Endothelium-intact Aortic Rings Research Articles

Mechanisms Underlying Sesamolin-Induced Attenuation of Vascular Dysfunction in Rats With Streptozotocin-Induced Diabetes

: Background: Cardiovascular disorders constitute the major causes of morbidity and mortality among diabetic patients.Objectives: The effect of chronic sesamolin administration was studied on aortic reactivity of rats with streptozotocin (STZ)-induced diabetesMaterials and Methods: One week after induction of diabetes, male rats received sesamolin for 7 weeks. The contractile responses to KCl and phenylephrine (PE) and the relaxation response to acetylcholine (ACh) were measured in aortic rings.Results: The maximum contractile response to PE of endothelium-intact aortic rings was significantly lower in sesamolin-treated diabetic rats than in untreated diabetic rats. Removal of the endothelium from the aortic rings abolished this difference. The endothelium-dependent relaxation response to ACh was significantly higher in sesamolin-treated diabetic rats than in untreated diabetic rats. Pretreatment of aortic rings with the nitric oxide synthase inhibitor N(G) -nitro-L-arginine methyl ester (L-NAME) significantly attenuated the observed response. A 2-month course of diabetes also resulted in elevated malondialdehyde (MDA) and decreased superoxide dismutase (SOD) activity; sesamolin treatment reversed the increased MDA level and reversed the reduced SOD activityConclusions: We conclude that chronic treatment of diabetic rats with sesamolin can prevent abnormal changes in vascular reactivity via nitric oxide regulation and attenuation of oxidative stress in aortic tissue. Furthermore, endothelial integrity is necessary for sesamolin’s beneficial effect. Implication for health policy/practice/research/medical education:This study has potential application in development of new treatment strategies for attenuation of diabetes-induced vascular complications. Please cite this paper as:Mechanisms Underlying Sesamolin-Induced Attenuation of Vascular Dysfunction in Rats With Streptozotocin-Induced Diabetes. Int J Endocriol Metab.2011;9(2):311-6. DOI: 10.5812/kowsar.1726913X.2380 Copyright © 2011, Kowsar M.P.Co. All rights reserved.

Vasorelaxant effects of aqueous leaf extract of <i>Tridax procumbens</i> on aortic smooth muscle isolated from the rat

Tridax procumbens is commonly used in traditional medicine in southern part of Nigeria for the treatment of hypertension. However, the mechanism of its antihypertensive properties remains unclear. Attempts were made to investigate the properties of direct actions of aqueous extract of the leaves of T. procumbens on mechanical responses of smooth muscles in aortic ring preparations isolated from the rat. Endothelium-intact aortic rings, isolated from the normotensive rats, had been pre-contracted with noradrenaline, and cumulative addition of the aqueous extract (0.15-1.05 mg/mL) to the bathing fluid induced a concentration-dependent relaxation. Aqueous extract of T. procumbens also attenuated the contractile responses to KCl and shifted the concentration-response curve to the right. The contractile responses to serotonin were also attenuated and the concentration-response curve was shifted to the right in the presence of the extract. The results of this study indicated that aqueous leaf extract of T. procumbens possesses vasodilatory effects on the aortic smooth muscles isolated from the rat. Based on these results, a possible mechanism involved in the relaxing actions of the extract on vascular smooth muscle was discussed. The results of this study may provide a scientific basis for the use of this extract to the treatment of hypertension in Nigerian traditional medicine.

Vascular Hyporeactivity to Angiotensin II and Noradrenaline in a Rabbit Model of Obesity

