Alterations In Vascular Reactivity Research Articles

Aging and total stenosis triggers differential responses of carotid and basilar arteries to endothelin-1 and phenylephrine

Our aim was to investigate the effects of ageing on the vascular contractility of carotid and basilar arteries from guinea-pigs, in a model of total stenosis. Moreover, we attempted to identify whether total stenosis of the left common carotid (stenosed) in adult guinea-pigs, would affect the contractions of contralateral carotid (intact) and basilar arteries to different vasoconstrictors. With this purpose, the left carotid was occluded with a silk thread at a position close to its origin. Vascular reactivity experiments using standard muscle bath were performed 7, 15, 30, and 90 days after carotid occlusion. Reactivity of carotid and basilar arteries to endothelin-1, phenylephrine and KCl was reduced with ageing in naive guinea-pigs. The endothelin-1 and KCl-induced contractions were unaltered in arteries from SHAM-operated animals. Moreover, phenylephrine-induced contractions were reduced in both carotids from 7 days SHAM-operated guinea-pigs, when compared to naive group. Stenosis induced progressive reduction in the contraction induced by endothelin-1, phenylephrine and KCl in the stenosed carotid, when compared to their respective age-matched naive and SHAM groups. Interestingly, an increased contractile-response to vasoconstrictor agents in all the contralateral carotids was observed. Stenosis (30 and 90 days) also induced an increase in the contractions induced by endothelin-1 in the basilar artery. Conversely, phenylephrine and KCl-induced contractions were reduced in basilar arteries 7, 15, 30 and 90 days after stenosis. These results showed that stenosis in adult guinea-pigs induce alterations of vascular reactivity in arteries distant from the site of injury. Thus, in spite of the common use of contralateral carotid as control, it must be aware of the potential alteration induced by stenosis in the vascular motility of such vessels. Additionally, it was verified a relationship between the period of stenosis and the alterations in the vascular reactivity to these vasoconstrictors.

Mechanisms of Aortic and Cardiac Dysfunction in Uremic Mice With Aortic Calcification

Chronic renal failure (CRF) is associated with cardiac dysfunction and increased aortic stiffness. The mechanisms involved are not clearly understood. We examined changes over time in cardiac and aortic function in a murine CRF model. Eight-week-old mice were randomly assigned to 1 of 4 groups: wild-type non-CRF, wild-type CRF, apolipoprotein E knockout non-CRF, and apolipoprotein E knockout CRF. Echocardiography was performed and blood samples were taken at baseline and after 6 and 10 weeks of CRF. Vascular reactivity and adhesion molecule expression were studied after 6 and 10 weeks of CRF. Left ventricular hypertrophy, altered left ventricular relaxation, and increased aortic stiffness were observed after 6 weeks of CRF and persisted after 10 weeks. The 4 groups of mice did not significantly differ in terms of arterial blood pressure and aortic structure. The degree of vascular calcification and serum total cholesterol concentration were higher in the CRF groups than in the non-CRF groups. These changes, however, could not explain the cardiac and vascular differences seen in the 2 CRF groups. In contrast, alterations in vascular reactivity, the upregulation of adhesion molecule expression, and CRF status were significantly associated with these changes. In a mouse model of CRF, left ventricular hypertrophy, cardiac diastolic dysfunction, and increased aortic stiffness were not related to structural changes in the aorta (including aortic calcification) or high serum cholesterol levels. However, cardiac and aortic abnormalities were associated with the extent of subendothelial dysfunction and the severity of CRF.

