, vascular function and oxidative stress in STZ-induced diabetic rats. Male Wistar-Kyoto (WKY) rats were randomized into euglycemic, untreated diabetic, vehicle (1% w/v methylcellulose)-treated diabetic, which served as control, or quercetin (10mgkg(-1) body weight)-treated diabetic groups and treated orally for 6 weeks. Quercetin treatment reduced blood glucose level in diabetic rats. Impaired relaxations to endothelium-dependent vasodilator acetylcholine (ACh) and enhanced vasoconstriction responses to alpha(1)-adrenoceptor agonist phenylephrine (PE) in diabetic rat aortic rings were restored to euglycemic levels by quercetin treatment. Pretreatment with N(omega)-nitro-l-arginine methyl ester (l-NAME, 10microM) or methylene blue (10microM) completely blocked but indomethacin (10microM) did not affect relaxations to ACh in aortic rings from vehicle- or quercetin-treated diabetic rats. PE-induced vasoconstriction with an essentially similar magnitude in vehicle- or quercetin-treated diabetic rat aortic rings pretreated with l-NAME (10microM) plus indomethacin (10microM). Quercetin treatment reduced plasma malonaldehyde (MDA) plus 4-hydroxyalkenals (4-HNE) content as well as increased superoxide dismutase activity and total antioxidant capacity in diabetic rats. From the present study, it can be concluded that quercetin administration to diabetic rats restores vascular function, probably through enhancement in the bioavailability of endothelium-derived nitric oxide coupled to reduced blood glucose level and oxidative stress.     

Desensitization of alpha-1 adrenergic receptor mediated smooth muscle contraction in aorta from endotoxic rats

Desensitization of vascular smooth muscles in endotoxemia was studied using the aorta from intraperitoneally endotoxin-injected rats. The KCl- and phenylephrine-induced contractions were significantly decreased in the endotoxic aorta compared to the control. In the endotoxic aorta the phenylephrine-induced contracture showed a gradual tension decrease after reaching a plateau and was attenuated by prior exposure to high concentration of phenylephrine, while KCl produced a sustained contraction and it was not affected by prior exposure to phenylephrine. The phenylephrine- and KCl-induced contractures of the control aorta showed stable plateaus and were not affected by prior exposure to phenylephrine. Neither diminished contractile force nor in vitro desensitization of phenylephrine contracture of isolated aorta was prevented by pretreatment of endotoxic rats with an alpha-adrenergic antagonist, phentolamine. These findings suggest that the contractile response to phenylephrine is easily desensitized in the endotoxic aorta compared to the control and neither this in vitro desensitization nor the diminution of contractile force is caused by in vivo exposure of aorta to a high concentration of catecholamines during endotoxemia.     

Low mercury concentrations cause oxidative stress and endothelial dysfunction in conductance and resistance arteries

Increased cardiovascular risk after mercury exposure has been described, but the underlying mechanisms are not well explored. We analyzed the effects of chronic exposure to low mercury concentrations on endothelium-dependent responses in aorta and mesenteric resistance arteries (MRA). Wistar rats were treated with mercury chloride (1st dose 4.6 microg/kg, subsequent dose 0.07 microg.kg(-1).day(-1) im, 30 days) or vehicle. Blood levels at the end of treatment were 7.97 +/- 0.59 ng/ml. Mercury treatment: 1) did not affect systolic blood pressure; 2) increased phenylephrine-induced vasoconstriction; 3) reduced acetylcholine-induced vasodilatation; and 4) reduced in aorta and abolished in MRA the increased phenylephrine responses induced by either endothelium removal or the nitric oxide synthase (NOS) inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME, 100 microM). Superoxide dismutase (SOD, 150 U/ml) and the NADPH oxidase inhibitor apocynin (0.3 mM) decreased the phenylephrine-induced contraction in aorta more in mercury-treated rats than controls. In MRA, SOD did not affect phenylephrine responses; however, when coincubated with l-NAME, the l-NAME effect on phenylephrine response was restored in mercury-treated rats. Both apocynin and SOD restored the impaired acetylcholine-induced vasodilatation in vessels from treated rats. Endothelial NOS expression did not change in aorta but was increased in MRA from mercury-treated rats. Vascular O2(-) production, plasmatic malondialdehyde levels, and total antioxidant status increased with the mercury treatment. In conclusion, chronic exposure to low concentrations of mercury promotes endothelial dysfunction as a result of the decreased NO bioavailability induced by increases in oxidative stress. These findings offer further evidence that mercury, even at low concentrations, is an environmental risk factor for cardiovascular disease.     

