Endothelium-intact Aortic Rings Research Articles

The Protective Effect of Indole Alkaloid Vincanine Against Hypoxia-Induced Vasorelaxation Model of Rat Aorta

Introduction: Using conventional organ bath procedures, the current study sought to determine how vincanine hydrochloride affected vasorelaxation brought on by hypoxia in rat aortic rings. Methods: To induce hypoxia, we used a glucose-free Krebs solution that was infused with 95% N2 and 5% CO2. After 60 minutes of hypoxia, the effect of vincanine was evaluated on aortic rings that were precontracted with either 50 mM KCl or 1 µM phenylephrine (PE). The effect of vincanine was more noticeable in aortic rings that had been precontracted by PE as opposed to KCl. Additionally, when verapamil, a blocker of L-type VDCCs, was preincubated with endothelium-intact aortic rings and KCI was used for precontraction, the effect of vincanine on hypoxia-induced vasorelaxation was significantly reduced. Results: Vincanine inhibited hypoxia-induced vasorelaxation in aortic rings precontracted with PE in a calcium-free buffer. Furthermore, the presence of glibenclamide, a specific inhibitor of ATP-sensitive K+-channels (KATP), and tetraethylammonium chloride (TEA), a nonspecific inhibitor of calcium-activated large conductance K+-channels (BKca), significantly reduced the effect of vincanine on hypoxia-induced vasorelaxation. The removal of the endothelium also had a significant impact on the effect of vincanine on hypoxia-induced vasorelaxation. Conclusion: The present findings showed that alkaloid vincanine isolated from the leaves of Vinca minor H. significantly abolished the hypoxia-induced vasorelaxation in rat aorta. The obtained results suggest that vincanine may protect the rat aorta against hypoxic injuries in the vasculature.

[Effect of asiaticoside on systolic blood pressure and relaxation of isolated thoracic aorta of rats].

To investigate the effect of asiaticoside on blood pressure and relaxation of thoracic aorta in rats and explore the underlying mechanism. SD rats treated with 50 and 100 mg/kg asiaticoside by daily gavage for 2 weeks were monitored for systolic blood pressure changes, and histological changes of the thoracic aorta were evaluated using HE staining. In isolated rat endothelium-intact and endothelium-denuded thoracic aorta rings, the effects of asiaticoside on relaxation of the aortic rings were tested at baseline and following norepinephrine (NE)- and KCl-induced constriction. The vascular relaxation effect of asiaticoside was further observed in NE-stimulated endothelium-intact rat aortic rings pretreated with L-nitroarginine methyl ester, indomethacin, zinc protoporphyrin Ⅸ, tetraethyl ammonium chloride, glibenclamide, barium chloride, Iberiotoxin, 4-aminopyridine, or TASK-1-IN-1. The aortic rings were treated with KCl and NE followed by increasing concentrations of CaCl2 to investigate the effect of asiaticoside on vasoconstriction induced by external calcium influx and internal calcium release. Asiaticoside at 50 and 100 mg/kg significantly lowered systolic blood pressure in rats without affecting the thoracic aorta histomorphology. While not obviously affecting resting aortic rings with intact endothelium, asiaticoside at 100 mg/kg induced significant relaxation of the rings constricted by KCl and NE, but its effects differed between endothelium-intact and endothelium-denuded rings. In endothelium-intact aortic rings pretreated with indomethacin, ZnPP Ⅸ, barium chloride, glyburide, TASK-1-IN-1 and 4-aminopyridine, asiaticoside did not produce significant effect on NE-induced vasoconstriction, and tetraethylammonium, Iberiotoxin and L-nitroarginine methyl ester all inhibited the relaxation effect of asiaticoside. In KCland NE-treated rings, asiaticoside obviously inhibited CaCl2-induced vascular contraction. Asiaticoside induces thoracic aorta relaxation by mediating high-conductance calcium-activated potassium channel opening, promoting nitric oxide release from endothelial cells and regulating Ca2+ influx and outflow, thereby reducing systolic blood pressure in rats.