Phytosterols: to be or not to be toxic; that is the question

Plant sterols (phytosterols) are membrane constituents of all plants with a structure analogous to that of cholesterol. Thus, phytosterols have either an additional methyl or ethyl group on the carbon-24 position or an additional double bond in the side chain (1) . Noteworthy, in patients with the rare inherited disease of phytosterolaemia characterized by a hyperabsorption and diminished biliary secretion of cholesterol and phytosterols as well as by tendon and tuberous xanthoma, elevated plasma concentrations of phytosterols (campesterol, sitosterol) have been shown to constitute a risk factor for premature atherosclerosis (2) . However, whether plasma concentrations of campesterol and sitosterol are risk factors for CVD in subjects without phytosterolaemia is not clearly established, and still remains controversial (3) . Thus, whereas some benefits are attributed to phytosterols found in fruits, vegetables, vegetable oils, seeds and nuts (4) , especially their ability in decreasing cholesterol concentrations through various ATP-binding cassette transporters present at the intestinal level (5,6) , the potential effects of phytosterols, and of their oxide derivatives (7) , on other metabolic processes remain to be elucidated (8) . Therefore, the article by Rubis et al. (9) , published in the current issue of the British Journal of Nutrition, concerning the in vitro effects of rape seed oil extract components (a mixture of various phytosterols containing mainly campesterol, sitosterol and stigmasterol derivatives), of b-sitosterol, and of 5a,6a-epoxycholesterol on the proliferation and viability of the human abdominal aorta endothelial cells, HAAE-2, is of great interest. In agreement, with previous investigations (10) , strong cytotoxic effects of b-sitosterol were shown, whereas a low cytotoxicity and no side-effects were observed with 5a,6a-epoxycholesterol and the seed oil extract, respectively. Although absorption of plant sterols is low compared with cholesterol (11) , these data show that some phytosterols, in isolation, can have more or less pronounced cytotoxic effects on normal cells. These observations are in agreement with those obtained with high concentrations of b-sitosterol (up to 0·7 mM) on human umbilical vein endothelial cells where cell contraction and increased release of intracellular lactate dehydrogenase in the culture medium was reported (12) . Interestingly, these observations suggest that very high concentrations of certain phytosterols (mainly b-sitosterol) in foodstuffs might impair vascular reactivity, and interfere with the vascular tone. As it has been well established (1) that atherosclerosis is associated with abnormalities of vascular function characterized both by an increase in the response to specific vasoconstrictor agents (13) , and by a marked attenuation of endothelium-dependent relaxation (14) , and (2) that alteration of vascular reactivity occurs at an early stage of the atherosclerotic process (13,15) , it seems very important to identify precisely the effects of certain phytosterols on the endothelium. However, only concentrations of the oil extract that contain high, non-physiological concentrations of b-sitosterols resulted in a significant growth inhibition. Therefore, as previously reported and as well described with oxysterol mixtures (16) , these data indicate that some phytosterols may quench the inherent toxic effects of others, and may therefore counteract the proatherogenic signals involved in the initiation and the development of atherosclerotic lesions. Thus, as the involvement of phytosterols in atherogenesis cannot be excluded, a better knowledge of the biological activities of these molecules present in high amounts in various foodstuffs remains an important and essential source of investigation necessary to avoid important side-effects, and to identify adequate phytosterol mixtures capable of bringing benefit to human health.

Fenofibrate and Pioglitazone Do Not Ameliorate the Altered Vascular Reactivity in Aorta of Isoproterenol-treated Rats

Chronic stimulation of beta-adrenoceptors with isoproterenol induces alteration of vascular reactivity and increases local pro-inflammatory cytokines. We investigated whether fenofibrate and pioglitazone, PPAR-alpha and -gamma agonists, respectively, improve the changes in vascular reactivity induced by isoproterenol. Wistar rats received isoproterenol (0.3 mg x kg x day, SC) or vehicle (CT) plus fenofibrate (alpha, 100 mg x kg x day, PO), pioglitazone (gamma, 2.5 mg.kg.day, PO), or water for 7 days. In aortas, isoproterenol treatment enhanced the maximal response (Rmax) to phenylephrine (10 to 10 M) compared to CT as previously demonstrated. The effects of endothelium removal (E-) or L-NAME incubation (100 microM) on the phenylephrine response were smaller in isoproterenol-treated animals compared to CT while superoxide dismutase (SOD, 150 U/mL) significantly reduced the Rmax to phenylephrine to CT levels. Neither fenofibrate nor pioglitazone changed the effects induced by isoproterenol in aorta. E-, L-NAME, or SOD effects were similar between CTalpha and CT. However, pioglitazone per se increased Rmax to phenylephrine (CT: 59 +/- 4 versus CTgamma: 72 +/- 5 % of contraction to KCl). E- or L-NAME effects were reduced in CTgamma compared to CT, and SOD normalized the altered reactivity to phenylephrine in the CTgamma group. In conclusion, neither fenofibrate nor pioglitazone ameliorates the altered vascular reactivity present in aorta from isoproterenol-treated rats. Moreover, pioglitazone per se induced endothelial dysfunction and increased phenylephrine-induced contraction in aorta.

