Endothelium-dependent Vasorelaxant Effect Research Articles

In vitro biological activities of Calamintha nepeta L. aqueous extracts.

This study aimed to investigate the phenolic composition, antioxidant capacity, and toxicity of aqueous extracts of Calamintha nepeta L. leaves and their potential vasorelaxant effects. Aqueous extracts of Calamintha nepeta L. were prepared by three extraction methods: decoction, infusion, and maceration. The total phenolic contents of the extracts and their antioxidant properties were investigated. The toxicity was evaluated by Artemia salina lethality bioassay. The decoction extract was analyzed by HPLC for its chemical profile and was also used to evaluate the vasorelaxant effect on thoracic aortic rings isolated from healthy Sprague Dawley rats. Pre-contraction was induced by phenylephrine, followed by cumulative doses of the extract (0.001 up to 250 µg/ml). Aqueous extracts of Calamintha nepeta L. showed noticeable radical scavenging and chelating activities. However, the decoction extract exhibited the most powerful antioxidant capacity. No toxicity was recorded for the extracts obtained by decoction and infusion. Caffeic acid, quercetin, and rosmarinic acid were the main identified compounds. Notably, the aqueous extract obtained by decoction induced significant relaxation in endothelium-intact aortic rings at lower concentrations, and at higher concentrations in denuded aortic rings. This study reveals that Calamintha nepeta L. extracted with a decoction method possesses potent antioxidant capacity and has an endothelium-dependent vasorelaxant effect.

Blood-Pressure-Lowering and Endothelium-Dependent Vasorelaxant Effects of Nutgall Tree in Rats.

Hypertension is the crucial modifiable risk factor for cardiovascular diseases, and efforts to identify functional foods that are effective for hypertension control are increasing. The nutgall tree (NT, Rhus chinensis Mill.) is used in traditional medicine and food because of its medicinal value. However, the role of NT in hypertension has not been investigated. Therefore, the hypotensive effect of NT leaf ethanol extract (NTE) was investigated in spontaneously hypertensive rats (SHRs). SHRs were allocated to three groups (control, 300, or 1000 mg/kg NTE), and blood pressure was measured before and after oral administration. Systolic and diastolic blood pressure significantly decreased in the NTE 1000 mg/kg group and was the lowest at 2 h after administration (-26.4 ± 10.3, -33.5 ± 9.8%, respectively). Daily NTE administration for five days also resulted in a similar effect. Further, the vasorelaxant effects and related mechanisms were investigated in the aortas of Sprague Dawley rats. NTE showed the dose-dependent blood-vessel-relaxing effect, and its mechanism involves the NO-sGC-cGMP pathway, activation of K+ channels, and reduction in the vasoconstrictive action of angiotensin II. Therefore, our study provides basic data indicating the potential use of NTE as a functional food for high blood pressure.

Hypotensive and Endothelium-Dependent Vasorelaxant Effects of Grayblue Spicebush Ethanol Extract in Rats.

Hypertension is one of the most common chronic diseases, and its prevalence is increasing worldwide. Lindera glauca (Siebold & Zucc.) Blume, known as grayblue spicebush (GS), has been used as food and for medicinal purposes; however, studies about its hypotensive or vasorelaxant effects are lacking. Therefore, the hypotensive effect of an ethanolic extract of the GS branch (GSE) was investigated in 15-week-old spontaneously hypertensive rats (SHRs) using the tail cuff method. The GSE administration group (1000 mg/kg SHR body weight) showed a decrease in their systolic and diastolic blood pressure measured 4 h after its administration. In addition, we investigated its vasorelaxant effect using the thoracic aorta dissected from Sprague-Dawley rats. The GSE (0.5, 1, 2, 5, 10, and 20 μg/mL) showed an endothelium-dependent vasorelaxant effect, and its mechanisms were found to be relevant to the inward rectifier, voltage-dependent, and non-selective K+ channels. Moreover, the GSE (20 μg/mL) showed an inhibitory effect on aortic rings constricted with angiotensin II. Considering its hypotensive and vasorelaxant effects, GSE has potential as a functional food to help treat and prevent high blood pressure. However, further studies on the identification of the active components of GSE and safety evaluations of its use are needed.

Vascular Relaxation and Blood Pressure Lowering Effects of Prunus mume in Rats.

