Endothelial Dysfunction In Rat Aorta Research Articles

Ginsenoside Rb1 Reduces Hyper-Vasoconstriction Induced by High Glucose and Endothelial Dysfunction in Rat Aorta.

Acute hyperglycemia induces oxidative damage and inflammation, leading to vascular dysfunction. Ginsenoside Rb1 (Rb1) is a major component of red ginseng with anti-diabetic, anti-oxidant and anti-inflammatory properties. Here, we investigated the beneficial effects and the underlying mechanisms of Rb1 on hypercontraction induced by high glucose (HG) and endothelial dysfunction (ED). The isometric tension of aortic rings was measured by myography. The rings were treated with NG-nitro-L-arginine methyl ester (L-NAME) to induce chemical destruction of the endothelium, and Rb1 was added after HG induction. The agonist-induced vasoconstriction was significantly higher in the aortic rings treated with L-NAME + HG50 than in those treated with HG50 or L-NAME (p = 0.011) alone. Rb1 significantly reduced the hypercontraction in the aortic rings treated with L-NAME + HG50 (p = 0.004). The ATP-sensitive K+ channel (KATP) blocker glibenclamide tended to increase the Rb1-associated reduction in the agonist-induced vasoconstriction in the rings treated with L-NAME + HG50. The effect of Rb1 in the aortic rings treated with L-NAME + HG50 resulted from a decrease in extracellular Ca2+ influx through the receptor-operated Ca2+ channel (ROCC, 10-6-10-4 M CaCl2, p < 0.001; 10-3-2.5 × 10-3 M CaCl2, p = 0.001) and the voltage-gated Ca2+ channel (VGCC, 10-6 M CaCl2, p = 0.003; 10-5-10-2 M CaCl2, p < 0.001), whereas Rb1 did not interfere with Ca2+ release from the sarcoplasmic reticulum. In conclusion, we found that Rb1 reduced hyper-vasoconstriction induced by HG and ED by inhibiting the ROCC and the VGCC, and possibly by activating the KATP in rat aorta. This study provides further evidence that Rb1 could be developed as a therapeutic target for ED in diabetes.

A cell permeant phosphopeptide mimetic of Niban restores endothelial function and inhibits p38 MAPK activation after vascular injury

Vascular injury leads to membrane disruption, ATP release, and endothelial dysfunction. Increases in the phosphorylation of p38 MAPK and decreases in the phosphorylation of Niban, a protein implicated in ER stress and apoptosis, are associated with vascular injury. A cell‐permeant phospho‐peptide mimetic of Niban (NiPp) was generated. The effects of NiPp in restoring endothelial function were determined ex vivo using intact rat aortic tissue (RA) after pharmacological activation of p38 MAPK and a clinically relevant stretch injury model. Anisomycin increased p38 MAPK phosphorylation and reduced endothelial‐dependent relaxation in RA. Treatment with NiPp prevented anisomycin‐induced reduction in endothelial function and increase in p38 MAPK phosphorylation (Figure 1). NiPp treatment also restored endothelial function after subfailure overstretch injury (Figure 2). Kinome screening experiments indicated that NiPp inhibits p38 MAPK. These data demonstrate that p38 MAPK and Niban signaling have a role in endothelial function, particularly in response to injury. Niban may represent an endogenous regulator of p38 MAPK activation. NiPp may serve as an experimental tool to further elucidate p38 MAPK regulation and as a potential therapeutic for endothelial dysfunction.Support or Funding InformationThis work was supported by the National Institutes of Health grants R01HL70715‐09 to CB and R01HL105731‐01 to JC.NiPp prevented anisomycin‐induced phosphorylation of p38 MAPK and endothelial dysfunction in rat aorta (RA).RA rings were treated with anisomycin (200μM) in the absence or presence of NiPp (500μM) pretreatment and endothelial function was determined in a muscle bath. A) Representative muscle bath tracings. B) Percent relaxation induced by 0.5μM CCH. C, D) Phosphorylation of p38 MAPK in RA after treatment as determined by Western blot analysis. n=10,*p&lt;.05 in one‐way ANOVA with Tukey post‐test.Figure 1NiPp restored endothelial function and reduced p38MAPK phosphorylation in RA after subfailure stretch injury.RA was subjected to subfailure stretch and incubated in the absence or presence of NiPp (500μM) for 1 h. A) Endothelial‐dependent relaxation was determined in the muscle bath. n=5 rats; #p&lt;.05, two‐way ANOVA. B, C) Phosphorylation of p38 MAPK in RA after stretch injury and NiPp treatment as determined by Western blot analysis n= 10. *p&lt;.05, in one‐way ANOVA with Tukey post‐test.Figure 2