Diminished NO generation by injured endothelium and loss of macula densa nNOS may contribute to sustained acute kidney injury after ischemia-reperfusion

In postischemic acute kidney injury (AKI) or acute renal failure, a dissipation of glomerular filtration pressure is associated with an altered renal vascular tone and reactivity, as well as a loss of vascular autoregulation. To test the hypothesis that renal nitric oxide (NO) generation reflects endothelial damage in the kidney after ischemia-reperfusion, we quantified the urinary NO levels and identified the site of its generation in postischemic AKI. Subjects were 50 recipients of cadaveric renal allografts: 15 with sustained AKI and 35 with recovering renal function. Urine and blood samples were obtained after transplant, and intraoperative allograft biopsies were performed to examine NO synthases (NOSs) in the kidney. In the sustained AKI group, urinary nitrite and nitrate excretion (in mumol/g urine creatinine) was lower (12.3 +/- 1.8 and 10.0 +/- 1.4 on postoperative days 0 and 3) than in the recovery group [20.0 +/- 3.6 and 35.1 +/- 5.3 (P < 0.005 vs. sustained AKI on days 0 and 3) on postoperative days 0 and 3]. Endothelial NOS expression diminished from the peritubular capillaries of 6 of 7 subjects in the sustained AKI group but from only 6 of 16 subjects in the recovery group. No differences were observed in the inducible NOS staining pattern between the two groups. Neuronal NOS staining was rarely observed in the macula densae of subjects but was prominent in control tissues. These findings suggest that a diminished NO generation by injured endothelium and loss of macula densa neuronal NOS could impair the vasodilatory ability of the renal vasculature and contribute to the reduction in the glomerular filtration rate in postischemic AKI.

Adenosine-mediated alteration of vascular reactivity and inflammation in a murine model of asthma

Chronic respiratory disorders such as asthma are believed to be associated with adverse cardiovascular events. We hypothesize that asthmatic inflammation translates into systemic inflammation and alters vascular responses where adenosine (AD) plays an important role. Therefore, this study investigated the effects of aerosolized AD, used to elevate lung AD levels, on vascular reactivity and inflammation in our allergic mouse model of asthma. Balb/c mice were divided into four groups: control (Con), Con + aerosolized AD (Con + AD), allergen sensitized and challenged (Sen), and Sen + aerosolized AD (Sen + AD). The animals were sensitized with ragweed (200 mug ip) on days 1 and 6, followed by 1% ragweed aerosol challenges from days 11 to 13. On day 14, the Con + AD and Sen + AD groups received a single AD aerosol challenge (6 mg/ml) for 2 min, followed by the collection of the aorta and plasma on day 15. Organ bath experiments showed concentration-dependent aortic relaxations to AD in the Con and Con + AD groups, which were impaired in the Sen and Sen + AD groups. Real-time PCR data showed changes in aortic AD receptors (ARs), with the expression of A(1)ARs upregulated, whereas the expression of A(2)ARs and endothelial nitric oxide synthase genes were downregulated, resulting in an impairment of vasorelaxation in the Sen and Sen + AD groups. The A(1)AR antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) reversed the impairment in vasorelaxation observed in the Sen and Sen + AD groups, whereas the A(2B)AR antagonist alloxazine inhibited vasorelaxation in all groups. Allergen challenge caused systemic inflammation in allergic mice, with AD aerosol further enhancing it as determined by the inflammatory cytokines profile in plasma. In conclusion, asthmatic mice showed altered vascular reactivity and systemic inflammation, with AD aerosol further exacerbating these effects.