Prunus mume Siebold et Zuccarini is mainly consumed as processed fruits in beverages, vinegar, alcohol, or fruit syrup; studies have reported various functional effects. Many pharmacological and functional studies exist on fruit extracts or processed foods using fruits, however, efficacy studies on various parts of P. mume, including the bark, branches, flowers, and leaves, have not been sufficiently conducted. A previous study revealed that a 70% ethanol extract of P. mume branches induced vascular endothelium-dependent vasorelaxant effects in rat thoracic aortic rings. Therefore, we hypothesized that various parts (the fruits, flowers, leaves, and bark) might have vasorelaxant effects. We evaluated the effects of P. mume extracts on the vascular relaxation of isolated rat thoracic aorta and hypotensive effects in spontaneous hypertensive rats (SHR). A 70% ethanol extract of P. mume bark (PBaE) was the most effective, thus, we investigated its vasorelaxant mechanisms and hypotensive effects. PBaE lowered the blood pressure in SHR and induced the vascular endothelium-dependent relaxation of isolated rat aortic rings via the NO/sGC/cGMP and the PGI2 pathways in the vascular smooth muscle. Potassium channels, such as KCa, KATP, KV, and Kir, were partially associated with a PBaE-induced vasorelaxation. Therefore, PBaE might help prevent and treat hypertension.

Therapeutic Benefits of Pomegranate Flower Extract: A Novel Effect That Reduces Oxidative Stress and Significantly Improves Diastolic Relaxation in Hyperglycemic In Vitro in Rats.

The pomegranate flower is an ancient herb in traditional Chinese medicine with multiple properties. Recent studies have shown that pomegranate flower extract is beneficial, especially for hyperglycemia. In this experiment, we investigated the diastolic effect of pomegranate flower polyphenol (PFP) extract on the isolated thoracic aorta of rats in both the absence and presence of high glucose levels. Isotonic contractile forces were recorded from aortic rings (about 3 mm in length) from rats using the BL-420F Biological Function Test System. Tissues were precontracted with 60 mM KCl to obtain maximum tension under 1.0 g load for 1 hour before the balance was achieved, and the fluid was changed every 15 minutes. PFP (700 mg/L–900 mg/L) showed a concentration-dependent relaxant effect on the aortic rings; vasodilation in the endothelium-intact was significantly higher than that in the de-endothelialized segments (P < 0.01). The endothelium-dependent vasorelaxant effect of PFP was partially attenuated by K+ channel blockers, tetraethylammonium (TEA), glibenclamide (Glib), and BaCl2, as well as L-NAME (eNOS inhibitor) on the denuded endothelium artery ring. Concentration-dependent inhibition of PFP on releasing intracellular Ca2+ in the Ca2+-free solution and vasoconstriction of CaCl2 in Ca2+-free buffer plus K+ (60 mM) was observed. In addition, PFP (0.1–10 mg/L) showed significant inhibition of acetylcholine-induced endothelial-dependent relaxation in the aorta of rats in the presence of high glucose (44 mmol/L). Nevertheless, the vasodilating effect of PFP was inhibited by atropine and L-NAME. The results indicated that PFP-induced vasodilation was most likely related to the antioxidant effects through enhanced NO synthesis, as well as the blocking of K+ channels and inhibition of extracellular Ca2+ entry. In conclusion, these observations showed that PFP ameliorates vasodilation in hyperglycemic rats. Hence, our results suggest that PFP supplementation may be beneficial for hypertensive patients with diabetes.

Cardioprotective Effect of Rumex vesicarius Linn. Leaf Extract against Catecholamine-Induced Cardiotoxicity.

Rumex vesicarius (L.) is a folklore medicinal herb that has been used for centuries to cure cardiovascular diseases. The present work was carefully designed to ascertain the pharmacological basis for R. vesicarius’s therapeutic efficacy in cardiovascular diseases, as well as the underlying mechanism. In the ex vivo investigation, the aqueous-methanolic leaf extract of R. vesicarius was shown to have endothelium-dependent vasorelaxant effects in rabbit aorta tissue preparations, and its hypotensive responses were quantified by pressure and force transducers coupled to the Power Lab Data Acquisition System. Furthermore, when rabbits were subjected to adrenaline-induced myocardial infarction, R. vesicarius demonstrated cardioprotective characteristics. In contrast to the intoxicated group, the myocardial infarction model showed lower ALP, CK-MB, CRP, LDH, ALT, troponin, and AST levels (p > 0.005–0.000), as well as edema, necrosis, apoptosis, inflammatory cell enrolment, and necrosis. R. vesicarius exhibited significant antioxidant activity and delayed noradrenaline-induced platelet aggregation. Its cardioprotective, anticoagulant, and vasorelaxant properties in both investigations (in vivo and ex vivo) are mediated through partial endothelium-dependent, NO and calcium channel blockade mediated vasorelaxation. The minimizing of adrenaline, oxidative stress, and tissue damage demonstrate its therapeutic efficacy in cardiovascular diseases.