Interaction between endothelial heme oxygenase-2 and endothelin-1 in altered aortic reactivity after hypoxia in rats

The aim of this study was to determine whether increased expression of heme oxygenase (HO) contributes to impairment of aortic contractile responses after hypoxia through effects on reactivity to endothelin-1 (ET-1). Thoracic aortas from normoxic rats and rats exposed to hypoxia (10% O2) for 16 or 48 h were mounted in organ bath myographs for contractile studies, fixed in paraformaldehyde, or frozen in liquid nitrogen for protein extraction. In rings from normoxic rats, the HO inhibitor tin protoporphyrin IX (SnPP IX, 10 microM) did not alter the response to phenylephrine or ET-1. In rings from rats exposed to 16-h hypoxia, maximum tension generated in response to these agonists was higher in endothelium-intact but not -denuded rings in the presence of SnPP IX. In rings from rats exposed to 48-h hypoxia SnPP IX increased contraction in endothelium-intact but not -denuded rings. In endothelium-intact aortic rings from rats exposed to 16-h hypoxia incubated with endothelin A receptor-specific antagonist BQ-123 (10(-7) M), SnPP IX did not alter phenylephrine-induced contraction. Aortic ET-1 protein levels, measured by radioimmunoassay, were increased in rats exposed to hypoxia for 16 and 48 h. Western blotting showed that HO-1 and HO-2 protein were increased after 16 h of hypoxia and returned to near-control levels after 48 h. Increase in HO-1 protein was detected in endothelium-intact and -denuded rings. Removal of endothelium abolished the increase in HO-2 immunoreactivity. Immunohistochemistry localized expression of HO-1 protein to vascular smooth muscle, whereas HO-2 was only detected in endothelium. HO-2 is expressed by aortic endothelial cells early during hypoxic exposure and impairs ET-1-mediated potentiation of contraction to alpha-adrenoceptor stimulation.     

Chronic Lead Exposure Decreases the Vascular Reactivity of Rat Aortas: The Role of Hydrogen Peroxide

We investigated whether exposure to small concentrations of lead alters blood pressure and vascular reactivity. Male Wistar rats were sorted randomly into the following two groups: control (Ct) and treatment with 100 ppm of lead (Pb), which was added to drinking water, for 30 days. Systolic blood pressure (BP) was measured weekly. Following treatment, aortic ring vascular reactivity was assessed. Tissue samples were properly stored for further biochemical investigation. The lead concentration in the blood reached approximately 8 μg/dL. Treatment increased blood pressure and decreased the contractile responses of the aortic rings to phenylephrine (1 nM–100 mM). Following N-nitro-L arginine methyl ester (L-NAME) administration, contractile responses increased in both groups but did not differ significantly between them. Lead effects on R_max were decreased compared to control subjects following superoxide dismutase (SOD) administration. Catalase, diethyldithiocarbamic acid (DETCA), and apocynin increased the vasoconstrictor response induced by phenylephrine in the aortas of lead-treated rats but did not increase the vasoconstrictor response in the aortas of untreated rats. Tetraethylammonium (TEA) potentiated the vasoconstrictor response induced by phenylephrine in aortic segments in both groups, but these effects were greater in lead-treated rats. The co-incubation of TEA and catalase abolished the vasodilatory effect noted in the lead group. The present study is the first to demonstrate that blood lead concentrations well below the values established by international legislation increased blood pressure and decreased phenylephrine-induced vascular reactivity. The latter effect was associated with oxidative stress, specifically oxidative stress induced via increases in hydrogen peroxide levels and the subsequent effects of hydrogen peroxide on potassium channels.     