Transient receptor potential melastatin 6 and 7 channels, magnesium transport, and vascular biology: implications in hypertension

Magnesium, an essential intracellular cation, is critically involved in many biochemical reactions involved in the regulation of vascular tone and integrity. Decreased magnesium concentration has been implicated in altered vascular reactivity, endothelial dysfunction, vascular inflammation, and structural remodeling, processes important in vascular changes and target organ damage associated with hypertension. Until recently, very little was known about mechanisms regulating cellular magnesium homeostasis, and processes controlling transmembrane magnesium transport had been demonstrated only at the functional level. Two cation channels of the transient receptor potential melastatin (TRPM) cation channel family have now been identified as magnesium transporters, TRPM6 and TRPM7. These unique proteins, termed chanzymes because they possess a channel and a kinase domain, are differentially expressed, with TRPM6 being found primarily in epithelial cells and TRPM7 occurring ubiquitously. Vascular TRPM7 is modulated by vasoactive agents, pressure, stretch, and osmotic changes and may be a novel mechanotransducer. In addition to its magnesium transporter function, TRPM7 has been implicated as a signaling kinase involved in vascular smooth muscle cell growth, apoptosis, adhesion, contraction, cytoskeletal organization, and migration, important processes involved in vascular remodeling associated with hypertension and other vascular diseases. Emerging evidence suggests that vascular TRPM7 function may be altered in hypertension. This review discusses the importance of magnesium in vascular biology and implications in hypertension and highlights the transport systems, particularly TRPM6 and TRPM7, which may play a role in the control of vascular magnesium homeostasis. Since the recent identification and characterization of Mg2+-selective transporters, there has been enormous interest in the field. However, there is still a paucity of information, and much research is needed to clarify the exact mechanisms of magnesium regulation in the cardiovascular system and the implications of aberrant transmembrane magnesium transport in the pathogenesis of hypertension and other vascular diseases.

Altered Potassium Channel Expression in the Human Placental Vasculature of Pregnancies Complicated by Fetal Growth Restriction

Objective: Decreased activity of “oxygen-sensitive” potassium (K) channels reduces hypoxia-induced contraction of pulmonary vascular tissue. “Oxygen-sensitive” channels are present in the fetoplacental vasculature, where vascular resistance is thought to increase in fetal growth restriction (FGR). We assessed placental gene expression of KV2.1, KV9.3 and KIR6.1, three “oxygen-sensitive” K channels in normal pregnancy and FGR. Methods: Biopsies were obtained from 12 normal pregnancies and 12 pregnancies complicated by FGR. Chorionic plate arteries and veins were dissected from the biopsies and a sample of placental tissue comprising chorionic plate and villus tissue was also collected. All samples were processed and analyzed using “real time” quantitative RT-PCR. Results: KV2.1 and KV9.3 gene expression, in veins and placental homogenate, respectively, were increased in FGR. KIR6.1 gene expression was comparable in normal pregnancy and FGR samples. Conclusions: The gene expression of two voltage-gated K channels thought to be important for altered vascular reactivity following changes in oxygenation is increased in FGR.

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.

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.

Fetal Alcohol Exposure Alters Cerebrovascular Reactivity to Vasoactive Intestinal Peptide in Adult Sheep

Chronic fetal alcohol exposure impairs neural and vascular development. We have previously shown that fetal alcohol exposure is associated with attenuated hypoxic cerebral vasodilation and reduced neuronal vasoactive intestinal peptide (VIP) expression in fetal sheep. In the present study, we tested the hypothesis that fetal alcohol exposure alters vascular development, leading to altered cerebral vascular reactivity to VIP in adulthood. Penetrating intracerebral arterioles were harvested from the brains of adult (10–13 months old) offspring of ewes that had received intravenous infusions of alcohol (1.5 g/kg) or same-volume saline (90 min/day, 5 days/week) during days 30–82 of gestation (full term = 145 days). The isolated arterioles were cannulated with a micropipette system that allowed luminal perfusion and control of luminal pressure and developed spontaneous tone at 40°C and 60 mm Hg luminal pressure. There was no difference in myogenic tone between arterioles exposed prenatally to alcohol (n = 18) and saline controls (n = 17). However, fetal alcohol exposure significantly (p = 0.03) enhanced the dilator responses of adult intracerebral arterioles to VIP [0.1 nM to 1 µM, logEC₅₀: –8.6 ± 0.2 (alcohol) vs. –7.4 ± 0.8 (saline)]. In contrast, there was no difference in dilator responses to H⁺ (pH 6.8 buffer), to adenosine (10 nM to 0.1 mM), or to CGS21680 (an adenosine A_2A receptor agonist, 0.01 nM to 10 µM). Thus, fetal alcohol exposure alters vasomotor sensitivity to VIP in adult intracerebral arterioles – perhaps a compensatory response to alcohol-induced underdevelopment of neurotransmitter pathways involved in cerebral vascular regulation.