Vasorelaxant effect of curcubisabolanin A isolated from Curcuma longa through the PI3K/Akt/eNOS signaling pathway

Ethnopharmacological relevanceCurcuma longa L. (Zingiberaceae) is a known blood-activating and stasis-removing traditional Chinese medicine and has relevant pharmacological properties. The rhizomes of C. longa have been used for the treatment of cardiovascular disease (CVD) in China. Previous studies have shown that sesquiterpenoids from C. longa have significant vasorelaxant effects, which are closely associated with the prevention and treatment of CVD. Aim of the studyTo explore the sesquiterpenoids with vasorelaxant effects from C. longa and investigate the underlying mechanisms. Materials and methodsThe compound was isolated from C. longa by multiple chromatography technologies. Its structure was determined by extensive spectroscopic analyses, nuclear magnetic resonance (NMR) data calculations, electronic circular dichroism (ECD) data calculations, and optical rotation (OR) data calculations. The vasorelaxant effect of the isolated compound was evaluated by KCl- or phenylephrine (PHE)-inducing contraction of the rat thoracic aortic rings. Endothelial removal and L-NAME pretreatment experiments were used to verify the endothelium-dependent vasorelaxant effect of the isolated compound in rat thoracic aortic rings. NO production was monitored in human umbilical vein endothelial cells (HUVECs). Western blot was carried out in HUVECs to elucidate the potential mechanisms. ResultsA new bisabolane-type sesquiterpenoid, curcubisabolanin A [(+)-(1S,7S,9E)-bisabola-2(3),4(15),9(10)-trien-11-ol], was isolated from the rhizomes of C. longa. curcubisabolanin A exhibited endothelium-dependent relaxation on rat thoracic aortic rings, while pre-treatment of intact aortic rings with an eNOS inhibitor (L-NAME) attenuated the vasorelaxant response of curcubisabolanin A. In addition, curcubisabolanin A induced intracellular NO production and significantly increased the levels of phosphorylated PI3K (p-PI3K), phosphorylated Akt (p-Akt), and phosphorylated eNOS (p-eNOS) in HUVECs. LY294002 (a blocker of PI3K) and MK-2206 (a highly selective inhibitor of Akt) significantly decreased these effects of curcubisabolanin A. ConclusionsThese findings demonstrated that the vasorelaxant effect of curcubisabolanin A was partially endothelium-dependent and was related to regulation of NO production in vascular endothelial cells through the PI3K/Akt/eNOS signaling pathway.

Endothelium-dependent vasorelaxant effects of praeruptorin a in isolated rat thoracic aorta

ABSTRACT Praeruptorin A (PA) is a natural coumarin compound from the roots of Radix Peucedani and is commonly used in the treatment of certain respiratory diseases and hypertension. Although previous studies identified relaxant effects of PA on tracheal and arterial preparations, little is known about its vasodilative effects and underlying mechanisms. Here, an organ bath system and tension recording methods were used to prepare and analyze isolated rat thoracic aorta artery rings. Aorta artery rings were pre-contracted with phenylephrine and then incubated with PA, and the possible mechanism of relaxation was investigated by adding inhibitors of nitric oxide synthase (NG-nitro-L-arginine methyl ester, L-NAME), endothelial nitric oxide synthase (L-NG-nitroarginine, L-NNA), cyclooxygenase (indomethacin), guanylyl cyclase (1 H-[1,2,4]oxadiazolo [4,3-a]quinoxalin-1-one, ODQ), and KCa channels (tetraethylammonium, TEA). Our study showed that PA-induced vasodilation was blocked by L-NAME, L-NNA, and ODQ, while CaCl2-induced vasoconstriction was countered by PA. Thus, PA may exert a vasodilatory effect by influencing the amounts of endothelium-derived relaxing factors through endothelial-dependent NO-cGMP and prostacyclin pathways (such as NO and prostacyclin 2). In the rat thoracic aorta, PA reduces vasoconstriction by inhibiting Ca2+ inflow.

Taxifolin as a Major Bioactive Compound in the Vasorelaxant Effect of Different Pigmented Rice Bran Extracts.