铁对血管收缩活动的影响及其机制

动脉粥样硬化的发生和铁引起的氧化应激密切相关。铁对血管的直接效应及其对血管收缩功能的影响尚不明确。本文采用血管环灌流装置 ,观察铁对离体SD大鼠去内皮胸主动脉环的直接效应 ,及对去内皮主动脉环KCl和苯肾上腺素 (PE)引发的收缩效应的影响。结果显示 :( 1) 10 0 μmol/L枸橼酸铁 (FAC)引起大鼠血管环发生相位性收缩 ,最大收缩幅度可达KCl诱发的最大收缩的 2 4 0 2± 2 3 7%。当 [Ca2 +]o 增加 1倍时 ,铁所致的血管环收缩幅度明显增加 (P <0 0 1)。阻断L 型钙通道后 ,铁所致的血管环收缩幅度明显降低 (P <0 0 1)。在无钙液中 ,用佛波酯收缩血管环 ,待收缩稳定后给予FAC ,此时收缩幅度增加 49 18± 3 75 %。 ( 2 )铁孵育 3 0min后 ,KCl引起血管环收缩的幅度显著降低 (P <0 0 1)。铁孵育可使PE引起的收缩量 -效曲线右移 (P <0 0 5 )。 ( 3 )二甲基亚砜、过氧化氢酶和谷胱甘肽可明显降低铁对PE血管收缩反应的抑制作用 (P <0 0 5 )。从这些结果可得到以下结论 :铁可引起胸主动脉发生相位性收缩 ,其机制可能与L 型钙通道短暂开放导致钙离子内流 ,及平滑肌对钙的敏感性增加有关 ;较长时间与铁孵育后 ,可对血管收缩功能产生损伤 ,氧自由基的生成增加和细胞内GSH的水平降低可能参与铁对收缩功能的     

The role of extracellular calcium in pregnancy-induced attenuation of phenylephrine contraction in rat aorta with functional endothelium

The effect of pregnancy on the supply of calcium ions for the contractile responses of rat aortic rings to phenylephrine was investigated. The contractility of intact aortic rings from pregnant rats, compared with that of similar rings from non-pregnant rats, to phenylephrine and potassium chloride was significantly decreased. Contractions of rings from non-pregnant rats, pretreated with phenylephrine or potassium chloride, in response to calcium chloride were greater than those of similarly treated rings from pregnant rats. When the concentration of calcium chloride in the medium bathing the rings was reduced to 0.8 mmol·l^-1, the contractile response to phenylephrine was significantly (P<0.005) inhibited in rings from both pregnant and non-pregnant rats but to a greater extent in rings from non-pregnant rats. Contractions of aortic rings from pregnant rats in response to phenylephrine in calcium-free medium were similar to those of rings from non-pregnant rats, suggesting equal dependence on calcium from intracellular stores. The results suggest that pregnancy decreased the response to calcium influx into the aortic smooth muscle cells through both receptor-and voltage-operated calcium entry pathways. Since de-endothelialisation reversed the pregnancy-induced diminished contraction to phenylephrine, it is likely that pregnancy interferred with contractions induced by activation of receptors with phenylephrine through enhanced production of endothelium-derived relaxing factor(s).Abbreviations EC₅₀ concentration of drug producing 50% contraction - EDCF endothelium-derived contraction factor - EGTA ethyleneglycol-bis (-aminoethyl ether)-NN tetraacetic acid - PSS physiological salt solution - VSM vascular smooth muscle     

Reactivity of mesenteric and aortic rings from trained rats fed with high caloric diet