This study was conducted to explore the vascular reactivity of angiotensin II and noradrenaline and their relationship with endothelial function in rabbits fed a high-fat diet (HFD). The animals were fed either an HFD or regular chow [control diet (CD)]. After 12 weeks, the rabbits fed the HFD showed higher blood pressure, body weight, and insulin levels. Glucose tolerance was impaired and positively related to blood pressure. An endothelium-independent decrease of the sensitivity to angiotensin II [pD2 endothelium-intact aortic rings (E+) in CD: 8.02 ± 0.07 vs. HFD: 7.60 ± 0.01; pD2 endothelium-removed aortic rings (E-) in CD: 8.16 ± 0.11 vs. HFD: 7.83 ± 0.16] and noradrenaline (pD2 E+ in CD: 6.36 ± 0.06 vs. HFD: 5.29 ± 0.06; pD2 E- in CD: 6.11 ± 0.08 vs. HFD: 5.80 ± 0.08) was found. Noradrenaline desensitized the angiotensin II response (pD2 with noradrenaline pretreatment in E+: 7.03 ± 0.16; in E-: 7.10 ± 0.02), but angiotensin II did not change the noradrenaline response. Acetylcholine maximal relaxation and basal nitric oxide (NO) release were comparable in both diet groups. The efficacy of angiotensin II (Rmax CD: 4604 ± 574 mg vs. HFD: 3251 ± 533 mg) and noradrenaline (Rmax CD: 11,675 ± 804 mg vs. HFD: 7975 ± 960 mg) was reduced in E+. L-N-nitroarginine methyl ester (L-NAME) recovered the efficacy of noradrenaline (Rmax L-NAME: 12,015 ± 317 mg). In contrast, L-NAME had no effect on the angiotensin II response. Noradrenaline enhanced NO levels, but angiotensin II did not. Therefore, NO was associated with hyporeactivity to noradrenaline. The resting potential was more negative in E+, and the endothelium diminished the angiotensin II-induced depolarization. These findings demonstrated that the crosstalk and the endothelium may induce hyporeactivity to angiotensin II and noradrenaline as a mechanism to compensate the increase in the blood pressure in HFD-induced obesity.

In-vitro characterization of the pharmacological effects induced by (–)-α-bisabolol in rat smooth muscle preparations

The present study deals with the pharmacological effects of the sesquiterpene alcohol (-)-α-bisabolol on various smooth-muscle preparations from rats. Under resting tonus, (-)-α-bisabolol (30-300µmol/L) relaxed duodenal strips, whereas it showed biphasic effects in other preparations, contracting endothelium-intact aortic rings and urinary bladder strips, and relaxing these tissues at higher concentrations (600-1000µmol/L). In preparations precontracted either electromechanically (by 60mmol/L K(+)) or pharmacomechanically (by phenylephrine or carbachol), (-)-α-bisabolol showed only relaxing properties. The pharmacological potency of (-)-α-bisabolol was variable, being higher in mesenteric vessels, whereas it exerted relaxing activity with a lesser potency on tracheal or colonic tissues. In tissues possessing spontaneous activity, (-)-α-bisabolol completely decreased spontaneous contractions in duodenum, whereas it increased their amplitude in urinary bladder tissue. Administered in vivo, (-)-α-bisabolol attenuated the increased responses of carbachol in tracheal rings of ovalbumin-sensitized rats challenged with ovalbumin, but was without effect in the decreased responsiveness of urinary bladder strips in mice treated with ifosfamide. In summary, (-)-α-bisabolol is biologically active in smooth muscle. In some tissues, (-)-α-bisabolol preferentially relaxed contractions induced electromechanically, especially in tracheal smooth muscle. The findings from tracheal rings reveal that (-)-α-bisabolol may be an inhibitor of voltage-dependent Ca(2+) channels.

Vasodilatory activity and antihypertensive profile mediated by inhibition of phosphodiesterase type 1 induced by a novel sulfonamide compound

LASSBio-985 is a sulfonamide compound designed as a simplified structure of a nonselective phosphodiesterase type 4 (PDE-4) inhibitor that promotes vasodilatory activity in vitro. PDE are enzymes responsible for the hydrolysis of cyclic adenosine 3',5'- monophosphate and cyclic guanosine 3',5'-monophosphate. Five different isozymes of PDE are found in vascular smooth muscle (PDE1-PDE5). Aortic rings, with or without endothelium, from male normotensive and spontaneously hypertensive rats (SHR) were prepared for isometric tension recording. Blood pressure was measured in Wistar Kyoto (WKY) rats and SHR during intravenous infusion of LASSBio-985 (10 mg/kg/min) during 15 min. LASSBio-985 induced a concentration-dependent vasodilation in aortic rings from normotensive and SHR, which was almost completely inhibited in endothelium-denuded vessels. Vasodilatory activity was also reduced in endothelium-intact aortic rings that had been pretreated with N(ω)-nitro-L-arginine methyl ester hydrochloride (L-NAME), a nitric oxide synthase inhibitor and 1H-[1,2,4]oxadiazolod[4,3-a]quinoxalin-1-one (ODQ), a guanylate cyclase inhibitor. LASSBio-985-induced vasodilation was also inhibited by sildenafil (100 μm) and SQ 22536, a PDE5 inhibitor and adenylate cyclase inhibitor, respectively. To evaluate the involvement of some endothelial receptors, atropine, diphenhydramine, HOE 140, naloxone, propranolol, indomethacin, and wortmannin were tested, but none inhibited the effects of LASSBio-985. The residual effect observed on endothelium-denuded aortic rings was abolished by nicardipine, a voltage-sensitive-Ca(2+)-channel blocker. Intravenous infusion of LASSBio-985 (10 mg/kg/min) significantly reduced systolic and diastolic pressures in both WKY and SHR. LASSBio-985 is a compound with vasodilatory activity, which could be consequent to PDE1 inhibition and voltage-sensitive-Ca(2+)-channel blockade.