Endothelium-dependent vasorelaxation effects of F5 fraction of Crinum amabile chloroform extract

BackgroundVascular dysfunction can lead to many health problems including hypertension and heart disease. The complexities of vascular dysfunction and vascular disorder-related diseases have prompted the search for many new biologically active compounds in the efforts of resolving the problems. Previous studies have shown that Amaryllidaceae alkaloids exert multiple biological activities, including the vasorelaxation effect. Crinum amabile, which is a family member of Amaryllidaceae, is believed to possess a promising pharmacological activity as a vasorelaxant.MethodThe vasorelaxation activities of Crinum amabile extracts and fractions were determined using in vitro models of phenylephrine pre-contracted intact and denuded rat aortic rings. The mechanistic pathways of vasorelaxation were investigated by pre-treatment of endothelium-intact rat aortic rings with L-NG Nitro Arginine Methyl Ester (L-NAME), methylene blue (MB), indomethacin, atropine and propranolol, respectively.ResultsThe results showed that chloroform extract (CE) of Crinum amabile exhibited the highest vasorelaxation activity, and further fractionation of CE found that its F5 fraction exerted the strongest activity. An in-depth study on the mechanistic pathway revealed that the endothelium-dependent vasorelaxation induced by F5 fraction was primarily achieved through stimulation of prostaglandin (PGI2) production and partially associated with NO/cGMP activation pathway.ConclusionFindings from this study suggest that Crinum amabile can serve as a promising candidate for the discovery and development of the new vasorelaxant drug.

Mechanistic study of endothelium independent vasodilation effects of wogonin

Scutellaria baicalensis Georgi, locally known as HuangQin, and commonly as Baikal or Chinese skullcap, is an important herb in Chinese traditional medicine. The flavonoids from this plant are main active substances responsible for its medicinal applications. Wogonin is one such active ingredient derived from this plant. Here, we investigated the mechanism of the vasodilation effect of wogonin on isolated rat thoracic aortas. For this study, endothelium intact and endothelium removed thoracic aortic rings were prepared from rats. Using a tension transducer, the tension of the rat thoracic aortic rings was recorded. Results showed that wogonin is able to relax the endothelium-intact aortic rings, but L-NAME, indomethacin (Indo), and methylene blue (MB) could not reduce the tension in these rings. Wogonin was also able to relax endotheliumremoved rings. However, treatment with tetraethylammonium (TEA), BaCl2, glibenclamide (Gly), 4-aminopyridine (4-AP), and verapamil (Ver) had no effect on vasodilation induced by wogonin. Using wogonin to pre-treat endothelium-removed aortic rings reduced the contraction induced by K+. Pre-treatment of endothelium-removed aortic rings with wogonin markedly reduced the contraction induced by 10-6 M PE in Ca2+-free solution. It could be concluded that L-type calcium channels and intracellular Ca2+ release is inhibited by wogonin.

Release of 6-nitrodopamine modulates vascular reactivity of Pantherophis guttatus aortic rings

6-Nitrodopamine (6-ND) is a novel catecholamine that is released from human umbilical cord vessels and Chelonoidis carbonaria aortic rings. The synthesis/release of 6-ND is inhibited by either pre-incubation of the vessels with the nitric oxide (NO) synthase inhibitor L-NAME or by mechanical removal of the endothelium. 6-ND causes powerful vasorelaxation, acting as a potent and selective dopamine D2-like receptor antagonist.Basal release of 6-ND from Panterophis guttatus endothelium intact and denuded aortic rings was quantified by LC-MS/MS. In order to evaluate the interaction of 6-ND with other catecholamines, aortic rings were suspended vertically between two metal hooks in 10-mL organ baths containing Krebs-Henseleit's solution and attached to isometric transducers.Endothelium intact aortic rings presented basal release of 6-ND, which was significantly reduced by previous incubation with L-NAME (100 μM). In endothelin-1 (3 nM) pre-contracted endothelium intact aortic rings, 6-ND (10pM-1 μM) and the dopamine D2-receptor antagonist L-761,626 (10 pM–1 μM) induced concentration-dependent relaxations, which were not affected by incubation with L-NAME but greatly reduced in endothelium-removed aortic rings.6-ND (0.1–1 μM) produced significant rightward shifts of the concentration-response curves to dopamine in L-NAME pre-treated endothelium-intact (pA2 7.01) rings. Contractions induced by noradrenaline and adrenaline were not affected by pre-incubation with 6-ND (1 μM). The EFS-induced contractions of L-NAME pre-treated endothelium-intact aortic rings were significantly inhibited by incubation with 6-ND (1 μM).The results indicate that 6-ND released from Pantherophis guttatus aortic rings is coupled to NO release and represents a new mechanism by which NO can modulate vascular reactivity independently of cGMP production.