A strong association between the benefits of physical exercise on the cardiovascular disease with an improvement of the endothelium-derived relaxing factor production has been consistently shown. The purpose of this study was to evaluate the effect of exercise training associated with high caloric diet in the reactivity of rat mesenteric and aortic rings. Experimental protocol consisted of 4 weeks of high caloric diet consumption previous to 4 weeks of run training (1.2 km/h, 0% grade, in sessions of 60 min, 5 days/week). Concentrations of triglycerides, glucose, insulin and nitrite/nitrate levels were measured and atherogenic index was calculated. Concentration-response curves to acetylcholine (10 nM-100 microM), sodium nitroprusside (100 pM-100 nM) and phenylephrine (1 nM-3 microM) were obtained. Exercise training reduced body mass (6%) and triglyceride levels (about 54%), without changes in glucose and insulin concentrations. An improvement of endothelium-dependent relaxation responses to acetylcholine in mesenteric and aortic rings was observed in trained group. No changes were seen for sodium nitroprusside and phenylephrine. In conclusion, our study is the first to show clearly that run training promotes an improvement of the endothelium-dependent relaxing response in aorta and mesenteric rings from rats fed with high caloric diet and that is associated with increase of NO production.     

The effect of systemic leptin administration on aorta smooth muscle responses in diabetic rats

Leptin produces effects in central nervous system and peripheral tissues via its specific receptors. Leptin also stimulates nitric oxide release in a concentration-dependent manner. In this study, our aim was to test the hypothesis that whether leptin has a modulatory role on endothelium or smooth muscle function in streptozotocin (STZ)-induced diabetic rats. Wistar-Albino rats were divided into four groups: 1 – Control, 2 – Diabetic, 3 – Control + leptin and 4 – Diabetic + leptin. Experimental diabetes was produced by intraperitoneal injection of a single dose of STZ (55 mg/kg). Diabetes was determined by increased fasting blood glucose level on the 7th day of the experiment. Leptin (0.1 mg/kg/day) was administered intraperitoneally for 5 days. At the end of the 5th day, thoracic aortas were isolated and phenylephrine (Phe)-induced contractions and acetylcholine (ACh)-induced relaxations of each group were estimated. In diabetic rats, Phe-induced contractility was increased (p < 0.05). Leptin pre-treatment increased the Phe-induced contractility significantly in aortic rings obtained from diabetic rats (p < 0.05). In normal rats, leptin administration produced only a slight and non-significant increase in Phe-induced contractions. Although the relaxant responses were decreased in diabetic rats, leptin administration enhanced the ACh-induced relaxation in both normal and diabetic animals significantly. As a conclusion; chronic leptin pre-treatment caused a significant increase both in Phe-induced contractions and ACh-induced Endothelial-Derived Relaxing Factor (EDRF)/Nitric oxide-mediated relaxations in the aortic rings isolated from streptozotocin-induced diabetic rats. This peptide hormone caused a significant increase in the relaxations obtained by ACh while not inducing a significant alteration in the contractile effect of Phe in control rats.     

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.     

Acetylcholine but not adenosine triggers preconditioning through PI3-kinase and a tyrosine kinase