Altered Penile Vascular Reactivity and Erection in the Zucker Obese-Diabetic Rat

The combination of the independent risk factors for erectile dysfunction, obesity, hypertension, and diabetes are manifested collectively in a condition known as metabolic syndrome X. However, the exact mechanism(s) by which the combination of these factors contributes to erectile dysfunction have yet to be elucidated. We hypothesized that protein kinase C (PKC) and Rho-kinase enhanced vascular tone and thus contributed to erectile dysfunction in this condition. Erectile function was evaluated by recording voltage-dependent increases in intracavernosal pressure following stimulation of the cavernosal nerve in 16- to 20-week-old lean and obese-diabetic Zucker rats. Cavernosal tissue contractile and relaxation responses were evaluated in vitro when contracted with phenylephrine, endothelin-1 and relaxed by Rho-kinase, PKC inhibitors or sodium nitroprusside. Additionally, cavernosal tissue Rho-kinase, protein kinase, and nitric oxide synthase isoform expression were evaluated by Western blot. The voltage-dependent erectile responses were suppressed by >30% in the obese-diabetic Zucker rat. The maximal stress generated by cavernosal tissue from the obese-diabetic was significantly greater than the lean response by greater than 0.8 mN/mm(2) for both phenylephrine and endothelin stimulation. The PKC inhibitor, chelerythrine, inhibited more than 30% of the phenylephrine-induced and 70% of the endothelin-1-induced contractions. Rho-kinase inhibition, with either Y-27632 or HA-1077, revealed impaired relaxations of nearly 30% in tissue from obese-diabetic animals. Western blot analysis revealed increased protein expression of PKC alpha and delta and Rho-kinase alpha and beta but no loss for endothelial or neuronal nitric oxide synthase. In this rodent model both PKC and Rho-kinase signaling elements may contribute to an enhanced vasoconstriction state of the penile smooth muscle that was differentially dependent on the agonist used. The enhanced vasoconstrictive state of the tissue could contribute to the reduced voltage-dependent erectile response in the obese-diabetic Zucker rat.

Time-dependent effects of hyperoxia on the BOLD fMRI signal in primate visual cortex and LGN

Hyperoxia is present in many anaesthesia protocols used in animal blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) studies. However, little data exist on the influence of hyperoxia on the magnitude of stimulus-induced relative changes in BOLD fMRI signal (ΔBOLD%). No study to date has investigated these effects in a time-resolved manner, although cerebral vasoregulation offers sites for a time-dependent interaction of hyperoxia and ΔBOLD%. Here we investigated time-dependent effects of an inspiratory oxygen fraction of 90%. We tightly clamped end tidal CO2 and body temperature and recorded physiological parameters relevant to rCBF in (fentanyl/isoflurane) anaesthetized monkeys while using visual stimulation to elicit ΔBOLD%. To clarify whether changes in ΔBOLD% arose from changes in baseline blood oxygenation or rather altered neuronal or vascular reactivity, we directly measured changes in rCBV using monocrystalline ion oxide nanoparticles (MION) as contrast agent. In visual cortex we found a biphasic modulation of stimulus-induced ΔBOLD% under hyperoxia: We observed first a significant decrease in ΔBOLD% by −24% for data averaged over the time interval of 0–180 min post onset of hyperoxia followed by a subsequent recovery to baseline. rCBV response amplitudes were decreased by 21% in the same time interval (0–180 min). In the LGN, we neither found a significant modulation of ΔBOLD% nor of MION response amplitude. The cerebrovascular effects of hyperoxia may, therefore, be regionally specific and cannot be explained by a deoxyhemoglobin dilution model accounting for plasma oxygenation without assuming altered neuronal activity or altered neurovascular coupling.

Presence of endothelium prevents contraction induced by phenylephrine (PHE) in aorta from Wistar Audiogenic Rats (WARs) when the sarcoplasmic Ca2+‐ATPase (SERCA) is inhibited.