Validated liquid chromatographic method and analysis of content of tilianin on several extracts obtained from Agastache mexicana and its correlation with vasorelaxant effect

Ethnopharmacological relevanceTo optimize the obtention of tilianin, an antihypertensive flavonoid isolated from Agastache mexicana (Lamiaceae), a medicinal plant used in Mexico for the treatment of hypertension. Also, a validated HPLC method to quantify tilianin from different extracts, obtained by several extraction methods, was developed. Materials and methodsThe aerial parts of Agastache mexicana were dried at different temperatures (22, 40, 50, 90, 100 and 180°C) and the dry material was extracted with methanol by maceration to compare the content of the active constituent tilianin in the samples. Furthermore, EtOH:H2O (7:3), infusion and decoction extracts were prepared from air-dried samples at room temperature to compare the content and composition of the different extraction methods. Moreover, an ex vivo vasorelaxant test on endothelium-intact aortic rat rings was conducted, in order to correlate the presence of tilianin with the activity of each extract. ResultsHigher concentration and amounts of tilianin were determined from chromatograms in the obtained methanolic extracts from plant material dried at 90, 50, 40 and 22°C, followed by 100°C; however, lower concentrations were observed in dried at 180°C and EtOH:H2O (7:3). It is worth to notice that methanolic extracts with higher amount of tilianin were the most potent vasorelaxant extracts, even though these extracts were less potent than carbachol, a positive control used. Finally, decoction, infusion and EtOH:H2O (7:3) extracts did not show any vasorelaxant effect. ConclusionResults suggest that extracts with higher concentration of tilianin possess the best vasorelaxant activity, which allowed us to have a HPLC method for future quality control for this medicinal plant.

Betulinic acid ameliorates endothelium-dependent relaxation in L-NAME-induced hypertensive rats by reducing oxidative stress

ObjectiveModern pharmacological studies reveal that betulinic acid (BA), the key active constituent of traditional Chinese cardiovascular herbs Zizyphi Spinosi semen, up-regulated endothelial nitric oxide synthase (NOS) and down-regulated NADPH oxidase,...

Betulinic acid ameliorates endothelium-dependent relaxation in l-NAME-induced hypertensive rats by reducing oxidative stress