Gender Differences in Sepsis‐Induced Nitric Oxide and EDHF Signaling Pathways in Rat Aorta

Despite recent advances in managing sepsis, it still remains a major health concern in the US. Sepsis is characterized by systemic hypotension, pulmonary hypertension and refractoriness of the vasculature to contractile factors. Nitric Oxide (NO) and Endothelium‐Dependent Hyperpolarizing Factor (EDHF) are crucial in the regulation of vascular tone. The influence of gender on endothelial function in sepsis remains unknown. Therefore, this study was aimed to investigate the influence of gender on sepsis‐induced NO and EDHF signaling pathways in rat aorta. Results indicate that NO and EDHF play a major role in sepsis‐induced endothelial dysfunction in rat aorta in a experimental model of sepsis. Sepsis was induced in rats by cecal ligation and puncture (CLP). 18h after surgery septic rats showed increase in rectal temperature, neutrophilia, pulmonary edema and an increase in plasma nitrate/nitrite levels. However, mean arterial pressure was decreased. Arterial vasoreactivity was measured using an isometric tension protocol. Phenylephrine (PE) was more potent in contracting aortic rings from female than male rats, but the amplitude of contraction was identical in both the sexes. Sepsis significantly decreased the efficacy of PE in aortas from both the sexes. Acetylcholine (ACh) elicited concentration‐dependent relaxation in endothelium intact aortas from male and female rats. Sepsis had no significant effect on the endothelium‐dependent relaxation in the female aorta, but caused significant reduction in the maximal response to ACh in male aortas. There was no evidence of EDHF activity in aortic rings from either sex. Sodium nitroprusside (SNP) was more potent in dilating aortas from male than female rats. Sepsis had no significant effect on the potency or efficacy of SNP‐induced dilation in both genders. Real time PCR was used to measure mRNA expression levels of potassium channels important in the endothelium. In conclusion, the results of present study suggest that sepsis‐induced alteration in the reactivity of aorta to vasoconstrictors or vasodilators is dependent on the gender of the animal.

Endothelial dysfunction in rats with ligature-induced periodontitis: Participation of nitric oxide and cycloxygenase-2-derived products

ObjectivesConsidering the evident relationship between periodontitis and cardiovascular diseases in humans, we aimed to study the in vitro vascular reactivity of aorta rings prepared from rats with ligature-induced periodontitis. MethodsSeven days after the induction of unilateral periodontitis, the animals were euthanised; rings were prepared from the descending abdominal aortas and mounted in tissue baths for the in vitro measurement of the isometric force responses to norepinephrine (NE) and acetylcholine (ACh), as well as in the presence of inhibitors of nitric oxide synthase (NOS) and cycloxygenase (COX) isoenzymes. Aortic COX and NOS gene expressions were analysed by RT-PCR, as well as protein COX-2 expression by Western blot. ResultsPeriodontitis resulted in significant alveolar bone loss and did not affect arterial pressure. However, both NE-induced contraction and ACh-induced relaxation were significantly decreased and related to the presence of endothelium. Diminished eNOS and augmented COX-2 and iNOS expressions were found in the aortas from rats with periodontitis, and the pharmacological inhibition of COX-2 or iNOS improved the observed vasomotor deficiencies. ConclusionsWe can thus conclude that periodontitis induces significant endothelial dysfunction in rat aorta which is characterized by decreased eNOS expression and mediated by upregulated iNOS and COX-2 products.