Cardiovascular disease is one of the leading causes of morbidity and mortality in recent years. The intake of polyphenol rich diets has been associated with improved cardiovascular function and reduced cardiovascular risks. Oryza sativa L. is one of the most common cereals worldwide. Rice bran, a byproduct of the rice milling process, contains many bioactive ingredients, including polyphenols, polysaccharides, proteins, and micronutrients. It is also consumed as a healthy diet in the form of rice bran oil and powder in many Asian countries like Japan, South Korea, and India for its several health benefits as a natural antioxidant. Thus, this study evaluated the vasorelaxant effect of ethanolic extracts of brown, green, red, and black rice bran and investigated its underlying vasorelaxant mechanism. Among the four rice bran extracts (RBEs) examined, the red rice bran extract (RRBE) had a strong endothelium-dependent vasorelaxant effect, which was markedly prevented by N-ω-nitro-L-arginine [endothelial nitric oxide synthase (eNOS) inhibitor], wortmannin [phosphoinositide-3 kinase (PI3K) inhibitor], and 1H-[1,2,4]oxadiazole[4,3-alpha]quinoxalin-1-one (inhibitor of guanylate cyclase). Likewise, RRBE induced the phosphorylation of eNOS and Src in cultured endothelial cells, thereby stimulating NO formation. Altogether, these findings propose that RRBE induces endothelium-dependent relaxation, involving at least in part, NO-mediated signaling through the PI3K/eNOS pathway. Further, LC-PDA analysis conducted on the four RBEs also revealed that RRBE highly contained taxifolin, which is an active flavanonol that induces endothelium-dependent vasorelaxation, compared to other RBEs. Subsequently, the underlying mechanism of taxifolin was assessed through vascular reactivity studies with pharmacological inhibitors similar to that of RRBE. These findings deciphered a distinct difference in vasorelaxant effects between RRBE and the other RBEs. We also observed that RRBE induced a potent endothelium-dependent NO-mediated relaxation in coronary artery rings, which involved the Src/PI3K pathway that activates eNOS. Additionally, taxifolin exhibited, at least in part, similar vasoprotective effects of RRBE. Therefore, we propose that RRBE may serve as natural sources of functional phytochemicals that improve cardiovascular diseases associated with disturbed NO production and endothelial dysfunction.

Vasorelaxant and Antioxidant Effects of Aframomum pruinosum Gagnep. (Zingiberaceae) Seed Extracts May Mediate Their Cardioprotective Activity against Isoproterenol-Induced Myocardial Infarction.

Aframomum pruinosum seeds are traditionally used in Cameroon to treat cardiac palpitations. The present work evaluates the cardioprotective effects of the aqueous (AE) and ethanolic (EE) extracts from A. pruinosum seeds against isoproterenol-induced myocardial infarction. Male Wistar rats were pretreated for 14 days with AE or EE at doses of 75 and 150 mg/kg/day or propranolol (10 mg/kg/day). On days 15 and 16, they were injected subcutaneously with isoproterenol (85 mg/kg/day). Blood pressure and heart rate were weekly recorded by tail-cuff plethysmography during pretreatment and 24 hours after the second dose of isoproterenol. At the end of the treatment period, serum Lactate Dehydrogenase (LDH), Alanine Aminotransferase (ALT), Aspartate Aminotransferase (AST), cardiac nitric oxide (NO), myeloperoxidase (MPO), and oxidative stress parameters (SOD, catalase, MDA, and GSH) were assayed. Sections of left ventricle tissue were subjected to histological analysis. The vasorelaxant effects of cumulative concentrations of AE or EE (3–300 µg/mL) were evaluated on intact or endothelium-denuded isolated aorta rings precontracted with noradrenaline (1 µM). The vasorelaxant effects of the plant extracts were also tested in the presence of Nω-nitro-L-arginine methyl ester (L-NAME; 100 µM). AE and EE significantly prevented blood pressure decrease and heart rate increase elicited by isoproterenol. Both plant extracts inhibited the increase in ALT, AST, NO, and MPO but did not prevent LDH surge. Oxidative stress parameters were improved following A. pruinosum pretreatment. AE and EE highly reduced cardiomyocyte necrosis and fibrosis but did not prevent leukocyte infiltration. Both extracts induced a concentration-dependent vasorelaxation that was significantly inhibited by the destruction of the endothelium and by L-NAME. Extracts of A. pruinosum exhibited cardioprotective effects, and EE was the most active. The cardioprotective effects of A. pruinosum extracts could be ascribed to their antioxidant, antinecrotic, and endothelium-dependent vasorelaxant effects.

Piper tectoniifolium Kunth: A New Natural Source of the Bioactive Neolignan (-)-Grandisin.