Doretto et al, (Behavior Genetics, 33:–42, 2003) developed an audiogenic seizure susceptible strain (WARs). Seizures are often associated to cardiovascular alterations. In order to understand alterations in vascular reactivity in WARs submitted to acoustic stimulation, we have studied Ca2+ pumping by SERCA and the contraction stimulated with PHE in aorta rings in the absence (E−) and in the presence of endothelium (E+). Startle induced by acoustic pulses was intercalated 24 h between acute and chronic acoustic stimuli, the latter to test audiogenic seizures. Aorta rings were isolated from acoustically stimulated male Wistar and WARs and placed into bath chambers with Krebs Salt Solution (KSS). Contraction induced by 0.3 μM PHE was higher in WARs E− (2.8±0.3g) than in WARs E+ (0.86±0.1g) or in Wistar (E− 1.4±0.02g or E+ 1.6±0.4g). After 10 min in zero-Ca2+, contraction induced by PHE was abolished in aorta from all groups, except in Wistar E− (0.6±0.01g). Ca2+addition in presence of PHE did not produce contraction in all groups. Thapsigargin (1μM-TG) in Ca2+-free medium did not produce contraction in any group. When Ca2+ solution was added, in presence of TG, only aorta from Wistar rats contracted (E− 0.5±0.01g; E+ 0.5±0.2g). Contraction induced by PHE in Ca2+ solution plus TG, did not recover only in WARs E+ (0.3±0.06g). In conclusion, the presence of endothelium prevents the contraction induced by PHE in aorta from acoustically stimulated WARs after SERCA inhibition. Demonstration that this response is endogenous to WARs will be investigated. Support: FAPESP, CNPq, PROAP-CAPES

Compromised Aortic Vasoreactivity in Male Estrogen Receptor-α-Deficient Mice during Acute Lipopolysaccharide-Induced Inflammation

Activation of the estrogen receptor-alpha (ERalpha) mediates the vasculoprotective effects of estrogen, in part, through modulating nitric oxide (NO) production and vasodilation. Whereas inflammation is accompanied by altered vascular reactivity and underlies the pathogenesis of vascular disease, the role of the ERalpha in the vascular responses associated with acute systemic inflammation remains poorly characterized. Contractile and relaxation responses of isolated aortic segments were investigated 12 h after ip injection of saline or lipopolysaccharide (LPS, 10 mg/kg) in male wild-type (ERalpha(+/+)) and ERalpha-deficient (ERalpha(-/-)) mice. As previously observed, LPS-injected ERalpha(+/+) mice displayed reduced contractile responses to phenylephrine and enhanced vasodilation in response to acetylcholine. In contrast, aortic tissues from LPS-injected ERalpha(-/-) mice displayed enhanced contractile responses and reduced sensitivity to acetylcholine- and sodium nitroprusside-induced vasodilation. LPS treatment in ERalpha(+/+) and ERalpha(-/-) mice resulted in similar increased levels of systemic NO production and inducible NO synthase expression in the vascular wall. However, expression of mRNA and protein for endothelial NOS and soluble guanylate cyclase (alpha- and beta-subunits) were significantly reduced in aortic tissues from LPS-treated ERalpha(-/-) animals, possibly accounting for reduced endothelial NO production and reduced smooth muscle responses to NO. These findings represent new evidence of the functional role of ERalpha in the male vasculature and suggest that during acute LPS-induced inflammatory responses, the ERalpha mediates the sustained expression of the molecular machinery essential for endothelial NO synthesis (i.e. endothelial NOS) and the vascular responses to NO (i.e. soluble guanylate cyclase).

