Relaxation Responses Of Aortic Rings Research Articles

The protective role of neuronal nitric oxide synthase in endothelial vasodilation in chronic β-adrenoceptor overstimulation

AimsNitric oxide synthases (NOSs) are key enzymes regulating vascular function. Previously, we reported that β-adrenergic (β-AR) overstimulation, a common feature of cardiovascular diseases, did not impair endothelium-dependent vasodilation, although it resulted in endothelial NOS (eNOS) uncoupling and reduced NO bioavailability. In addition to NO, neuronal NOS (nNOS) produces H2O2, which contributes to vasodilation. However, there is limited information regarding vascular β-AR signaling and nNOS. In the present study, we assessed the possible role of nNOS-derived H2O2 and caveolins on endothelial vasodilation function following β-AR overstimulation. Main methodsMale C57BL/6 wild-type and nNOS knockout mice (nNOS−/−) were treated with the β-AR agonist isoproterenol (ISO, 15 mg·kg−1·day−1, s.c.) or vehicle (VHE) for seven days. Relaxation responses of aortic rings were evaluated using wire myograph and H2O2 by Amplex Red. Key findingsAcetylcholine- or calcium ionophore A23187-induced endothelium-dependent relaxation was similar in aortic rings from VHE and ISO. However, this relaxation was significantly reduced in aortas from ISO compared to VHE when (1) caveolae were disrupted, (2) nNOS was pharmacologically inhibited or genetically suppressed and (3) H2O2 was scavenged. NOS-derived H2O2 production was higher in the aortas of ISO mice than in those of VHE mice. Aortas from ISO-treated mice showed increased expression of caveolin-1, nNOS and catalase, while caveolin-3 expression did not change. SignificanceThe results suggest a role of caveolin-1 and the nNOS/H2O2 vasodilatory pathway in endothelium-dependent relaxation following β-AR overstimulation and reinforce the protective role of nNOS in cardiovascular diseases associated with high adrenergic tone.

Nebivolol suppresses asymmetric dimethylarginine and attenuates cyclosporine-induced nephrotoxicity and endothelial dysfunction in rats.

Cyclosporine A (CsA)-induced nephrotoxicity is a challenging problem complicating its chronic use in a large array of autoimmune diseases, as well as in organ transplantation. A considerable body of evidence points to the involvement of nitric oxide (NO) and its endogenous synthesis inhibitor, asymmetric dimethylarginine (ADMA), in CsA-induced renal and cardiovascular adverse effects. In this study, the potential of the third generation β-blocker, nebivolol, to modify the NO/ADMA system is hypothesized to play a role in protection against CsA-induced renal injury and endothelial dysfunction. Both in vivo and in vitro studies were carried out on 36 male Wistar rats randomly divided into three groups; normal control, CsA (30mg/kg/day)-treated or CsA+nebivolol (30mg/kg and 1mg/kg daily, respectively)-treated groups. After four weeks, blood pressure, lipid profile, renal functions, renal oxidative status, NO, inducible NO synthase and ADMA were assessed. In vitro evaluation of vascular relaxant responses of norepinephrine pre-contracted aortic rings to acetylcholine (ACh) and sodium nitroprusside were evaluated. Concurrent nebivolol treatment significantly attenuated CsA-induced hypertension, impairment of renal functions, oxidative stress and restored the balance in renal NO system with lowering of the elevated ADMA. This was associated with favourable effects on lipid profile. Nebivolol treatment also abrogated the CsA-induced impairment of relaxant responses of aortic rings to ACh. Nebivolol possesses multifaceted actions that make it advantageous to combat the CsA-induced toxic effects on renal and endothelial functions.