Induction of Haemeoxygenase-1 Improves FFA-Induced Endothelial Dysfunction in Rat Aorta

Background: The induction of haemeoxygenase-1 (HO-1) exerts beneficial effects in the setting of endothelial dysfunction in obesity. High free fatty acid (FFA) levels are a common feature of obesity and are the primary cause of endothelial dysfunction. The objective of our study was to explore the effects of HO-1 induction on FFA-induced endothelial dysfunction in rats. Methods: Rats received FFA treatment with either cobalt protoporphyrin (CoPP) to induce HO-1 or stannous protoporphyrin (SnPP) to inhibit HO-1. Endothelial function was determined by measuring endothelium-dependent vasodilatation (EDV). Nitric oxide (NO) production, superoxide production and nuclear factor <smlcap>(NF)-</smlcap>κ<smlcap>B </smlcap>expression in the aorta were each determined. The levels of adenosine monophosphate (AMP)-activated kinase (AMPK) and endothelial nitric oxide synthase (eNOS) expression in endothelial cells were determined via Western blotting. Results: Induction of HO-1 by CoPP decreased circulating FFA, high-sensitivity C-reactive protein and malondialdehyde levels and increased serum adiponectin and glutathione levels compared with the FFA group (P<0.05). High FFA levels resulted in EDV impairment, which was improved by HO-1 induction (P<0.05). Induction of HO-1 increased NO levels and reduced aortic superoxide production and <smlcap>NF-</smlcap>κ<smlcap>B </smlcap>expression compared with the FFA group. The FFA group exhibited decreased AMPK expression and eNOS phosphorylation, both of which were enhanced via HO-1 induction (P<0.05). The beneficial effects of CoPP on EDV were partially attenuated in vitro in the presence of inhibitors of AMPK, phosphatidylinositol 3-kinase (PI3K), and eNOS. Conclusions: HO-1 induction with CoPP improves FFA-induced endothelial dysfunction in the rat aorta. The protective mechanism appears to be related to the activation of the AMPK-PI3K-eNOS pathway as a result of increased adiponectin levels as well as decreased inflammation and oxidative stress.

Ganoderma atrum polysaccharide improves aortic relaxation in diabetic rats via PI3K/Akt pathway

A newly identified polysaccharide (PSG-1) has been purified from Ganoderma atrum. The study was to investigate the protective effect of PSG-1 on diabetes-induced endothelial dysfunction in rat aorta. Rats were fed a high fat diet for 8 weeks and then injected with a low dose of streptozotocin to induce type 2 diabetes. The diabetic rats were orally treated with PSG-1 for 4 weeks. It was found that administration of PSG-1 significantly reduced levels of fasting blood glucose, improved endothelium-dependent aortic relaxation, increased levels of phosphoinositide 3-kinase (PI3K), phospho-Akt (p-Akt), endothelial nitric oxide synthase (eNOS) and nitric oxide in the aorta from diabetic rats, compared to un-treated diabetics. These results suggested that the protective effects of PSG-1 against endothelial dysfunction may be related to activation of the PI3K/Akt/eNOS pathway.

Abstract 306: Lipoxin A4 Mediates Aortic Contraction and Endothelial Dysfunction via Reactive Oxygen Species

Lipoxin A4 (LX4) is a biologically active product generated from arachidonic acid by lipoxygenase action and its formation is not inhibited by aspirin. In fact, aspirin triggers the production of lipoxins through acetylation of cyclooxygenase 2 (COX-2) that metabolizes arachidonic acid to 15(R)-hydroxyeicosatetraenoic acid. This metabolite is then converted, via lipoxygenase, to lipoxin, also known as “aspirin-triggered lipoxin”. LX4 has both anti-inflammatory and proinflammatory actions that are related with anaphylaxis, reocclusion and restenosis after coronary angioplasty in patients treated with aspirin. The formation of LX4 within the vascular lumen and wall during inflammation, e.g. after aspirin treatment, places this lipid in a strategically advantageous site for modulation of vascular function. However, little is known of the actions of LX4 on the vasculature. We hypothesized that LX4 would elicit contractile responses and will induce endothelial dysfunction in rat aorta. We used aorta from 12-week old male Wistar rats to assess vascular function on the pin myograph and reactive oxygen species (ROS) production via dihydroethidium fluorescence. LX4 (1-300 nM) induced concentration-dependent contractions and indomethacin, a COX inhibitor (INDO, 10 μM), did not affect this result (E max , LX4: 30±6 vs. INDO: 20±1 % of KCl, p&gt;0.05). Also, concentration-response curves to acetylcholine (ACh, 0.1 nM-30 μM) and phenylephrine (PE, 1 nM-30 μM) were performed in the absence (vehicle) or presence of LX4 (1 nM). LX4 increased aortic sensitivity to PE (pD 2 , vehicle: 7.37±0.05 vs. LX4: 7.64±0.07, p&lt;0.05) and decreased ACh-induced relaxation (E max , vehicle: 86±3 vs. LX4: 67±3 % of PE, p&lt;0.05). Finally, incubation of aortic segments with LX4 (1 nM) for 15 min significantly increased dihydroethidium fluorescence (0.33±0.01 fold compared to vehicle, p&lt;0.05), suggesting that LX4 may induce oxidative stress. In conclusion, these results show that LX4 has a functional role in aorta and may contribute to vascular dysfunction via increases in ROS. This lipid may contribute to further vascular damage in conditions where its production is exacerbated, such as in atherosclerosis or angioplasty-associated complications treated with aspirin.