Acrolein is a highly reactive aldehyde pollutant and an endogenous product of lipid peroxidation. Increased generation of, or exposures to, acrolein incites pulmonary and vascular injury. The effects of acrolein on the vasomotor responses of rat aortic rings were studied to understand its mechanism of action. Incubation with acrolein (10-100 microM) alone did not affect the resting tone of aortic vessels; however, a dose-dependent relaxation of phenylephrine-precontracted aortic rings was observed. Acrolein-induced relaxation was slow and time dependent and the extent of relaxation after 100 min of application was 44.7 +/- 4.1% (10 microM), 56.0 +/- 5.6% (20 microM), 61.0 +/- 7.9% (40 microM), and 96.1 +/- 2.1 (80 microM), respectively, versus 14.2 +/- 3.3% relaxation in the absence of acrolein. Acrolein-induced vasorelaxation was prevented by endothelial denudation and was abolished on pretreatment with the nitric oxide synthase inhibitor Nomega-nitro-L-arginine methyl ester, the guanylyl cyclase inhibitor 1H-[1,2,4]oxidazolo[4,3-a]quinoxaline-1-one, or the cyclooxygenase inhibitor indomethacin. Inhibition of K+ channels (by tetrabutylammonium) or Na+-K+-ATPase (by ouabain) did not significantly prevent acrolein-mediated vasorelaxation. Exposure to acrolein in the presence or absence of other compounds elicited slow wave vasomotor effect in 77% of aortic vessels versus 1.4% in control. Vasomotor responses were also studied on aortic rings prepared from rats fed 2 mg. kg-1. day-1 acrolein for 3 alternate days by oral gavage. These vessels developed a significantly lower contractile response to phenylephrine compared with controls. Together, these results indicate that acute acrolein exposure evokes delayed vasorelaxation due to a nitric oxide- and prostacyclin-dependent mechanism, whereas in vivo acrolein exposure compromises vessel contractility.     

Effects of 17ß-estradiol on endothelium-dependent relaxation induced by acetylcholine in female rat aorta

Estrogens have been postulated to play an important role in modulation of vascular responses to endogenous reactive substances. The effects of chronic in vivo treatment with 17ß-estradiol on relaxant responses to acetylcholine were investigated in the rat aorta isolated from prepubertal female rats. The selectivity of effects of 17ß-estradiol on acetylcholine-induced relaxation was evaluated using histamine, another endothelium-dependent relaxant in the rat aorta. 17ß-Estradiol significantly enhanced endothelium-dependent relaxation induced by acetylcholine, but did not alter the vascular responses to acetylcholine in endothelium-denuded aortic rings isolated from prepubertal female rats. In contrast, 17ß-estradiol did not change endothelium-dependent relaxation induced by histamine in endothelium-intact aortic rings. The results of the present study demostrate that 17ß-estradiol selectively enhanced acetylcholine-induced endothelium-dependent relaxation in the rat aorta.     

四氧嘧啶糖尿病大鼠主动脉零应力状态的变化

目的和方法：将沿径向切开的糖尿病大鼠及对照大鼠主动脉坏分别转正圩Ｋｒｅｂｓ液中,向其中分别加入缩血管物质及舒血管物质达各种浓度;观察其角度变化。用Ｓ－Ｐ法对大鼠主动脉壁肌动蛋白进行染色。结果：四氧嘧啶糖尿病大鼠病程４周时主动脉环展开角显著大于对照（Ｐ〈０．００１）。使用药物后大鼠主动脉坏展开角与使用前相比无明显差异（Ｐ〉０．０５）。糖尿病大鼠主动脉壁肌动蛋白色较对照组明显加深、染色的光密度显著大于     

Binding of urokinase to low density lipoprotein-related receptor (LRP) regulates vascular smooth muscle cell contraction

Urokinase plasminogen activator (uPA) is a multifunctional protein that has been implicated in several physiological and pathological processes involving cell adhesion and migration in addition to fibrinolysis. In a previous study we found that two-chain urokinase plasminogen activator (tcuPA) stimulates phenylephrine-induced vasoconstriction of isolated rat aortic rings. In the present paper we report that uPA(-/-) mice have a significantly lower mean arterial blood pressure than do wild type mice and that aortic rings from uPA(-/-) mice show an attenuated contractile response to phenylephrine. In contrast, the blood pressure of urokinase receptor knockout (uPAR(-/-)) mice and the response of their isolated aortic rings to phenylephrine were normal, indicating that the effect of uPA on vascular contraction is independent of uPAR. Addition of mouse and human uPA almost completely reversed both the impaired vascular contractility and the lower arterial blood pressure in vivo. The in vitro and in vivo effects of infused uPA on aortic contractility and the restoration of normal blood pressure in uPA(-/-) mice were prevented by antibody to low-density lipoprotein receptor-related protein/alpha(2)-macroglobulin receptor (LRP). A modified form of uPA that lacks the kringle failed to restore the blood pressure in uPA(-/-) mice, notwithstanding having a longer half-life in the circulation. Ligands that regulate the interaction of uPA with LRP, such as PAI-1 or the PAI-1-derived peptide (EEIIMD), abolished the vasoactivity of tcuPA in vitro and in vivo. These studies identify a novel signal transducing cellular receptor pathway involved in the regulation of vascular contractility.     