The Piper species are a recognized botanical source of a broad structural diversity of lignans and its derivatives. For the first time, Piper tectoniifolium Kunth is presented as a promising natural source of the bioactive (−)-grandisin. Phytochemical analyses of extracts from its leaves, branches and inflorescences showed the presence of the target compound in large amounts, with leaf extracts found to contain up to 52.78% in its composition. A new HPLC-DAD-UV method was developed and validated to be selective for the identification of (−)-grandisin being sensitive, linear, precise, exact, robust and with a recovery above 90%. The absolute configuration of the molecule was determined by X-ray diffraction. Despite the identification of several enantiomers in plant extracts, the major isolated substance was characterized to be the (−)-grandisin enantiomer. In vascular reactivity tests, it was shown that the grandisin purified from botanical extracts presented an endothelium-dependent vasorelaxant effect with an IC50 of 9.8 ± 1.22 μM and around 80% relaxation at 30 μM. These results suggest that P. tectoniifolium has the potential to serve as a renewable source of grandisin on a large scale and the potential to serve as template for development of new drugs for vascular diseases with emphasis on disorders related to endothelial disfunction.

Endothelium-dependent and endothelium-independent vasorelaxant effects of unripe Rubus coreanus Miq. and Dendropanax morbiferus H. L\xe9v. extracts on rat aortic rings

BackgroundMany clinical trials on antihypertensive drugs have confirmed the usefulness of these drugs in regulating blood pressure effectively. However, all the drugs usually require long-term use; thus, economic burdens as well as some adverse effects, including headache, diarrhea, skin rash, edema, fever, and liver and kidney dysfunction, accompany their use. Therefore, we attempted to identify natural medications for treating hypertension. We investigated the antihypertensive effects of Dendropanax morbiferus H. Lév. extract (DP), enzymatically hydrolyzed DP extract (Hy-DP) and 5% unripe Rubus coreanus Miq. ethanol extract (5-uRCK).MethodsExtracts of the unripe R. coreanus were made using 20 volumes of 5% ethanol at 100 °C for 4 h. The dried leaves of D. morbiferus were subjected to enzymatic hydrolysis by protease, trypsin, bromelain and papain to increase L-arginine and GABA levels. Vasorelaxant effects of these extracts were evaluated on rat aorta precontracted with phenylephrine. In addition, hippocampal neurons, RAW 264.7 macrophages and human umbilical vein endothelial cells (HUVECs) were used to exam nitric oxide (NO) production and NO synthase (NOS) gene expression.ResultsDP, Hy-DP and 5-uRCK dose-dependently relaxed isolated rat aortic rings contracted with phenylephrine; however, Hy-DP was more effective than DP. L-NAME and ODQ differentially inhibited Hy-DP- and 5-uRCK-induced relaxation; both L-NAME and ODQ completely blocked 5-uRCK-mediated relaxation. Endothelium-denuded aortic ring relaxation was induced much less by 5-uRCK than by Hy-DP. Therefore, 5-uRCK and Hy-DP induced vascular relaxation by endothelium-dependent and partially endothelium-dependent mechanisms, respectively. Hy-DP and 5-uRCK induced eNOS gene expression and NO production in endothelial cells but did not change iNOS/nNOS expression or NO production in macrophages or neuronal cells. Both Hy-DP and 5-uRCK effectively induced vascular relaxation via similar but slightly different mechanisms. The best effective combination was investigated after mixing Hy-DP and 5-uRCK at different ratios. The 2:1 Hy-DP:5-uRCK mixture inhibited ACE, cGMP- and cAMP-dependent phosphodiesterase activity and vascular relaxation better than the other mixtures.ConclusionIn conclusion, Hy-DP and 5-uRCK exert antihypertensive effects through different endothelium-dependent or endothelium-independent mechanisms. These findings may greatly help elucidate the mechanisms of clinical efficacy of Hy-DP:5-uRCK mixtures used for blood pressure regulation.