VASORELAXANT MECHANISM(S) OF CLERODENDRUM VOLUBILE ETHANOL LEAF EXTRACT IN NORMAL AND DOXORUBICIN-TREATED ENDOTHELIUM INTACT AORTIC RINGS

Objectives: Doxorubicin (DOX) is a highly effective antibiotics anthracycline cytotoxic agent with a broad spectrum of activity in the treatment of solid and hematological malignancies. However, DOX is notorious for inducing cardiotoxicity and vascular dysfunction as its common off-target side effects. This study evaluated the possible vasorelaxant activity and mechanism(s) of action of Clerodendrum volubile ethanol leaf extract (CVE) in normal and DOX-pretreated endothelium intact aortic rings in Physiological Salt Solution (PSS) in vitro. Methods: The responses were recorded isometrically by an organ bath connected to Data Capsule Acquisition System. Effects of CVE on phenylephrine-precontracted endothelium intact rat aortic rings and the influence of the respective blockers for adrenergic, cholinergic, calcium channel, and prostacyclin receptors were investigated to unveil the possible underlying vasorelaxant mechanism(s) of CVE. Results: Our findings showed that CVE significantly induced vasorelaxation in phenylephrine hydrochloride (PE) and KCl precontracted endothelium intact aortic rings in a concentration-dependent manner. Furthermore, the CVE-induced vasorelaxation in PE- and KCl-precontracted aortic rings were inhibited by pre-incubation with atropine and indomethacin indicating that the vasorelaxant effect of CVE was profoundly mediated through cholinergic and prostacyclin mechanisms. Conclusion: Overall, results of this study report for the first time the vasorelaxant effect of CVE in isolated endothelium-intact doxorubicin-treated aortic rings of normotensive rats which was probably cholinergic and prostacyclin-mediated. Thus, results of this study provide further insight into the cardioprotective mechanism of CVE in doxorubicin-induced cardiotoxicity beyond the antioxidant and anti-apoptosis mechanisms that have been previously reported.

6-Nitrodopamine is an endogenous selective dopamine receptor antagonist in Chelonoidis carbonaria aorta

Chelonoidis carbonaria aortic rings present endothelium-derived release of dopamine, noradrenaline, adrenaline and 6-nitrodopamine (6-ND). Here it was investigated whether 6-ND release is coupled to nitric oxide (NO) synthesis and its action on the vascular smooth muscle reactivity.Basal release of 6-ND from aortic rings in the absence and presence of the NO synthesis inhibitor L-NAME was quantified by LC-MS-MS. Aortic rings were suspended vertically between two metal hooks in 10-mL organ baths containing Krebs-Henseleit's solution and attached to isometric transducers. The tissues were allowed to equilibrate for 1 h before starting the experiments.The release of 6-ND was significantly reduced by previous incubation with L-NAME. 6-ND (up to 300 μM) had no contractile activity in the aortic rings. 6-ND (1, 3 and 10 μM) produced significant rightward shifts of the concentration-response curves to dopamine in endothelium-intact (pA2 6.09) and L-NAME pre-treated endothelium-intact (pA2 7.06) aortic rings. Contractions induced by noradrenaline and adrenaline were not affected by pre-incubation with 6-ND. The EFS (16 Hz)-induced aortic contractions were significantly inhibited by incubation with 6-ND (10 μM).In the thromboxane A2 mimetic U-46619 (30 nM) pre-contracted endothelium intact aortic rings, 6-ND (1 nM–1 μM) and the dopamine D2-receptor antagonist haloperidol (1 nM-1 μM) induced concentration-dependent relaxations. The relaxations were not present in endothelium-removed aortic rings but they were not affected by incubation with L-NAME in endothelium-intact aortic rings.The results indicate that the synthesis of this novel catecholamine in Chelonoidis carbonaria aortic rings is coupled to NO release and that 6-ND acts as a highly selective dopamine D2-like receptor antagonist.

Safranal Induces Vasorelaxation by Inhibiting Ca2+ Influx and Na+/Ca2+ Exchanger in Isolated Rat Aortic Rings.

Introduction: Safranal, which endows saffron its unique aroma, causes vasodilatation and has a hypotensive effect in animal studies, but the mechanisms of these effects are unknown. In this study, we investigated the mechanisms of safranal vasodilation. Methods: Isolated rat endothelium-intact or -denuded aortic rings were precontracted with phenylephrine and then relaxed with safranal. To further assess the involvement of nitric oxide, prostaglandins, guanylate cyclase, and phospholipase A2 in safranal-induced vasodilation, aortic rings were preincubated with L-NAME, indomethacin, methylene blue, or quinacrine, respectively, then precontracted with phenylephrine, and safranal concentration–response curves were established. To explore the effects of safranal on Ca2+ influx, phenylephrine and CaCl2 concentration–response curves were established in the presence of safranal. Furthermore, the effect of safranal on aortic rings in the presence of ouabain, a Na+-K+ ATPase inhibitor, was studied to explore the contribution of Na+/Ca2+ exchanger to this vasodilation. Results: Safranal caused vasodilation in endothelium-intact and endothelium-denuded aortic rings. The vasodilation was not eliminated by pretreatment with L-NAME, indomethacin, methylene blue, or quinacrine, indicating the lack of a role for NO/cGMP. Safranal significantly inhibited the maximum contractions induced by phenylephrine, or by CaCl2 in Ca2+-free depolarizing buffer. Safranal also relaxed contractions induced by ouabain, but pretreatment with safranal totally abolished the development of ouabain contractions. Discussion/Conclusion: Inhibition of Na+-K+ ATPase by ouabain leads to the accumulation of Na+ intracellularly, forcing the Na+/Ca2+ exchanger to work in reverse mode, thus causing a contraction. Inhibition of the development of this contraction by preincubation with safranal indicates that safranal inhibited the Na+/Ca2+ exchanger. We conclude that safranal vasodilation is mediated by the inhibition of calcium influx from extracellular space through L-type Ca2+ channels and by the inhibition of the Na+/Ca2+ exchanger.