Vitamin E supplementation reverses renal altered vascular reactivity in chronic bile duct-ligated rats

An altered vascular reactivity is an important manifestation of the hemodynamic and renal dysfunction during liver cirrhosis. Oxidative stress-derived substances and nitric oxide (NO) have been shown to be involved in those alterations. In fact, both can affect vascular contractile function, directly or by influencing intracellular signaling pathways. Nevertheless, it is unknown whether oxidative stress contributes to the impaired systemic and renal vascular reactivity observed in cirrhosis. To test this, we evaluated the effect of vitamin E supplementation (5,000 IU/kg diet) on the vasoconstrictor and vasodilator responses of isolated perfused kidneys and aortic rings of rats with cirrhosis induced by bile duct ligation (BDL), and on the expression of renal and aortic phospho-extracellular regulated kinase 1/2 (p-ERK1/2). BDL induced a blunted renal vascular response to phenylephrine and ACh, while BDL aortic rings responded less to phenylephrine but normally to ACh. Cirrhotic rats had higher levels of oxidative stress-derived substances [measured as thiobarbituric acid-reactive substances (TBARS)] and NO (measured as urinary nitrite excretion) than controls. Vitamin E supplementation normalized the renal hyporesponse to phenylephrine and ACh in BDL, although failed to modify it in aortic rings. Furthermore, vitamin E decreased levels of TBARS, increased levels of NO, and normalized the increased kidney expression of p-ERK1/2 of the BDL rats. In conclusion, BDL rats showed a blunted vascular reactivity to phenylephrine and ACh, more pronounced in the kidney and reversed by vitamin E pretreatment, suggesting a role for oxidative stress in those abnormalities.

Carotid arterial stiffness, elastic fibre network and vasoreactivity in semicarbazide-sensitive amine-oxidase null mouse

We examined the arterial phenotype of semicarbazide-sensitive amine-oxidase null mouse (SSAO -/-) using various techniques including high resolution echotracking. SSAO -/- mice showed no change in arterial pressure under anesthesia. The in vivo arterial diameter, only measured in the carotid artery (CA), was higher in SSAO -/- than in SSAO +/+ animals. Elastic modulus-wall stress curves and CA rupture pressure were similar between SSAO -/- and +/+ mice, indicating no change in arterial wall stiffness or mechanical strength. There was no significant difference in insoluble elastin, total collagen content and elastic lamellar morphology between the two genotypes. No alteration in vascular reactivity was observed in aortic rings and mesenteric arteries from SSAO -/- mice. Aortic lysyl oxidase (LO) activity remained unaltered, indicating that SSAO invalidation is not accompanied by a compensatory increase in LO activity. This is the first functional study of arteries lacking SSAO. Our results indicate that SSAO -/- mice present an increased arterial diameter associated with normal arterial mechanical properties, suggesting that SSAO deficiency might contribute to arterial wall remodeling. However, these results argue against the hypothesis that SSAO intervenes in elastic fibre organization, elastin cross-linking processes and vasoreactivity.

Homocysteine-induced changes in vascular reactivity of guinea-pig pulmonary arteries: Role of the oxidative stress and poly (ADP-ribose) polymerase activation

This study was aimed to examine the effects of homocysteine (Hcy) on vascular responsiveness of guinea-pig isolated pulmonary arteries and to investigate possible underlying mechanisms. In order to evaluate vascular reactivity, isometric tension studies were performed in response to potassium chloride (KCl), phenylephrine (Phe), acetylcholine (ACh), and sodium nitroprusside (SNP). Incubation of pulmonary artery rings with Hcy (10 −3 M, 180 min) resulted in significant inhibition of response to ACh (an endothelium-dependent vasodilator)( E max: 55.3±6.7 vs. 13.1±2.0 *, P<0.05) while SNP (an endothelium-independent vasodilator)-induced relaxation was not changed significantly. Furthermore, Hcy enhanced KCl- and Phe-induced contraction of pulmonary artery rings ( E max: 1568±81 vs. 2101±145 * mg for KCl and 1081±101 vs. 1544±117 * mg for Phe, P<0.05). Pulmonary artery ring contractions induced by stepwise addition to Ca 2+ to high KCl solution with no Ca 2+ were also significantly augmented by Hcy incubation ( E max: 1750±121 vs. 2295±134 * mg, P<0.05). To investigate mechanisms of Hcy action, additional sets of experiments involving rings incubation with Hcy alone or with addition of Tiron (an intracellular superoxide anion scavenger, 10 −2 M), PJ34 (an inhibitor of polyADP-ribose polymerase, 3×10 −6 M), and combination of two antioxidant enzymes superoxide dismutase (SOD, 100 U/ml) and catalase (CAT, 120 U/ml) for 180 min. The findings of our study clearly show that all these co-treatments significantly prevented the development of endothelial dysfunction induced by Hcy. Furthermore, the effect of Hcy on KCl- and Phe-induced contraction was significantly inhibited by the concomitant incubation with either SOD plus CAT, Tiron or PJ34. This study demonstrates that Hcy causes a significant alteration in vascular reactivity of pulmonary arteries, and this alteration seems to be via oxidative stress in pulmonary artery endothelium with subsequent DNA damage and activation of poly(ADP-ribose) polymerase (PARP) pathway.