Nitric Oxide- and Heme-Independent Activation of Soluble Guanylate Cyclase Attenuates Peroxynitrite-Induced Endothelial Dysfunction in Rat Aorta

Oxidative stress interferes with nitric oxide (NO)/soluble guanylate cyclase (sGC)/cyclic guanosine monophosphate (cGMP) signalling pathway through reduction of endogenous NO and formation of the strong intermediate oxidant peroxynitrite and leads to vascular dysfunction. We evaluated the effects of oral treatment with NO- and heme-independent sGC activator cinaciguat on peroxynitrite-induced vascular dysfunction in rat aorta. Sprague-Dawley rats were treated orally 2 times at an interval of 17 hours with vehicle or with cinaciguat (10 mg/kg). One hour after the last treatment, the animals were anesthetized, the thoracic aorta was removed, and the aortic segment preparations were incubated with and without the reactive oxidant peroxynitrite (200 µmol/L, 30 minutes). Endothelium-dependent (acetylcholine), -independent (sodium nitroprusside) vasorelaxations were investigated, and histopathological examination was performed. Incubation of aortic rings with peroxynitrite significantly attenuated the maximal endothelium-dependent relaxation (R (max)) to acetylcholine (peroxynitrite, 44.5% ± 5.9% vs control, 93.2% ± 2.0%, P < .05) and decreased pD(2) values (-logEC(50), EC(50) being the concentration of acetylcholine that elicited 50% of the maximal response) for the concentration-response curves as compared to control segments. Treatment of rats with cinaciguat significantly improved the decreased acetylcholine-induced vasorelaxation after exposure of aortic rings to peroxynitrite (cinaciguat + peroxynitrite, 67.1% ± 3.5% vs peroxynitrite, 44.5% ± 5.9%, P < .05). Incubation of aortic segments with peroxynitrite caused a significant shift of the sodium nitroprusside concentration-response curves to the right without any alterations in the R (max). Moreover, exposure of aortic rings to peroxynitrite resulted in increased nitro-oxidative stress and DNA breakage which were improved by cinaciguat. Treatment of rats with cinaciguat significantly increased intracellular cGMP levels in the aortic wall. Our results show under conditions of nitro-oxidative stress when signalling in the NO/sGC/cGMP pathway is impaired, acute activation of sGC by cinaciguat might be advantageous in the treatment of endothelial dysfunction in cardiovascular disease.

Circulating Microparticles from Pulmonary Hypertensive Rats Induce Endothelial Dysfunction

Pulmonary arterial hypertension (PAH) is a severe disease characterized by an increase of pulmonary vascular resistance, which is accompanied by functional and structural changes in pulmonary arteries. Microparticles (MPs) have been described as biological vector of endothelial dysfunction in other pathologies. The purpose of this work was to characterize circulating MPs during hypoxic PAH and to study their effects on endothelial function. Male Wistar rats were exposed or not to chronic hypoxia, and normoxic or hypoxic MPs from blood were characterized by flow cytometry. Endothelial cells (ECs) from rat aorta or pulmonary arteries were incubated with MPs, and then expression and phosphorylation of enzymes involved in nitric oxide (NO) and reactive oxygen species productions were analyzed. Hypoxic MPs were injected into rats, and endothelium-dependent relaxation was assessed. Circulating levels of MPs from hypoxic rats were twofold higher than those present in normoxic rats. In vitro treatment of ECs with hypoxic MPs reduced NO production in aortas and pulmonary arteries by enhancing phosphorylation of endothelial NO synthase at the inhibitory site. Hypoxic MPs increased oxidative stress only in pulmonary ECs via xanthine oxidase and mitochondrial implication. In vivo injection of hypoxic MPs into rat impaired endothelium-dependent relaxation both in aorta and pulmonary arteries. These data provide evidence that hypoxic circulating MPs induce endothelial dysfunction in rat aorta and pulmonary arteries by decreasing NO production. Moreover, MPs display tissue specificity with respect to increased oxidative stress, which occurs only in pulmonary ECs.