The predominance of endothelium-derived relaxing factors and beta-adrenergic receptor pathways in strong vasorelaxation induced by 4-hydroxybenzaldehyde in the rat aorta.

4-hydroxybenzaldehyde (4HB), known as ρ-hydroxybenzaldehyde, is commonly present in traditional Chinese medicine herb, most frequently used for hypertension treatment. This research aims to determine the potency of 4HB's vasorelaxant action. In the study, the vasodilation effect of 4HB was evaluated using in vitro isolated rat aortic rings assay. The aortic rings were pre-incubated with respective antagonists before being pre-contracted with phenylephrine (PE) and challenged with various concentrations of 4HB for mechanistic action studies. Rmax (maximal vasodilation) and pEC50 (negative logarithm of half-maximal effective concentration) values of each experiment were determined for comparison purposes. 4HB caused vasodilation on endothelium-intact aortic rings which pre-contracted with PE (pEC50 = 3.53±0.05, Rmax = 100.95±4.25%) or potassium chloride (pEC50 = 2.96±0.13, Rmax = 72.13±4.93%). The vasodilation effect of 4HB was significantly decreased in the absence of an endothelium (pEC50 = 2.21±0.25, Rmax = 47.96±4.16%). The atropine, 4-aminopyridine, Nω-nitro-L-arginine methyl ester, glibenclamide, and propranolol significantly reduced the vasorelaxation effect of 4HB. Besides that, 4HB blocked the voltage-operated calcium channel (VOCC) and regulated the intracellular Ca2+ release from the sarcoplasmic reticulum (SR) in the aortic ring. Thus, the results indicated that 4HB exerted its vasodilatory effect via cGMP and β2 pathways, M3-dependent PLC/IP3 pathways, and potassium and calcium channels.

Quercetin and resveratrol ameliorate nickel-mediated hypercontraction in isolated Wistar rat aorta.

The ameliorative potential of quercetin and resveratrol on isolated endothelium-intact aortic rings incubated with nickel was examined. The effect of varying concentrations of quercetin and resveratrol was investigated on isolated Wistar rat aortic rings using an organ bath system over vasoconstrictor phenylephrine (PE) at 1 µM. To delineate the mechanism of action, isolated aortic rings were pre-incubated with pharmacological modulators, such as verapamil 1 µM, apocynin 100 µM, indomethacin 100 µM or N-G-nitro-L-arginine methyl ester (L-NAME) 100 µM, separately, before incubation with 100 µM quercetin and 30 µM resveratrol. To assess the ameliorative and prophylactic potentials of quercetin and resveratrol, aortic rings were also incubated with quercetin or resveratrol for 40 min, followed by incubation with nickel for 40 min. At 100 µM, quercetin caused 29% inhibition of contraction, while resveratrol at 30 µM caused 55% inhibition of contraction in aortic rings compared with control. Aortic rings incubated with contractile modulators, such as verapamil, apocynin, indomethacin or N-G-nitro-L-arginine methyl ester (L-NAME), along with quercetin or resveratrol at their concentrations producing maximum relaxant effect, showed that both of these natural compounds exert their relaxant effect by inhibiting the generation of reactive oxygen species (ROS) from endothelial and smooth muscle cells, blocking voltage-gated calcium channels, and increasing the release of nitric oxide (NO). The mediation of hypercontraction by nickel is due to the increased ROS and the influx of calcium through voltage-dependent calcium channels. These natural compounds are shown to counter the nickel-induced effects, appearing as effective ameliorators. In this study, we found that quercetin and resveratrol act as ameliorators of nickel-mediated hypercontraction by decreasing ROS and enhancing NO release from endothelial cells.

Irisin relaxes rat thoracic aorta: MEK1/2 signaling pathway, KV channels, SKCa channels, and BKCa channels are involved in irisin-induced vasodilation.