Zizyphi Spinosi semen (ZSS) is one of the most widely used traditional Chinese herbs with protective effects on the cardiovascular system. It is not clear whether betulinic acid (BA), the key active constituent of ZSS, has beneficial cardiovascular effects on N ω-nitro- l-arginine methyl ester hydrochloride ( l-NAME)-induced hypertensive rats. The objective of this study was to investigate the effect of BA on endothelium-dependent vasorelaxation in isolated aortic rings from l-NAME-induced hypertensive rats and its underlying mechanisms. Male Sprague–Dawley rats were injected with l-NAME (15 mg/kg/d, i.p.) for 4 weeks to induce hypertension. After treatment with l-NAME for 2 weeks, rats with mean blood pressure >120 mm Hg measured by tail-cuff method were considered hypertensive and then injected with BA (0.8, 4, 20 mg/kg/d, i.p.) for the last 2 weeks. The effect of BA on the tension of rat thoracic aortic rings was measured in an organ bath system. The levels of nitric oxide (NO), reactive oxygen species (ROS), and the activity of superoxide dismutase (SOD) and nitric oxide synthase (NOS) in aortas were assayed. We found that BA (0.1–100 μM) evoked a concentration-dependent vasorelaxation in endothelium-intact normal rat aortic rings, which was significantly attenuated by pretreatment with l-NAME (100 μM) or methylene blue (MB, 10 μM), but not by indomethacin (10 μM). Pretreatment with EC 50 (1.67 μM) concentration of BA enhanced the acetylcholine (ACh)-induced vasorelaxation, which was also markedly reversed by both l-NAME and MB. The blood pressure in hypertensive rats increased to 135.22 ± 5.38 mm Hg ( P < 0.01 vs. control group), which was markedly attenuated by high dose of BA. The ACh-induced vasorelaxation in hypertensive rat aortic rings was impaired, which was markedly improved by chronic treatment with BA (20 mg/kg/d) for 2 weeks. The increase of ROS level and the decrease of NO level, SOD and eNOS activities in hypertensive rat aortas were all markedly inhibited by BA. These results indicate that BA decreased blood pressure and improved ACh-induced endothelium-dependent vasorelaxation in l-NAME-induced hypertension rats, which may be mediated by reducing oxidative stress and retaining the bioavailability of NO in the cardiovascular system.

The mechanism of vasorelaxation induced by ethanol extract of Sophora flavescens in rat aorta

Sophora flavescens (SF) is a known medicinal herb for the treatment of cardiovascular symptoms associated with arrhythmia in China. However, the pharmacological action mechanisms involved have not been well studied. The aim of the present study was to define effects of roots of SF on the vascular tension and responsible mechanisms in rat thoracic aorta. Ethanol extract of the roots of SF (ESF) was examined for their vascular relaxant effect in isolated phenylephrine-precontracted rat thoracic aorta. ESF (0.1-100 μg/ml) induced relaxation of the phenylephrine-precontracted aortic rings in a concentration-dependent manner. Endothelium-denudation abolished the ESF-induced vasorelaxation. Pretreatment of the endothelium-intact aortic rings with l-NAME, an inhibitor of nitric oxide synthase, and ODQ, an inhibitor of soluble guanylyl cyclase (sGC), inhibited ESF-induced vasorelaxation. ESF increased cGMP levels of the aortic rings in a concentration-dependent manner and the effect was blocked by l-NAME and ODQ. Inhibition of K(+) channels with glibenclamide and tetraethylammonium, cyclooxygenase inhibition with indomethacin, and β-adrenergic and muscarinic receptors blockade had no effect on the ESF-induced vasorelaxation. These findings suggest that ESF relaxes vascular smooth muscle via endothelium-dependent NO-sGC-cGMP signaling pathway.

Vasorelaxant and hypotensive effects of the extract and the isolated flavonoid rutin obtained from Polygala paniculata L.

This study aimed to investigate the in-vitro and in-vivo cardiovascular effects of the crude hydroalcoholic extract from Polygala paniculata (HEPP) in rats. The procedures were performed on aortic rings and on normotensive anaesthetized rats. When tested in endothelium-intact aorta rings, HEPP (30-1000 µg/ml) produced a significant non-concentration-dependent relaxing effect (∼40%), which was completely prevented by incubation with L-NAME (nitric oxide synthase inhibitor), ODQ (soluble guanylate cyclase inhibitor) and partially inhibited by tetraethylammonium (TEA; a non-selective potassium channel blocker) and charybdotoxin (a large- and intermediate-conductance calcium-activated potassium channel blocker). In contrast, atropine (a muscarinic receptor antagonist) or pyrilamine(a histamine H1 receptor antagonist) had no effect. Furthermore, oral administration of HEPP (30-300 mg/kg) in anaesthetized rats caused a dose-dependent and sustained hypotensive action. This effect was unchanged by atropine or TEA, but was strongly reduced in rats continuously infused with L-NAME or methylene blue. Moreover, rutin (1-3 mg/kg) administered by an intravenous route also caused a dose-dependent hypotensive effect in rats. Our results demonstrated that the extract obtained from P. paniculata induces potent hypotensive and vasorelaxant effects that are dependent on the nitric oxide/guanylate cyclase pathway. These effects could be related, at least in part, to the rutin contents in this extract.