P1530Vasorelaxation as a mechanism of procyanidin B2 cardioprotective effect

Abstract Introduction Findings from epidemiological studies indicate that polyphenols, widespread in human diet and with numerous biological activities, act cardioprotectively. Procyanidins are subclass of polyphenols with high content in commonly consumed foods and beverages, such as grapes, tea, chocolate, nuts and apples. Cardioprotective abilities of procyanidins, might, at least in part, attribute to their vasodilator properties. Purpose Because the exact mechanisms by which procyanidin B2 causes vasorelaxation are unclear, we aimed to investigate relaxant effect of procyanidin B2 on the isolated human internal mammary artery (HIMA) and its underlying mechanisms. Methods The HIMA segments were collected from patients suffering from coronary artery disease who were undergoing coronary artery bypass surgery and studied in organ bath. Results Procyanidin B2 induced strong concentration-dependent relaxation of HIMA rings pre-contracted by phenylephrine. Pretreatment with L-NAME, a NO synthase inhibitor, hydroxocobalamin, a NO scavenger, and ODQ, an inhibitor of soluble guanylate cyclase, significantly inhibited procyanidin B2-induced relaxation of HIMA, while indomethacin, a cyclooxygenase inhibitor, considerably reduced effects of low concentrations. Among K+ channel blockers, iberiotoxin, a selective blocker of large conductance Ca2+-activated K+ channels (BKCa), abolished procyanidin B2-induced relaxation, glibenclamide, a selective ATP-sensitive K+ (KATP) channel blocker, induced partial inhibition, while 4-aminopyridine, a blocker of voltage-gated K+ (KV) channels, and TRAM-34, an inhibitor of intermediate-conductance Ca2+-activated K+ (IKCa) channels, slightly reduced maximal relaxation of HIMA. Conclusion Our results demonstrate that, in HIMA, procyanidin B2 produces strong endothelium-dependent vasorelaxant effect. It seems that this relaxation is primarily the result of an increased NO synthesis and secretion by endothelial cells and partially of prostacyclin, although it involves activation of BKCa and KATP, as well as KV and IKCa channels in high concentrations of procyanidin B2. Acknowledgement/Funding The study was supported by a Scientific Research Grant (P175088) from Ministry of Science and Technology Serbia.

Endothelium-Dependent Vasorelaxant Effect of Prunus Persica Branch on Isolated Rat Thoracic Aorta

Peach (Prunus persica (L.) Batsch) is a popular fruit consumed by people worldwide, owing to its pleasant flavor and high mineral nutrient content. A few plants from the genus Prunus, such as Prunus yedoensis, Prunus cerasus, and Prunus serotina have shown vasorelaxant and vasodilatory effects, to date, no study has investigated the vasorelaxation effects of the P. persica branch extract (PPE). The vasorelaxant effect of PPE was endothelium-dependent, and it was related to the NO-sGC-cGMP, vascular prostacyclin, and muscarinic receptor transduction pathway. K+ channels, such as the BKCa, KV, and KATP channels, were partially associated with PPE-induced vasorelaxation. PPE was effective in relaxing serotonin (5-HT)- or angiotensin II-induced contraction; furthermore, PPE attenuated Ca2+-induced vasoconstriction by IP3 receptors in the SR membrane, but its vasorelaxant effect was not associated with the influx of extracellular Ca2+ via receptor-operative Ca2+ channels or voltage-dependent Ca2+ channels. Recognizing the rising use of functional foods for hypertension treatment, our findings imply that PPE may be a natural antihypertensive agent.

Mechanisms involved in the endothelium-dependent vasodilatory effect of an ethyl acetate fraction of Cyathea phalerata Mart. in isolated rats’ aorta rings

The species Cyathea phalerata Mart. is a tree fern, commonly known as “xaxim”, which is found in tropical and subtropical areas of Brazil. The present study investigated the mechanisms related with the vasorelaxant effects of an Ethyl Acetate Fraction (EAF) obtained from C. phalerata in rats’ thoracic aorta rings. In pre-contracted vessels, EAF (0.1–1000 μg/mL) caused a concentration-dependent relaxation. The endothelium denudation, the nitric oxide (NO) synthase and guanylyl cyclase inhibitor reduced the vasodilation, indicating the participation of NO/cGMP pathway in its effect. The relaxation of EAF was abolished in the absence of extracellular Ca2+ and was significantly decreased in the presence of Ca2+ entry blocker, suggesting that Ca2+ influx plays an important role in EAF effect and probably in eNOS activity. However, the PI3K/Akt pathway is not responsible for eNOS phosphorylation/activation. The vasodilator effect of EAF was partially inhibited by KCl 40 mM and almost totally abolished with L-NOARG + KCl 40 mM, indicating also the role of hyperpolarization in its effect. Calcium activated K+ channels are not involved in the EAF-induced hyperpolarization. The COX inhibitor, indomethacin, slightly reduced the vasodilation induced by EAF. In addition, EAF did not alter the relaxant effects of NO-donor, indicating that the relaxant activity cannot be attributed to free radical-scavenging properties. In conclusion, the present study showed that the EAF, causes an endothelium-dependent vasorelaxant effect in aorta that mainly involves the NO-cGMP pathway, hyperpolarization and prostanoids. The vasorelaxant activity of EAF can be attributed to the occurrence of polyphenol compounds.