D Endothelium specific insulin resistance leads to accelerated atherosclerosis: a role for reactive oxygen species

<h3>Background</h3> Global insulin resistance and endothelial dysfunction have been identified as predisposing factors for atherosclerosis. However, it is unclear whether selective insulin resistance in endothelial cells alone, is sufficient to promote atherosclerosis. We addressed this question by crossing Endothelial Specific Mutant Insulin Receptor Over-expressing (ESMIRO) mice with ApoE^−/− mice. ESMIRO mice over-express a human insulin receptor with an Ala-Thr1134 mutation in the tyrosine kinase domain (which disrupts insulin signalling) selectively in endothelial cells under the control of the tie-2 promoter/enhancer. <h3>Methods</h3> Male ApoE^−/−/ESMIRO mice were compared with sex-matched littermate ApoE^−/− mice (both on a C57Bl6 background) after feeding a Western-style diet for 12 weeks. <h3>Results</h3> ApoE^−/−/ESMIRO mice were morphologically indistinguishable from ApoE^−/− control littermates and showed normal development with no differences between groups in body mass. Heart rate, systolic blood pressure, glucose tolerance, insulin sensitivity and fasting glucose levels were similar in ApoE^−/−/ESMIRO and ApoE^−/− mice. ApoE^−/−/ESMIRO cultured endothelial cells demonstrated insulin resistance through significantly reduced insulin mediated eNOS activity (p=0.003). Aortic lipid deposition along the whole aorta, assessed by en-face oil red O staining, was similar in ApoE^−/−ESMIRO and ApoE^−/− mice (6.4%±0.5% vs 5.8%±0.5%; p=0.39). Analysis of lipid deposition along the lesser curvature of the aortic arch revealed a significant increase in ApoE^−/−ESMIRO when compared to controls (9.4±0.89 vs 12.43±1.19% p=0.035). Atherosclerotic lesion area in cross sections of aortic sinus was also significantly increased in ApoE^−/−/ESMIRO mice compared to ApoE^−/− controls (24.8%±2.4% vs 16.6%±2.4%; p=0.02). Vascular function assessed through relaxation responses of aortic rings in response to the endothelial specific vasodilator acetylcholine revealed that aortic rings from ApoE^−/−/ESMIRO mice had blunted relaxation responses to acetylcholine (Emax ApoE^−/− 102.88±6, Emax ApoE^−/−/ESMIRO 65±41%, p=0.02), which was restored by the superoxide dismutase mimetic and antioxidant MnTMPyP (Emax ApoE^−/−/ESMIRO without MnTMPyP 65±41%, with MnTMPyP 112±15% p=0.048). Endothelial cells from ApoE^−/−/ESMIRO mice had significantly increased basal generation of superoxide (1.87-fold increase compared to ApoE^−/− p&lt;0.05) which was blunted by the selective NADPH oxidase inhibitor gp91ds-tat (11% reduction ±0.02, p=0.03) and the non-selective NO synthase inhibitor L-NMMA (6% reduction ±0.01, p=0.03). <h3>Conclusions</h3> Endothelial specific insulin resistance is sufficient to promote atherosclerosis and increase lesion area in ApoE null mice potentially via the increased ROS displayed in this model. This suggests that enhancing endothelial insulin sensitivity may be an appropriate target to prevent atherosclerosis in insulin-resistant conditions.

DIRECT EFFECTS OF QUERCETIN ON IMPAIRED REACTIVITY OF SPONTANEOUSLY HYPERTENSIVE RAT AORTAE: COMPARATIVE STUDY WITH ASCORBIC ACID