Vascular relaxation induced by aqueous extract of Lespedeza cuneata via the NO-cGMP pathway

The aqueous extract of Lespedeza cuneata G. Don. (ALC) induced vasorelaxation of phenylephrine precontracted aorta in a dose-dependent manner. This effect disappeared in the absence of functional endothelium. Pretreatment of the aortic tissues with N(G)-nitro-L-arginine methyl ester (L-NAME), or 1H-[1,2,4]-oxadiazole-[4,3-α]-quinoxalin-1-one (ODQ) blocked ALC-induced vascular relaxation. Incubation of endothelium-intact thoracic aortic rings with ALC increased cGMP production. ALC-induced cGMP production was blocked by pretreatment with L-NAME or ODQ. ALC-induced vascular relaxation was also markedly attenuated by addition of verapamil or diltiazem, but was not blocked by pretreatment with indomethacine, glibenclamide, tetraethylammonium, atropine, or propranolol. The results suggest that ALC dilates vascular smooth muscle via endothelium-dependent NO-cGMP signaling.

Vascular mechanisms of cyanidin-3-glucoside response in streptozotocin-diabetic rats

Background and objective: Considering the high incidence of cardiovascular disorders in diabetes mellitus and some evidence on the antioxidant and antidiabetic potential of cyanidin-3-glucoside (C3G), this study was conducted to evaluate the possible beneficial effect of C3G administration on vascular reactivity of isolated thoracic aorta in diabetic rats and some of its underlying mechanisms. Materials and methods: Male diabetic rats received C3G (10 mg/kg; i.p.) on alternate days for 8 weeks one week after streptozotocin (STZ) diabetes induction. Results: It was found out that treatment of diabetic rats with C3G exerted a hypoglycaemic effect and attenuated the increased malondialdehyde (MDA) content and reduced the activity of superoxide dismutase (SOD) in aortic tissue. Maximum contractile response of endothelium-intact aortic rings to phenylephrine (PE) was significantly lower in C3G-treated diabetic rats relative to untreated diabetics and endothelium removal abolished this difference. Meanwhile, endothelium-dependent relaxation to acetylcholine (ACh) was significantly higher in C3G-treated diabetic rats as compared to diabetic group. Conclusion: Chronic treatment with C3G may prevent some diabetes-related changes in vascular reactivity observed in diabetic rats directly and/or indirectly due to its hypoglycaemic effect and attenuation of lipid peroxidation and through endothelial-derived factors.

The semi-synthetic kaurane ent-16α-methoxykauran-19-oic acid induces vascular relaxation and hypotension in rats

The present work investigates the mechanisms involved in the vasorelaxant effect of ent-16α-methoxykauran-19-oic acid (KA–OCH3), a semi-synthetic derivative obtained from the kaurane-type diterpene ent-kaur-16-en-19-oic acid (kaurenoic acid). Vascular reactivity experiments were performed in aortic rings isolated from male Wistar rats using standard muscle bath procedures. The cytosolic calcium concentration ([Ca2+]c) was measured by confocal microscopy using the fluorescent probe Fluo-3 AM. Blood pressure measurements were performed in conscious rats. KA–OCH3 (10, 50 and 100μmol/l) inhibited phenylephrine-induced contraction in either endothelium-intact or endothelium-denuded rat aortic rings. KA–OCH3 also reduced CaCl2-induced contraction in a Ca2+-free solution containing KCl (30mmol/l) or phenylephrine (0.1μmol/l). KA–OCH3 (0.1–300μmol/l) concentration-dependently relaxed endothelium-intact and endothelium-denuded aortas pre-contracted with either phenylephrine or KCl, to a greater extent than kaurenoic acid. Moreover, a Ca2+ mobilisation study showed that KA–OCH3 (100μmol/l) inhibited the increase in Ca2+ concentration in smooth muscle and endothelial cells induced by phenylephrine or KCl. Pre-incubation of intact or denuded aortic rings with NG-nitro-l-arginine methyl ester (L-NAME, 100μmol/l), 7-nitroindazole (100μmol/l), wortmannin (0.5μmol/l) and 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 1μmol/l) produced a rightward displacement of the KA–OCH3 concentration–response curve. Intravenous administration of KA–OCH3 (1–10mg/kg) reduced mean arterial blood pressure in normotensive rats. Collectively, our results show that KA–OCH3 induces vascular relaxation and hypotension. The mechanisms underlying the cardiovascular actions of KA–OCH3 involve blockade of Ca2+ influx and activation of the NO-cGMP pathway.