Endothelium-dependent and endothelium-independent vasorelaxant effects of tiliacorinine 12′-O-acetate and mechanisms on isolated rat aorta

Tiliacorinine 12′-O-acetate is a modified analog of Tiliacorinine, a major compound in Tiliacora triandra. The present study explored the vasorelaxation property of tiliacorinine 12′-O-acetate and its mechanism in isolated rat aorta using the organ bath technique. Tiliacorinine 12′-O-acetate exhibited concentration-dependent (10−15–10−3.5 M) vasorelaxation in endothelium-intact rings (Emax = 93.53 ± 2.79%) and endothelium-denuded rings (Emax = 74.31 ± 5.09%). The effects of tiliacorinine 12′-O-acetate were attenuated by pre-incubation with N(ω)-nitro-l-arginine methyl ester (L-NAME, endothelium nitric oxide synthase inhibitor) (100 μM), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, soluble quanylylcyclase inhibitor) (1 μM), and 4-aminopyridine (1 mM, Kv channel blocker). However, this effect was not impacted by indomethacin (10 μM, cyclooxygenase inhibitor), tetraethylammonium (5 mM, Kca channel blocker), barium chloride (1 mM, KIR channel blocker), or glibenclamide (10 μM, KATP channel blocker). Moreover, pretreatment with tiliacorinine 12′-O-acetate reduced the effect of L-NAME (100 μM) on acetylcholine-induced vasorelaxation. Tiliacorinine 12′-O-acetate showed inhibitory effects on CaCl2-induced contracted rings and reduced the contraction induced by phenylephrine (10 μM) and caffeine (20 mM) in a Ca2+-free solution. The results of this study suggest that tiliacorinine 12′-O-acetate induced endothelium-dependent vasorelaxation through the eNOS/NO/sGC pathway, and also induced endothelium independent vasorelaxation involving the modulation of sGC activity, Kv channels, Ca2+ influx through Ca2+ channels and intracellular Ca2+ release. The data concerning the benefits of tiliacorinine 12′-O-acetate might be further investigated for the application of tiliacorinine 12′-O-acetate as an antihypertensive compound.

The cAMP effectors PKA and Epac activate endothelial NO synthase through PI3K/Akt pathway in human endothelial cells

3′,5′-Cyclic adenosine monophosphate (cAMP) exerts an endothelium-dependent vasorelaxant action by stimulating endothelial NO synthase (eNOS) activity, and the subsequent NO release, through cAMP protein kinase (PKA) and exchange protein directly activated by cAMP (Epac) activation in endothelial cells. Here, we have investigated the mechanism by which the cAMP-Epac/PKA pathway activates eNOS. cAMP-elevating agents (forskolin and dibutyryl-cAMP) and the joint activation of PKA (6-Bnz-cAMP) and Epac (8-pCPT-2′-O-Me-cAMP) increased cytoplasmic Ca2+ concentration ([Ca2+]c) in ≤30% of fura-2-loaded isolated human umbilical vein endothelial cells (HUVEC). However, these drugs did not modify [Ca2+]c in fluo-4-loaded HUVEC monolayers. In DAF-2-loaded HUVEC monolayers, forskolin, PKA and Epac activators significantly increased NO release, and the forskolin effect was reduced by inhibition of PKA (Rp-cAMPs), Epac (ESI-09), eNOS (L-NAME) or phosphoinositide 3-kinase (PI3K; LY-294,002). On the other hand, inhibition of CaMKII (KN-93), AMPK (Compound C), or total absence of Ca2+, was without effect. In Western blot experiments, Serine 1177 phosphorylated-eNOS was significantly increased in HUVEC by cAMP-elevating agents and PKA or Epac activators. In isolated rat aortic rings LY-294,002, but not KN-93 or Compound C, significantly reduced the vasorelaxant effects of forskolin in the presence of endothelium. Our results suggest that Epac and PKA activate eNOS via Ser 1177 phosphorylation by activating the PI3K/Akt pathway, and independently of AMPK or CaMKII activation or [Ca2+]c increase. This action explains, in part, the endothelium-dependent vasorelaxant effect of cAMP.