Dietary inhibition of xanthine oxidase attenuates radiation-induced endothelial dysfunction in rat aorta

Radiation exposure is associated with the development of various cardiovascular diseases. Although irradiation is known to cause elevated oxidant stress and chronic inflammation, both of which are detrimental to vascular function, the molecular mechanisms remain incompletely understood. We previously demonstrated that radiation causes endothelial dysfunction and increased vascular stiffness by xanthine oxidase (XO) activation. In this study, we investigated whether dietary inhibition of XO protects against radiation-induced vascular injury. We exposed 4-mo-old rats to a single dose of 0 or 5 Gy gamma radiation. These rats received normal drinking water or water containing 1 mM oxypurinol, an XO inhibitor. We measured XO activity and superoxide production in rat aorta and demonstrated that both were significantly elevated 2 wk after radiation exposure. However, oxypurinol treatment in irradiated rats prevented aortic XO activation and superoxide elevation. We next investigated endothelial function through fluorescent measurement of nitric oxide (NO) and vascular tension dose responses. Radiation reduced endothelium-dependent NO production in rat aorta. Similarly, endothelium-dependent vasorelaxation in the aorta of irradiated rats was significantly attenuated compared with the control group. Dietary XO inhibition maintained NO production at control levels and prevented the development of endothelial dysfunction. Furthermore, pulse wave velocity, a measure of vascular stiffness, increased by 1 day postirradiation and remained elevated 2 wk after irradiation, despite unchanged blood pressures. In oxypurinol-treated rats, pulse wave velocities remained unchanged from baseline throughout the experiment, signifying preserved vascular health. These findings demonstrate that XO inhibition can offer protection from radiation-induced endothelial dysfunction and cardiovascular complications.

3′,4′-Dihydroxyflavonol prevents diabetes-induced endothelial dysfunction in rat aorta

Aims Diabetes increases oxidant stress and impairs endothelium-dependent relaxation. We investigated whether the antioxidant 3′,4′-dihydroxyflavonol (DiOHF) reduces the release of superoxide (O 2 −) and preserves endothelial function in aortae from diabetic rats. Main methods Type-1 diabetes was induced in Sprague–Dawley rats by streptozotocin (STZ) treatment (55 mg/kg i.v.) and vascular reactivity and superoxide generation were assessed in aortic rings using standard organ bath techniques and lucigenin-enhanced chemiluminescence respectively. Key findings Eight weeks after STZ treatment blood glucose was elevated (39.4 ± 0.4 mM) compared to citrate treated control rats (5.5 ± 0.1 mM, P < 0.05) and there was an increased aortic generation of O 2 − (control 670 ± 101, diabetic 1535 ± 249 units/mg dry weight, P < 0.05). In aortic rings acetylcholine (ACh)-induced relaxation was impaired ( R max control 78 ± 2, diabetic 66 ± 3%, P < 0.01) whereas endothelium-independent relaxation to sodium nitroprusside (SNP) was unaffected ( R max control 100 ± 1, diabetic 101 ± 2%). When aortic rings were acutely exposed to DiOHF (10 − 5 M) there was a significant reduction in the detection of O 2 − (control 124 ± 15, diabetic 165 ± 21 units/mg, P < 0.01) and enhanced relaxation to ACh ( R max control 84 ± 3, diabetic 87 ± 3%). Two separate groups of rats (control and diabetic) were treated daily with DiOHF (5 mg/kg i.p.) for 7 days. DiOHF treatment reduced superoxide generation in diabetic aortae (untreated diabetic 1471 ± 358, DiOHF-treated diabetic 580 ± 115 units/mg, P < 0.05) and enhanced acetylcholine-induced relaxation ( R max untreated diabetic 58 ± 5, DiOHF-treated diabetic 71 ± 4%, P < 0.05). Significance DiOHF, acutely in vitro or after 1 week treatment in vivo, reduces oxidant stress and preserves endothelium-dependent relaxation in aortae from diabetic rats.