Diabetes abolishes the vascular protective effects of estrogen in female rats

Estrogen is known to exert a protective effect against cardiovascular disease. However, women with diabetes have three times the risk as compared with age-matched non-diabetic women. Our previous study on aortic rings of ovariectomized (OVX) female rats treated with 17-beta-estradiol (E2) demonstrated that the beneficial effect of estrogen is related to the basal release of NO from endothelial cells. In the present study, in order to understand why estrogen protection is abolished in diabetes, we tested vascular responses in OVX, streptozotocin-diabetic female rats and their non-diabetic controls receiving or not E2 replacement. Concentration-response curves to norepinephrine (NE) showed attenuation of the contractile response in E2-treated diabetic, with respect to non-diabetic preparations. This response was further impaired in diabetic, E2-deprived rats. The basal release of NO, as evaluated by concentration-related responses to N(G)-methyl-L-arginine acetate in NE-precontracted aortic rings, was found to be impaired in E2-treated diabetic rats, no further effect being induced by E2 deprivation. The endothelium-dependent relaxation produced by carbachol did not change between groups, whereas the relaxation produced by histamine was enhanced by both diabetes and E2 deprivation. However, E2 treatment counteracted the response to histamine only in preparations from non-diabetic animals. Finally, the relaxation induced by sodium nitroprusside, an endothelium-independent relaxant agent, was comparable between groups. These findings suggest that the lack of protective effects of estrogen in diabetes may be mainly ascribed to the failure of estrogen to reverse the impaired basal release of NO and the abnormal relaxation to histamine, which are observed in the aorta of diabetic rats.     

Low-level lead exposure increases systolic arterial pressure and endothelium-derived vasodilator factors in rat aortas

Chronic lead exposure induces hypertension and alters endothelial function. However, treatment with low lead concentrations was not yet explored. We analyzed the effects of 7 day exposure to low lead concentrations on endothelium-dependent responses. Wistar rats were treated with lead (1st dose 4 μg/100 g, subsequent dose 0.05 μg/100 g, i.m. to cover daily loss) or vehicle; blood levels attained at the end of treatment were 9.98 μg/dL. Lead treatment had the following effects: increase in systolic blood pressure (SBP); reduction of contractile response to phenylephrine (1 nM-100 μM) of aortic rings; unaffected relaxation induced by acetylcholine (0.1 nM-300 μM) or sodium nitroprusside (0.01 nM-0.3 μM). Endothelium removal, N(G)-nitro-L-arginine methyl ester (100 μM) and tetraethylammonium (2 mM) increased the response to phenylephrine in treated rats more than in untreated rats. Aminoguanidine (50 μM) increased but losartan (10 μM) and enalapril (10 μM) reduced the response to phenylephrine in treated rats. Lead treatment also increased aortic Na(+)/K(+)-ATPase functional activity, plasma angiotensin-converting enzyme (ACE) activity, protein expression of the Na(+)/K(+)-ATPase alpha-1 subunit, phosphorylated endothelial nitric oxide synthase (p-eNOS), and inducible nitric oxide synthase (iNOS). Our results suggest that on initial stages of lead exposure, increased SBP is caused by the increase in plasma ACE activity. This effect is accompanied by increased p-eNOS, iNOS protein expression and Na(+)/K(+)-ATPase functional activity. These factors might be a compensatory mechanism to the increase in SBP.