Effects induced by inhibitors of the phosphatidylinositol 3‐kinase/Akt and nitric oxide synthase/guanylyl cyclase pathways on the isometric contraction in rat aorta: a comparative study

This work was aimed to determine whether isometric contraction in Wistar rat aorta is related to the phosphatidylinositol 3-kinase (PI3K)/Akt-dependent activation of endothelial nitric oxide synthase (eNOS). Basically, we hypothesized that additional increases in active tone occur after the pharmacological inhibition of a transduction pathway involved in NO synthesis or action. In intact aortic rings contracted with phenylephrine or high K(+), the cumulative administration of the PI3K inhibitor, LY294002, elicited significant decreases--but not supplementary increases--in tone. In endothelium-intact tissues, on the other hand, the Akt1/2 kinase inhibitor did not alter phenylephrine- and K(+)-induced isometric contractions. The PI3K inhibitor wortmannin (1 × 10(-7) m) produced a significant supplementary contraction only in endothelium-intact aortic rings precontracted with phenylephrine. Higher concentrations of this inhibitor produced relaxations of phenylephrine and high K(+)-constricted endothelium-intact and endothelium-denuded aortic rings. LY294002 and wortmannin did not cause any potentiating effect on phenylephrine- and angiotensin II-induced concentration-dependent contractile responses in endothelium-intact tissues. In intact aortic rings contracted with phenylephrine or high K(+), the addition of the NOS inhibitor, L-NAME, or the guanylyl cyclase inhibitor, ODQ, further augmented tone in a concentration-dependent manner, and these supplementary contractions were significantly reduced by endothelium removal. Taken together, our data suggest that the PI3K/Akt pathway is not counteracting aortic isometric contractions by activation of the eNOS. It appears, on the other hand, that the smooth muscle PI3K can stimulate contraction without activation of the protein kinase Akt in response to GPCR agonists and high K(+).

Vasomodulatory effect of novel peroxovanadate compounds on rat aorta: Role of rho kinase and nitric oxide/cGMP pathway

The present study was undertaken to assess the role of reactive oxygen species (ROS) in rat aortic ring vasoreactivity and integrity by using various peroxovanadate (pV) compounds. All the pV compounds (1nM–300μM) used in the present study exerted concentration-dependent contractions on endothelium intact rat aortic rings. All compounds with an exception of DPV-asparagine (DPV-asn) significantly altered vascular integrity as shown by diminished KCl responses. Phenylephrine (PE)-mediated contractions (3nM–300μM) were unaltered in the presence of these compounds. Acetylcholine (Ach)-mediated relaxation in PE (1μM) pre-contracted rings was significantly reduced in presence of diperoxovanadate (DPV), poly (sodium styrene sulfonate-co-maleate)-pV (PSS-CoM-pV) and poly (sodium styrene 4-sulfonate)-pV (PSS-pV). However, no significant change in Ach-mediated responses was observed in the presence of poly (acrylate)-pV (PAA-pV) and DPV-asn. DPV-asn was thus chosen to further elucidate mechanism involved in peroxide mediated modulation of vasoreactivity. DPV-asn (30nM–300μM) exerted significantly more stable contractions, that was found to be catalase (100U/ml) resistant in comparison with H2O2 (30nM–300μM) in endothelium intact aortic rings. These contractile responses were found to be dependent on extracellular Ca2+ and were significantly inhibited in presence of ROS scavenger N-acetylcysteine (100μM). Intracellular calcium chelation by BAPTA-AM (10μM) had no significant effect on DPV-asn (30nM–300μM) mediated contraction. Pretreatment of aortic rings by rho-kinase inhibitor Y-27632 (10μM) significantly inhibited DPV-asn-mediated vasoconstriction indicating role of voltage-dependent Ca2+ influx and downstream activation of rho-kinase. The small initial relaxant effect obtained on addition of DPV-asn (30nM–1μM) in PE (1μM) pre-contracted endothelium intact rings, was prevented in the presence of guanylate cyclase inhibitor, methylene blue (10μM) and/or nitric oxide synthase (NOS) inhibitor, l-NAME (100μM) suggesting involvement of nitric oxide and cGMP. DPV-asn, like H2O2, exerted a response of vasoconstriction in normal arteries and vasodilation at low concentrations (30nM–1μM) in PE-pre contracted rings with overlapping mechanisms. These findings suggest usefulness of DPV-asn having low toxicity, in exploring the peroxide-mediated effects on various vascular beds. The present study also convincingly demonstrates role of H2O2 in the modulation of vasoreactivity by using stable peroxide DPV-asn and warrants future studies on peroxide mediated signaling from a newer perspective.