The dihydropyridine calcium channel blocker benidipine prevents lysophosphatidylcholine-induced endothelial dysfunction in rat aorta

BackgroundLysophosphatidylcholine (LPC), an atherogenic component of oxidized low-density lipoprotein, has been shown to induce the attenuation of endothelium-dependent vascular relaxation. Although benidipine, a dihydropyridine-calcium channel blocker, is known to have endothelial protective effects, the effects of benidipine on LPC-induced endothelial dysfunction remain unknown. We examined the effects of benidipine on the impairment of endothelium-dependent relaxation induced by LPC.MethodsBenidipine was administered orally to rats and aortas were then isolated. Aortic rings were treated with LPC and endothelial functions were then evaluated. Additionally, the effects of benidipine on intracellular calcium concentration ([Ca2+]i) and membrane fluidity altered by LPC in primary cultured rat aortic endothelial cells were examined. [Ca2+]i was measured using the fluorescent calcium indicator fura-2. Membrane fluidity was monitored by measuring fluorescence recovery after photobleaching.ResultsTreatment with LPC impaired endothelial function. Benidipine prevents the impairment of relaxation induced by LPC. Acetylcholine elicited an increase in [Ca2+]i in fura-2 loaded endothelial cells. The increase in [Ca2+]i was suppressed after exposure to LPC. Plasma membrane fluidity increased following incubation with LPC. Benidipine inhibited the LPC-induced increase in membrane fluidity and impairment of increase in [Ca2+]i.ConclusionThese results suggest that benidipine inhibited LPC-induced endothelial dysfunction by maintaining increase in [Ca2+]i. Benidipine possesses membrane stabilization properties in LPC-treated endothelial cells. It is speculated that the preservation of membrane fluidity by benidipine may play a role in the retainment of calcium mobilization. The present findings may provide new insights into the endothelial protective effects of benidipine.

Single exposure gamma-irradiation amplifies xanthine oxidase activity and induces endothelial dysfunction in rat aorta

Irradiation of the heart and vasculature can cause a spectrum of cardiovascular complications, including increased risk of myocardial infarction or coronary heart disease. Although irradiation is implicated in oxidant stress and chronic inflammation, the underlying molecular mechanisms have not been elucidated. We tested the hypothesis that irradiation-initiated upregulation of xanthine oxidase (XO), a primary source of cardiovascular reactive oxygen species, contributes to endothelial dysfunction and increased vascular stiffness. Twenty-two, 3-month-old Sprague-Dawley male rats were gamma-irradiated at the following doses: 0, 50, 160, and 500 cGy. Rats exposed to 500 cGy showed a significant increase in endothelial XO expression and a twofold increase in XO activity, compared to the 0 cGy controls. Endothelial function was investigated ex vivo through vascular tension dose-responses to the endothelial dependent vasodilator, acetylcholine. Endothelial-dependent relaxation in aorta of the 500 cGy exposed rats was significantly attenuated from the control group. Remarkably, specific inhibition of XO with oxypurinol restored the relaxation response to that of the control. Furthermore, these ex vivo results are reflected in vivo through alterations in vascular stiffness, as measured by pulse wave velocity (PWV). As early as 1-day post-exposure, rats exhibited a significant increase in PWV from pre-exposure. The PWV of irradiated rats (50, 160, and 500 cGy) were greater than those of 0 cGy control rats at 1 day, 1 and 2 weeks. The sham and irradiated rats possessed equivalent pre-exposure PWV, with sham showing no change over 2 weeks. Thus, these findings suggest that early upregulation of XO contributes to oxidative stress and endothelial nitro-redox imbalance with resultant endothelial dysfunction and altered vascular mechanics. Furthermore, these data identify XO as a potential molecular target for attenuating irradiation-induced cardiovascular injury.