Chronic exercise does not prevent hypoxia-induced increased aortic sensitivity to endothelin in rats

Objectives We report in the present study the effect of regular exercise on vascular reactivity alterations to endothelin (ET-1) following prolonged exposure to hypoxic stress. Methods Male Dark Agouti rats were randomly assigned to N (sedentary rats), NCE (normoxic exercised rats), CH (chronic hypoxic sedentary rats) and CHCE (chronic hypoxic exercised rats) groups. The effects of ET-1 in the presence or not of the endothelium and/or of the specific inhibitor, bosentan, have been investigated in an isolated model of rat thoracic aorta. Results Prolonged exposure to hypoxia induced a significant increase in aortic sensitivity to ET-1 (− log ED 50 in CH = 8.15 ± 0.01 vs in N = 7.98 ± 0.02, p < 0.05). Despite exercise training reduced the sensitivity to ET-1 in normoxic rats, it has no effects in hypoxic rats (− log ED 50 in CH = 8.15 ± 0.01 vs in CHCE = 8.19 ± 0.01, NS). Moreover, although the removal of endothelium has no effect in N rats, it leads, in NCE rats, to a significant increase in sensitivity to ET-1 (− log ED 50 in endothelium intact rings = 7.89 ± 0.04 vs in denuded rings = 8.04 ± 0.02, p < 0.05). The implication of ET-1 receptors on both endothelial and smooth muscle cells is confirmed by the significant reduced sensitivity to ET-1 in the four groups when bosentan is present in organ bath. Conclusion Our study clearly suggests that part of the beneficial effect of chronic exercise could be mediated by enhancing endothelial function associated with endothelin reactivity in peripheric vessels. However, chronic exercise training does not seem to be able to limit the increased vasoconstriction to ET-1 stimulation induced by chronic hypoxia exposure.

Effet de l’huile d’argan sur la contractilité de l’aorte : susceptibilité au stress oxydatif

The aim of the present study was to evaluate the effect of long-term argan oil administration on vascular responsiveness and susceptibility to H<sub>2<sub/>O<sub>2<sub/>. 16 Wistar rats were divided into 2 groups; control group and treated group receiving 5 ml/kg/day of argan oil. After 8 weeks of treatment, vascular contractility was measured on isolated aortic rings from both groups by addition to the organ bath of cumulative concentration of vasoactive drugs (phenylephrine, acetylcholine and sodium nitroprussiate). In parallel, these isolated aortic rings were exposed to increasing doses of H<sub>2<sub/>O<sub>2<sub/> (0, 1, 5 and 10 mM) for 20 minutes and the residual vascular response to phenylephrine (PE 10<sup>−6<sup/> M) and acetylcholine (Ach 10<sup>−6<sup/> M) was evaluated. Our results show that no significant differences between control and argan oil group were observed. Maximal contraction response to 10<sup>−6<sup/> MPE was 1.68 ± 0.20 g and 2.14 ± 0.20 g for control and argan oil groups, respectively. In precontracted isolated aortic rings, endothelium dependent relaxation to acetylcholine and endothelium-independent relaxation were not influenced by the diet. Maximal relaxation in response to 10<sup>−6<sup/>M of Ach was 54 % for control group and 47 % for argan oil group. Addition of hydrogen peroxide (H<sub>2<sub/>O<sub>2<sub/>) to the organ bath for 20 minutes led to a dosedependent alteration of vascular reactivity, which was characterized by similar decrease in both the PE-induced contraction and the Ach-induced relaxation in the two experimental groups. These results suggest that argan oil treatment does not influence vascular reactivity nor its sensitivity to the oxidative stress.