Activation of MEK1/ERK1/2/iNOS/sGC/PKG pathway associated with peroxynitrite formation contributes to hypotension and vascular hyporeactivity in endotoxemic rats

Increased production of inducible nitric oxide (NO) synthase (iNOS)-derived NO contributes to fall in blood pressure and vascular reactivity during endotoxemia. We investigated whether an increase in protein expression and activity of the enzymes involved in mitogen-activated protein kinase kinase 1 (MEK1)/extracellular signal-regulated kinase 1/2 (ERK1/2)/iNOS/soluble guanylyl cyclase (sGC)/protein kinase G (PKG) pathway associated with peroxynitrite production would contribute to endotoxin-induced decrease in mean blood pressure (MAP) and vascular reactivity in rats. A selective iNOS inhibitor, 1,3-PBIT (10 mg/kg, i.p.), or a selective inhibitor ERK1/2 phosphorylation by MEK1, U0126 (5 mg/kg, i.p.), prevented endotoxin (10 mg/kg, i.p.)-induced decrease in MAP and vascular reactivity to norepinephrine (0.001–100 μM) in endothelium-intact and -denuded arteries associated with increased levels of nitrite (an index for NO production), cyclic GMP (an index for sGC activity), phosphorylated vasodilator stimulated phosphoprotein (an index for PKG activity), and nitrotyrosine (an index for peroxynitrite production). Endotoxin-induced increase in the phosphorylated MEK1 protein levels were not changed by 1,3-PBIT or U0126. U0126 prevented the endotoxin-induced increase in phosphorylated ERK1/2 and iNOS expressions. A selective sGC inhibitor, ODQ (3 μM), prevented the endotoxin-induced decrease in the E max values and increase in the EC 50 values of norepinephrine in endothelium-intact aortic rings isolated from endotoxemic rats in vitro. ODQ also reversed the effect of endotoxin on the increase in the EC 50 values of norepinephrine in endothelium-denuded rings. A selective PKG inhibitor, KT5823 (1 μM), only prevented the endotoxin-induced decrease in the E max values of norepinephrine in arteries with endothelium. These results suggest that activation of MEK1/ERK1/2 pathway leading to an increase in iNOS protein expression and NO production associated with an increase in sGC and PKG activity and peroxynitrite formation results in hypotension and vascular hyporeactivity in endotoxemic rats. However, further study is needed to confirm the involvement of PKG to the fall in vascular reactivity in the rat model of endotoxemia.

Inhibitory Effect of Fentanyl on Phenylephrine-Induced Contraction on Rabbit Aorta

This in vitro study was designed to assess the effects of fentanyl on isolated rabbit thoracic aorta rings contracted with phenylephrine. Methods included contraction of aorta rings with phenylephrine (10–5 M) and recording the changes after increasing concentrations of fentanyl (10–9 M – 10–5 M). Similar experiments were done after incubation with Nω- nitro-L-arginine methyl ester (10–4 M), indomethacin (10-5 M), naloxone (10–5 M), ouabain (10–5 M), TEA (10–4 M) and glibenclamide (10–5 M). It was revealed that, fentanyl causes relaxation in rabbit aorta rings precontracted with phenylephrine. Removal of endothelium significantly reduces the relaxant response to fentanyl. Nitric oxide synthase inhibitor L-NAME, K+ channel blocker glibenclamide and Na+/K+ ATPase inhibitor ouabain inhibits the relaxant effect of fentanyl in endothelium intact aorta rings. These results suggest that fentanyl causes dose dependent vasodilatation in the rabbit aorta via activation of KATP channels and Na+-K+ -ATPase, and nitric oxide released from endothelium.