This study investigated the effects of irisin on vascular smooth muscle contractility in rat thoracic aorta, and the hypothesis that mitogen-activated protein kinase kinase (MEK1/2) signaling pathway, voltage-gated potassium (KV) channels, small-conductance calcium-activated potassium (SKCa) channels, and large-conductance calcium-activated potassium (BKCa) channels may have roles in these effects. Isometric contraction-relaxation responses of isolated thoracic aorta rings were measured with an organ bath model. The steady contraction was induced with 10-5M phenylephrine (PHE), and then the concentration-dependent responses of irisin (10-9-10-6 M) were examined in endothelium-intact and -denuded rat thoracic aortas. Also, the effects of irisin incubations on PHE-mediated contraction and acetylcholine (ACh) - mediated relaxation were studied. Irisin exerted the vasorelaxant effects in both endothelium-intact and -denuded aortic rings at concentrations of 10-8, 10-7, and 10-6M compared with the control groups (p< 0.001). Besides, pre-incubation of aortic rings with irisin (10nM, 100nM, or 1µM for 30min) augmented ACh-mediated (10-9-10-5) vasodilation in PHE-precontracted thoracic aorta segments but did not modulate PHE-mediated (10-9-10-5) contraction. In addition, MEK1/2 inhibitor U0126, KV channel blocker XE-991, SKCa channel blocker apamin, and BKCa channel blocker tetraethylammonium (TEA) incubations significantly inhibited the irisin-induced relaxation responses. In conclusion, the first physiological findings were obtained regarding the functional relaxing effects of irisin in rat thoracic aorta. The findings demonstrated that irisin induces relaxation responses in endothelium-intact and (or) endothelium-denuded aortic rings in a concentration-dependent manner. Furthermore, this study is the first to report that irisin-induced relaxation responses are related to the activity of the MEK1/2 pathway, KV channels, and calcium-activated K+ (SKCa and BKCa) channels.

Combined antihypertensive effect of unripe Rubus coreanus Miq. and Dendropanax morbiferus H. L\xe9v. Extracts in 1 kidney-1 clip hypertensive rats and spontaneously hypertensive rats

BackgroundWe previously showed that enzymatically hydrolyzed Dendropanax morbiferus H. Lév. leaf (Hy-DP) and unripe Rubus coreanus Miq. (5-uRCK) extracts exhibit potent vasodilator effects on isolated aortic rings from rats partly through endothelium-dependent and endothelium-independent mechanisms. These two extracts have different mechanisms of action; however, their combined effect on antihypertensive activity has not been explored.MethodsThe present study aims to investigate the effect of a chronic optimized mixture (HDR-2, composed of Hy-DP and 5-uRCK in a 2:1 mass ratio) on vascular tension and blood pressure in two different hypertensive rat models.ResultsThe results showed that HDR-2 concentration-dependently relaxed endothelium-intact and endothelium-denuded aortic rings precontracted with phenylephrine. Antihypertensive effects were assessed in vivo on a 1 kidney-1 clip (1 K-1C) rat model of hypertension and spontaneously hypertensive rats (SHRs). Acute HDR-2 treatment significantly decreased systolic blood pressure (SBP) 3 h posttreatment in both models. Chronic HDR-2 administration also significantly decreased SBP in the hypertensive rat models. Moreover, HDR-2 increased eNOS protein expression and phosphorylation levels in the aorta.ConclusionChronic HDR-2 administration may effectively improve vascular function by decreasing plasma angiotensin-converting enzyme (ACE) activity and AngII levels. HDR-2 significantly improved acetylcholine (ACh)-induced aortic endothelium-dependent relaxation and affected sodium nitroprusside (SNP)-induced endothelium-independent relaxation in SHRs.

Vasorelaxant effect of 5,7,4′- Trihydroxyflavanone (Naringenin) via endothelium dependent, potassium and calcium channels in Sprague Dawley rats: Aortic ring model

Naringenin is a naturally occurring flavanone (flavonoid) known to have bioactive effects on human health. It has been reported to show cardiovascular effects. This study aimed to investigate the possible vasorelaxant effect of naringenin and the mechanism behind it by using a Sprague Dawley rat aortic ring assay model. Naringenin caused significant vasorelaxation of endothelium-intact aortic rings precontracted with phenylephrine (pD2 = 4.27 ± 0.05; Rmax = 121.70 ± 4.04%) or potassium chloride (pD2 = 4.00 ± 0.04; Rmax = 103.40 ± 3.82%). The vasorelaxant effect decreased in the absence of an endothelium (pD2 = 3.34 ± 0.10; Rmax = 62.29 ± 2.73%). The mechanisms of the vasorelaxant effect of naringenin in the presence of antagonists were also investigated. Indomethacin, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, atropine, 4-aminopyridine, Nω-nitro-l-arginine methyl ester, glibenclamide and propranolol significantly reduced the relaxation stimulated by naringenin in the presence of endothelium. Besides that, the effect of naringenin on the voltage-operated calcium channel (VOCC) in the endothelium-intact aortic ring was studied, as was intracellular Ca2+ release from the sarcoplasmic reticulum (SR) in the endothelium-denuded aortic ring. The results showed that naringenin also significantly blocked the entry of Ca2+ via the VOCC, SERCA/SOCC and suppressed the release of Ca2+ from the SR. Thus, the vasorelaxant effect shown by naringenin mostly involve the COX pathway, the endothelium-dependent pathway via NO/sGC/prostaglandin, calcium and potassium channels.