Protective effects of quercetin and its metabolites on endothelial dysfunction in rat aorta

Epidemiological studies have reported an inverse association between dietary flavonoid intake and mortality for ischemic heart disease. Quercetin is the most abundant flavonoid in the diet, but it is not present in plasma as a free form. The main metabolites of quercetin in human plasma are: quercetin-3-glucuronide, quercetin-3′-sulphate, isorhamnetin-3-glucuronide and 4′-glucuronide. In this study, we have characterised the vascular effects of these conjugates on rat aorta. We found that these metabolites lacked a direct vasodilator effect. Moreover, they did not suffer auto-oxidation, did not generate free radicals, and did not inhibit the biological activity of NO. However, these metabolites protected the biological activity of NO and reversed the endothelial dysfunction induced by an inhibitor of superoxide dismutase or by NADPH-induced NADPH oxidase activation. These data indicate for the first time that the conjugated metabolites could be responsible for the in vivo protective activity of quercetin on endothelial dysfunction and blood pressure. Supported by AGL2004-06685/ALI and SAF2005-03770

Dietary L-Arginine Restores Aspirin-induced Endothelial Dysfunction in Rat Aorta

L-Arginine induced elevation of the vascular prostanoid led us to think that the risk of coronary spasm may increase in L-arginine consumers when they are subjected to cyclooxygenase inhibitors and this limits the therapeutic value of aspirin. So the aim was to investigate the interaction of aspirin and dietary L-arginine in male rats. Animals were divided into four groups and fed with normal food. The first group received tap water while the second, third and fourth groups were subjected daily to aspirin (8.6 mg/kg), L-arginine (143 mg/kg) and aspirin + L-arginine combination in their drinking water respectively for 7 days. Vasomotor responses were recorded in the aortic rings suspended for isometric-force recordings. Aspirin treatment significantly reduced the dilation to acetylcholine and sodium nitroprusside. Attenuated phenylephrine contractility was associated with normal acetylcholine response in L-arginine group. Addition of L-arginine to aspirin treatment completely prevented aspirin-induced endothelial dysfunction but defective response to sodium nitroprusside persisted. Dietary L-arginine without affecting maximal dilation to acetylcholine significantly increased the share of dilator prostanoid which appears to resist aspirin. These results demonstrated that dietary L-arginine increases dilator prostaoid in rat aortic rings. Contrary to our expectation, co-administered L-arginine protected aspirin induced endothelial dysfunction and ruled out the limitation of aspirin use in L-arginine consumers.

Diabetic-induced endothelial dysfunction in rat aorta: role of hydroxyl radicals.

Previous studies suggest a role of superoxide anion radicals (.O2-) in impaired endothelium-dependent relaxation of diabetic blood vessels; however, the role of secondary reactive oxygen species remains unclear. In the present study, we investigated a role of various potential reactive oxygen species in diabetic endothelial dysfunction. Thoracic aortic rings from 8-week streptozotocin-induced diabetic and age-matched control rats were mounted in isolated tissue baths. Endothelium-dependent relaxation to acetylcholine (ACH) and endothelium-independent relaxation to nitroglycerin (NTG) were assessed in precontracted rings. ACH-induced relaxation was impaired in diabetic compared to control rings and was not improved with either indomethacin or daltroban. ACH-induced relaxation in both control and diabetic rings was completely blocked with the nitric oxide synthase inhibitors, L-nitroarginine methyl ester or L-nitroarginine (L-NA). NTG-induced relaxation was insensitive to L-NA and was unaltered by diabetes. Pretreatment with superoxide dismutase (SOD) at activities which did not alter contractile tone failed to alter response to ACH in diabetic rings. Similar results were obtained using either catalase or mannitol. In contrast, the combination of SOD plus catalase or DETAPAC, an inhibitor of metal-facilitated hydroxyl radical (.OH) formation, markedly enhanced relaxation to ACH in diabetic but not in control rings. Neither the combination of SOD plus catalase nor DETAPAC altered the sensitivity or relaxation to NTG in control rings with or without endothelium. In diabetic rings with endothelium, both DETAPAC or SOD plus catalase increased sensitivity but not maximum relaxation to NTG. In diabetic rings without endothelium, relaxation and sensitivity to NTG were unaltered by either treatment. In L-NA-treated diabetic rings with endothelium, sensitivity and relaxation to NTG was unaltered by either DETAPAC or SOD plus catalase. Diabetic endothelium produces increases in both .O2- and H2O2 leading to enhanced intracellular production of .OH. Thus, .OH are implicated in diabetes-induced endothelial dysfunction.