Endothelial Nitric Oxide-Dependent Vasorelaxant Effect of Isotirumalin, a Dihydroflavonol from Derris urucu, on the Rat Aorta

The present work aimed to investigate the vasorelaxant effect of isotirumalin, a dihydroflavonol isolated from Derris urucu (Leguminosae). The vasorelaxant effect of isotirumalin was investigated in the rat aorta, in the presence and in the absence of a functional endothelium. The production of nitric oxide (NO) induced by isotirumalin was measured simultaneously with its vasorelaxation using carbon microsensors. In endothelium-intact aortic rings, isotirumalin induced a concentration-dependent vasodilator effect the concentration required to produce 30% of relaxation (pIC₃₀=4.84±0.24) that was abolished in endothelium-denuded aortic rings or in the presence of Nω-nitro-L-arginine-methyl-ester (L-NAME; 300 µM). In addition, isotirumalin (100 µM) induced a simultaneous and significant increase on NO production, which was blunted in the presence of L-NAME. The present results demonstrate that isotirumalin is a vasodilator in the rat aorta and act by a mechanism dependent on the presence of a functional endothelium and on NO production.

Lack of heterologous receptor desensitization induced by angiotensin II type 1 receptor activation in isolated normal rat thoracic aorta

We tested whether heterologous receptor desensitization induced by activation of AT1 receptors may explain the purported relaxation produced by angiotensin II in normal rat aorta. Also, the role for AT2 receptors in the promotion of vasodilation was studied. In endothelium-intact and endothelium-denuded aortic rings, angiotensin II elicited biphasic contractions, which were significantly depressed when repeated in each tissue. Angiotensin II produced biphasic responses on phenylephrine preconstricted endothelium-intact and endothelium-denuded tissues, without reducing precontractile tone. These responses were abolished in the presence of the AT1 receptor antagonist losartan, but no relaxing responses to angiotensin II were uncovered. PD123319 did not influence angiotensin II responses in endothelium-intact tissues precontracted with phenylephrine; thus, under AT2 receptors blockade the contractile effects of angiotensin II were not overexposed. In conclusion, angiotensin II-induced biphasic responses can be attributed to AT1 receptors activation and rapid desensitization with time. Desensitization proved to be homologous in nature, since precontractile tone induced by phenylephrine was not depressed by angiotensin II (i.e., angiotensin II did not induce heterologous α1-adrenergic receptors desensitization). We found no functional evidence of the participation of AT2 receptors in angiotensin II elicited biphasic contractions. Angiotensin II does not exert relaxant effects in normal rat aorta.

Partial endothelium-dependent vasorelaxation of crocetin and its mechanism

To investigate the vasorelaxation effect of crocetin (CCT) and its mechanism. Isolated aortic rings from Sprague-Dawley rats were mounted in the organ bath system. The tension of the aorta was recorded. CCT significantly provoked concentration-dependent relaxation in both endothelium-intact and-denuded aortic rings pre-constricted by phenylephrine (10⁻⁵ mol/L), and the vasorelaxation in endothelium-intact aortic rings was stronger than that in endothelium-denuded ones. CCT had no significant effects on aortic rings pre-constricted with KCl (6 × 10⁻² mol/L). Pretreatment with eith L-NAME (10⁻⁴ mol/L), an inhibitor of nitric oxide synthase (NOS), or indomethacin (10⁻⁵ mol/L), an inhibitor of cyclooxygenase, for 30 min significantly attenuated the relaxation of endothelium-intact aortic rings induced by CCT. Besides, both tetraethylammonium (a Ca²(+)-activated K(+) channel inhibitor, 5 × 10⁻³ mol/L) and 4-aminopyridine (a voltage-sensitive K(+) channel inhibitor, 10⁻³ mol/L), but not the ATP-sensitive K(+) channel inhibitor glibenclamide (3 × 10⁻⁶ mol/L), significantly attenuated CCT-induced relaxation in endothelium-denuded aortic rings. CCT had partial endothelium-dependent relaxation in rat aortas, which may be mediated by activating the endothelial NOS-NO and cyclooxygenase-prostacyclin pathways. The endothelium-independent relaxation in rat aortas induced by CCT may be mediated by Ca²(+)-activated K(+) channels and voltage-sensitive K(+) channels.