New Therapeutic Insight into the Effect of Ma Huang Tang on Blood Pressure and Renal Dysfunction in the L-NAME-Induced Hypertension

In this study, we evaluated the effect of a traditional herbal formula, Ma Huang Tang (MHT), on blood pressure and vasodilation in a rat model of NG‐nitro‐L‐arginine methylester- (L-NAME-) induced hypertension. We found that MHT-induced vascular relaxation in a dose-dependent manner in rat aortas pretreated with phenylephrine. However, pretreatment of endothelium-intact aortic rings with L‐NAME, an inhibitor of nitric oxide synthesis (NOS), or 1H‐[1, 2, 4]‐oxadiazole‐[4, 3‐α]‐quinoxalin‐1‐one (ODQ), an inhibitor of soluble guanylyl cyclase, significantly abolished vascular relaxation induced by MHT. MHT also increased the production of guanosine 3′,5′-cyclic monophosphate (cGMP) in the aortic rings pretreated with L-NAME or ODQ. To examine the in vivo effects of MHT, Sprague Dawley rats were treated with 40 mg/kg/day L-NAME for 3 weeks, followed by administration of 50 or 100 mg/kg/day MHT for 2 weeks. MHT was found to significantly normalize systolic blood pressure and decreased intima-media thickness in aortic sections of rats treated with L-NAME compared to that of rats treated with L-NAME alone. MHT also restored the L-NAME-induced decrease in vasorelaxation response to acetylcholine and endothelial nitric oxide synthase (eNOS) and endothelin-1 (ET-1) expression. Furthermore, MHT promoted the recovery of renal function, as indicated by osmolality, blood urea nitrogen (BUN) levels, and creatinine clearance. These results suggest that MHT-induced relaxation in the thoracic aorta is associated with activation of the nitric oxide/cGMP pathway. Furthermore, it provides new therapeutic insights into the regulation of blood pressure and renal function in hypertensive patients.

Vasorelaxant effect of the dichloromethane fraction from Lippia thymoides involves voltage-gated potassium channels and the suppression of intracellular calcium in rat aortae

The crude extract and fractions from the leaves and stems of Lippia thymoides Mart. & Schauer, Verbenaceae, were evaluated to determine their vasorelaxant activity on isolated rat aortae. The chromatographic profile from the crude extract and the most potent fraction was determined by HPLC-DAD. The dichloromethane fraction (LtSD) displayed the more potent vasorelaxant effect on phenylephrine-induced tonic contractions in isolated rat aortae with (EC50 = 38.5 (26.3–56.5) μg/ml) or without (EC50 = 37.9 (28.5–50.5) μg/ml) functional endothelium. LtSD-mediated vasorelaxation in endothelium-intact aortic rings was not altered in the presence of atropine, l-NAME, indomethacin, or methylene blue. Preincubation of endothelium-denuded aortic rings with CsCl, glibenclamide, or tetraethylammonium did not alter the effects of LtSD-induced relaxation, but in the presence of 4-aminopyridine, the concentration-response curve of LtSD (EC50 = 37.63 (32.88–43.06) μg/ml in the absence of blocker) shifted to the right and the EC50 value was significantly increased to 156.0 (129.5–187.8) μg/ml. In addition, preincubation with LtSD plus nifedipine inhibited phenylephrine contractions similarly to LtSD alone. These results indicated that the vasorelaxant mechanisms of LtSD were mediated via endothelium-independent pathways, probably involving the activation of KV channels and the reduction of Ca2+ influx through intracellular stores.

Vasorelaxant effect of trans-4-chloro-β-nitrostyrene, a synthetic nitroderivative, in rat thoracic aorta.