1. There is a growing interest in the anti-oxidant characteristics and use of flavonoids in the management of cardiovascular diseases. The cardiovascular mechanism of action of these plant derivatives remains controversial. This study compared the effects of the flavonoid quercetin with those of the anti-oxidant vitamin ascorbic acid (vitamin C) on the reactivity of aortic rings from spontaneously hypertensive rats (SHR). 2. The phenylephrine (PE)-induced contractile and the endothelium-dependent and independent relaxant responses of aortic rings from 21 to 22 week old SHR and age-matched normotensive Wistar (WKY) rats were observed in the presence of quercetin or ascorbic acid. All the experiments were performed in the presence of the cyclooxygenase inhibitor, indomethacin (10 micromol/L). 3. The endothelium-dependent and independent relaxations to acetylcholine (ACh) and sodium nitroprusside (SNP), respectively, were significantly lesser in the SHR compared to the WKY tissues whereas the contractile responses to PE were similar in both tissues. Pretreatment of WKY rings with quercetin or ascorbic acid had no effect on the responses to ACh or PE. In the SHR tissues, however, quercetin or ascorbic acid significantly improved the relaxation responses to ACh and reduced the contractions to PE with greater potency for quercetin. Both compounds lacked any effects on the responses to SNP in either aortic ring types. N(omega)-nitro-L-arginine methyl ester (l-NAME, 10 micromol/L) significantly attenuated the vasodepressor effects of quercetin and ascorbic acid, raising the responses to PE to a level similar to that observed in the control SHR tissues. In l-NAME pretreated aortic rings, quercetin and ascorbic acid inhibited the contractile responses to PE with the same magnitude in WKY and SHR tissues. 4. The present results suggest that acute exposure to quercetin improves endothelium-dependent relaxation and reduces the contractile responses of hypertensive aortae with a greater potency than ascorbic acid. This suggests a better vascular protection with this flavonoid than ascorbic acid in the SHR model of hypertension and possibly in human cardiovascular diseases.

Inosine reduces systemic inflammation and improves survival in septic shock induced by cecal ligation and puncture.

Inosine is a naturally occurring purine formed from the breakdown of adenosine. Here we have evaluated the effects of inosine in a murine model of polymicrobial sepsis induced by cecal ligation and puncture (CLP). Mice subjected to CLP were treated with either inosine (100 mg/kg, intraperitoneally) or vehicle 1 h before and 6 h after CLP. After 12 h tumor necrosis factor alpha, interleukin 6 (IL-6), and IL-10 were measured in plasma. Biochemical markers of organ damage, liver NAD+/NADH (indicator of the mitochondrial redox state), plasma nitrate, tissue myeloperoxidase (MPO, indicator of neutrophil accumulation) and malondialdehyde (MDA, indicator of lipid peroxidation), liver and lung chemokines (macrophage inflammatory protein 1alpha [MIP-1alpha] and MIP-2), and ex vivo vascular reactivity in aortic rings were also measured. Mice treated with inosine had significantly lower levels of circulating cytokines. Organ damage was significantly reduced by inosine treatment, which was associated at the tissue level with an increased hepatic NAD+/NADH ratio, decreased MPO activity in the lung, reduced MDA formation in the gut and liver, and decreased MIP-1alpha and MIP-2 in the lung and liver. Furthermore, inosine significantly improved endothelium-dependent relaxant responses of aortic rings. These effects were associated with significant improvement of the survival of CLP mice treated with inosine, an effect that was still observed when inosine treatment was delayed 1 h after CLP, especially when it was associated with appropriate antibiotic treatment. Thus, inosine reduced systemic inflammation, organ damage, tissue dysoxia, and vascular dysfunction, resulting in improved survival in septic shock.

Relaxation responses of aortic rings from salt-loaded high calcium fed rats to potassium chloride, calcium chloride and magnesium sulphate

Abstract The relaxation responses of aortic rings of rats fed either normal rat feed, 8% salt diet, 8% salt+2.5% Ca diet or 2.5% Ca diet for 6–8 weeks has been investigated. The mean arterial pressure of salt loaded rats (148.63±8.54 mmHg) was higher ( P P 2 ( P P −1 significantly ( P 4 in aortic rings from all the groups. The result of this study indicates that salt-loading caused significant increase in the blood pressure of the rats and also reduced the relaxation responses of the aortic rings to KCl, MgSO 4 and CaCl 2 which suggest altered Na + ,K + -ATPase activity and resistance of the vascular smooth muscle membrane to calcium-induced membrane stabilization. These defects were reversed by dietary calcium supplement.

Changes in noradrenaline sensitivity and morphology of arterial resistance vessels during development of high blood pressure in spontaneously hypertensive rats.

Changes in noradrenaline sensitivity and morphology of arterial resistance vessels during development of high blood pressure in spontaneously hypertensive rats.