Endothelium-dependent vasorelaxant effect of procyanidin B2 on human internal mammary artery

The aim of the present study was to investigate and characterize vasorelaxant effect of procyanidin B2 on human internal mammary artery (HIMA) as one of the mechanisms of its protective effect against vascular risk. Procyanidin B2 induced strong concentration-dependent relaxation of HIMA rings pre-contracted by phenylephrine. Pretreatment with L-NAME, a NO synthase inhibitor, hydroxocobalamin, a NO scavenger, and ODQ, an inhibitor of soluble guanylate cyclase, significantly inhibited procyanidin B2-induced relaxation of HIMA, while indomethacin, a cyclooxygenase inhibitor, considerably reduced effects of low concentrations. Among K+ channel blockers, iberiotoxin, a selective blocker of large conductance Ca2+-activated K+ channels (BKCa), abolished procyanidin B2-induced relaxation, glibenclamide, a selective ATP-sensitive K+(KATP) channels blocker, induced partial inhibition, while 4-aminopyridine, a blocker of voltage-gated K+(KV) channels, and TRAM-34, an inhibitor of intermediate-conductance Ca2+-activated K+(IKCa) channels, slightly reduced maximal relaxation of HIMA. Further, procyanidin B2 relaxed contraction induced by phenylephrine in Ca2+-free Krebs solution, but had no effect on contraction induced by caffeine. Finally, thapsigargin, a sarcoplasmic reticulum Ca2+-ATPase inhibitor, significantly reduced relaxation of HIMA produced by procyanidin B2. These results demonstrate that procyanidin B2 produces endothelium-dependent relaxation of HIMA pre-contracted by phenylephrine. This effect is primarily the result of an increased NO synthesis and secretion by endothelial cells and partially of prostacyclin, although it involves activation of BKCa and KATP, as well as KV and IKCa channels in high concentrations of procyanidin B2.

Aged garlic extract exerts endothelium-dependent vasorelaxant effect on rat aorta by increasing nitric oxide production

BackgroundClinical trials have shown that aged garlic extract (AGE) is effective in reducing blood pressure of hypertensive patients. However, the mechanisms involved remain to be elucidated. PurposeThe aim of the present study was to investigate the vasorelaxant effect of AGE on the aorta and its mechanism of action in order to clarify the blood pressure-lowering action of AGE. MethodsThe vasorelaxant effect was evaluated in isolated rat aortic rings. After aortic rings were contracted by 3 × 10−6M norepinephrine (NE) for 30min, AGE and other test drugs were added to the aortic rings. All results were expressed as percentages of the maximal NE-induced contraction. ResultsAGE induced the concentration–dependent vasorelaxation of isolated rat aortic rings that had been precontracted with norepinephrine. The effect of AGE was severely impaired in aortic rings lacking endothelium. In addition, the effect of AGE was inhibited by a nitric oxide synthase (NOS) inhibitor and a nitric oxide (NO) scavenger. Moreover, AGE treatment of aorta significantly increased the NO production. When various constituents of AGE were tested, the vasorelaxation of aorta was observed only in the presence of L-arginine, a substrate of NOS. ConclusionAGE causes endothelium-dependent vasorelaxation of aorta via stimulation of NO production and that L-arginine in AGE serves as a key agent for NOS-mediated NO production.

Involvement of endothelium in the vasorelaxant effects of 3,4-DHPEA-EA and 3,4-DHPEA-EDA, two major functional bioactives in olive oil

The olive oil polyphenols 3,4-DHPEA-EA and 3,4-DHPEA-EDA displayed an endothelium-dependent vasorelaxant effect in rat aorta, starting at ~1 µM and abolished by NG-nitro-L-arginine (L-NA) or N-acetylcysteine, and an endothelium-independent vasorelaxant effect, starting at ~10 µM. Hydroxytyrosol only presented an endothelium-independent effect at 100 µM. DHPEA-EA and 3,4-DHPEA-EDA, but not hydroxytyrosol, also increased NO generation within endothelial cells. At higher concentrations, the three compounds reduced arginine-vasopressin-induced increase of cytosolic Ca2+ concentration ([Ca2+]c) in vascular myocytes. By UV-visible spectroscopy, we found that these polyphenols undergo autoxidative processes in organ-bath conditions. Thus, 3,4-DHPEA-EA and 3,4-DHPEA-EDA have an endothelium-dependent vasorelaxant effect caused by an enhanced NO production, probably through a redox mechanism within endothelial cells and an endothelium-independent vasorelaxant effect mediated by a reduction of agonist-induced [Ca2+]c increase in vascular myocytes. Bearing in mind the plasmatic concentrations of these polyphenols following dietary intake of olive oil, these effects could modulate vascular tone in vivo.