Previously, we showed that 1-nitro-2-phenylethene, a nitrostyrene derivative of 1-nitro-2-phenylethane, induced vasorelaxant effects in rat aorta preparations. Here, we studied mechanisms underlying the vasorelaxant effects of its structural analog, trans-4-chloro-β-nitrostyrene (T4CN), in rat aortic rings. Increasing concentrations of T4CN (0.54-544.69µm) fully and similarly relaxed contractions induced by phenylephrine (PHE, 1µm) or KCl (60mm) in endothelium-intact aortic rings with IC50 values of 66.74 [59.66-89.04] and 79.41 [39.92-158.01] µm, respectively. In both electromechanical and pharmacomechanical couplings, the vasorelaxant effects of T4CN remained unaltered by endothelium removal, as evidenced by the IC50 values (108.35 [56.49-207.78] and 65.92 [39.72-109.40] µm, respectively). Pretreatment of endothelium-intact preparations with L-NAME, ODQ, glibenclamide, or TEA did not change the vasorelaxant effect of T4CN. Under Ca2+ -free conditions, T4CN significantly reduced the phasic contractions induced by caffeine or PHE, as well as the contractions due to exogenous CaCl2 in aortic preparations stimulated with PHE (in the presence of verapamil). These results suggest that in rat aortic rings, T4CN induced vasorelaxation independently from the activation of soluble guanylate cyclase/cGMP pathway, an effect that may be related to the electrophilicity of the substituted chloro-nitrostyrene. This vasorelaxation seems to involve inhibition of both calcium influx from the extracellular milieu and calcium mobilization from intracellular stores mediated by IP3 receptors and by ryanodine-sensitive Ca2+ channels.

Root essential oil of Chrysopogon zizanioides relaxes rat isolated thoracic aorta - an ex vivo approach.

Root of Chrysopogon zizanioides (L.) Roberty has been used in Siddha system of medicine to treat hypertension. The present study was therefore to investigate the vasorelaxation effect of root essential oil of C. zizanioides using rat isolated thoracic aortic rings. Chemical characterization of root essential oil was carried out using Gas Chromatography-Flame Ionization Detector (GC-FID) and Gas Chromatography-Mass Spectrometry (GC-MS). Essential oil nanoemulsion (EONE) was prepared and characterized. Vasorelaxant effect of EONE in endothelium-intact aortic rings precontracted with phenylephrine (PE) (1µM) or KCl (80mM) was investigated. Role of Ca2+, nitric oxide and K+ channels in precontracted aortic rings were investigated to elucidate the mechanism of action of the essential oil. Further, the role of muscarinic and prostacyclin receptors in EONE induced relaxation was studied. The EONE significantly induced relaxation (Emax 77.1±4.87%) in PE precontracted aortic rings. The nitric oxide synthase, and cyclooxygenase inhibitors and potassium channel blockers have not significantly inhibited the vasorelaxation induced by EONE. However, EONE induced relaxation in precontracted endothelium-intact aortic rings was significantly inhibited by muscarinic receptor and calcium channel. The root essential oil of C. zizanioides possesses vasorelaxant effect through muscarinic pathway as well as acts as calcium channel blocker.

Anti-hypertensive vasodilatory action of Gynura procumbens mediated by kaempferol 3-O-rutinoside

Introduction: Gynura procumbens (GP), otherwise known as longevity spinach or “Sambung Nyawa” in Malay, is an evergreen herb found in Africa and Southeast Asian countries (including Brunei) used traditionally to treat various diseases such as fever, diabetes and hypertension. We examined GP’s vasodilatory action to determine its possible role via the cholinergic-mediated pathway. Methods: GP leaves were prepared by filtration and evaporation to obtain the aqueous (AEGP) and methanol (MEGP) extracts followed by screening for phytochemical constituents. The total phenol, total flavonoid and flavonol contents were determined using the corresponding Folin–Ciocalteau, and aluminium colorimetric methods and the presence of kaempferol 3-O-rutinoside in the extracts was detected using HPLC analysis. Organ bath studies were conducted to determine the vasodilatory activity using intact and denuded isolated rat aortic rings by exposure to either increasing concentration of extracts (0.25, 0.5, 1.0, and 2.0 mg/mL) or 10 µg/mL kaempferol 3-O-rutinoside in the presence or absence of acetylcholine (ACh) after pre-contraction by noradrenaline (NA). Results: MEGP contained more phytochemical constituents and higher content of total flavonoid and total flavonol but less phenolic content than AEGP. Furthermore, MEGP yielded a 20% elevated amount of kaempferol 3-O-rutinoside than AEGP. Both extracts significantly amplified ACh-endothelium dependent vasodilation and mediated relaxation at 1 mg/mL in endothelium-intact and endothelium-denuded aortic rings with MEGP as a more effective vasodilator than AEGP. Overall, these results imply the involvement of extracts in potentiating cholinergic pathway, which might be mediated by kaempferol, as shown by its vasorelaxation effects in endothelium-intact and –denuded aorta. Conclusions: The present findings demonstrate that the vasodilatory activities of the two Gynura procumbens extracts, AEGP and MEGP, in thoracic aorta rings isolated from rats are potentially mediated via a cholinergic pathway through the action of a flavonoid particularly kaempferol 3-O-rutinoside.

The Involvement of ATP-Sensitive Potassium Channels in the Nebivolol-Induced Relaxation of Endothelium-Intact Aorta Isolated from Rats

Objective: Nebivolol is a highly selective beta-1 adrenergic receptor blocker with additional vasorelaxant properties. The vasorelaxant effect of nebivolol has been mainly attributed to endothelium-dependent mechanisms including beta-adrenergic receptors. However, the involvement of ATP-sensitive potassium (KATP) channels, another potential mechanism for vasorelaxant effect, in the vasorelaxant response to nebivolol remains unclear. Therefore, this study was aimed to investigate the role of KATP channels in the nebivolol-induced vasorelaxation in the isolated rat aorta Methods: The rat thoracic aortic rings isolated from Sprague-Dawley rats were mounted in organ bath chambers containing Krebs-Henseleit solution at 37 oC continuously bubbled with 95% O2 and 5% CO2. After an equilibration period, the presence of endothelium was confirmed by the response (more than 50%) to acetylcholine (10 μM) in aortic rings precontracted with phenylephrine (1 μM). After washout, in control group, the endothelium-intact aortic rings were contracted by potassium chloride (30 mM) before the cumulative addition of nebivolol (0.0001-100 μM). In some experiments, the relaxant response to nebivolol (0.0001-100 μM) was also obtained in the presence of glibenclamide (KATP channel blocker, 10 μM) or Nω-Nitro-L-arginine methyl ester (L-NAME: eNOS inhibitor, 100 μM) in the endothelium-intact aortic rings precontracted with potassium chloride (30 mM). Data were presented as means±SEM. Multiple comparisons of groups were performed by using ANOVA followed by post-hoc Bonferroni test. Results: Nebivolol elicited a concentration dependent vasorelaxant effect in the endothelium-intact aortic rings. Relaxant response to nebivolol was significantly inhibited by the presence of glibenclamide or L-NAME (p&amp;lt; 0.05). Although Emax values were not found significantly different among groups, pD2 values of nebivolol were reduced in the endothelium-intact aortic rings incubated with glibenclamide or L-NAME. Conclusion: These results demonstrate for the first time the involvement of KATP channels in the nebivolol-induced vasorelaxation in the endothelium-intact aorta precontracted with potassium chloride.

The hypertensive effect of sorafenib is abolished by sildenafil

BackgroundContrasting to the well documented tyrosine kinase inhibitor (TKI)-induced hypertension, little is known on their intrinsic vasomotor effects. We investigated the vasomotor effects of sorafenib, a widely used multikinase inhibitor in the treatment of hepatocellular and renal cell carcinoma and tested the hypothesis that sildenafil, a phosphodiesterase-5 (PDE-5) inhibitor, could represent a pharmacological strategy for the treatment of TKI-induced hypertension.MethodsConcentration-response curves of sorafenib were constructed in endothelium-intact or denuded precontracted rat aorta, in the presence or absence of several inhibitors. Acute intravenous effects of sorafenib on arterial blood pressure were also investigated in anaesthetized rats. Finally, rats were chronically treated with sorafenib during 4 weeks in the presence and absence of sildenafil.ResultsIn endothelium intact aortic ring, sorafenib induced a potent concentration-dependent relaxation of precontracted rat aorta. Removal of the endothelium shifted the concentration-response curve of sorafenib to the right and significantly reduced its maximal effects, demonstrating that sorafenib-induced vasorelaxation is endothelium-dependent and endothelium-independent. Inhibition of the different pathways implicated in the endothelium-dependent and independent vasorelaxation revealed that the endothelium-dependent effects of sorafenib result mainly from the activation of prostaglandin and the nitric oxide (NO) pathways. The endothelium-independent vasodilatory effects of sorafenib may result mainly from the activation of Na/K-ATPase and soluble guanylate cyclase. These vasodilatory effects observed in vitro were confirmed by the decrease in arterial blood pressure observed during acute administrations of sorafenib in anesthetized rats. Finally, and most importantly, we report here for the first time that chronic administration of sorafenib in rats induced an increase in SBP that was abolished by sildenafil.ConclusionThe multikinase inhibitor sorafenib induced in vitro vasorelaxation of large conductance artery, primary by activating soluble guanylate cyclase. Its chronic administration led to arterial blood hypertension that was counteracted by a PDE-5 inhibitor, sildenafil. Our results suggest that targeting the cGMP pathway including NO signalling might be an interesting pharmacological strategy for the treatment of TKI-induced hypertension.