Effects of flavonoids on rat aortic smooth muscle contractility: structure-activity relationships

The Vascular Effects of Isolated Isoflavones-A Focus on the Determinants of Blood Pressure Regulation

Isoflavones are phytoestrogen compounds with important biological activities, including improvement of cardiovascular health. This activity is most evident in populations with a high isoflavone dietary intake, essentially from soybean-based products. The major isoflavones known to display the most important cardiovascular effects are genistein, daidzein, glycitein, formononetin, and biochanin A, although the closely related metabolite equol is also relevant. Most clinical studies have been focused on the impact of dietary intake or supplementation with mixtures of compounds, with only a few addressing the effect of isolated compounds. This paper reviews the main actions of isolated isoflavones on the vasculature, with particular focus given to their effect on the determinants of blood pressure regulation. Isoflavones exert vasorelaxation due to a multitude of pathways in different vascular beds. They can act in the endothelium to potentiate the release of NO and endothelium-derived hyperpolarization factors. In the vascular smooth muscle, isoflavones modulate calcium and potassium channels, leading to hyperpolarization and relaxation. Some of these effects are influenced by the binding of isoflavones to estrogen receptors and to the inhibition of specific kinase enzymes. The vasorelaxation effects of isoflavones are mostly obtained with plasma concentrations in the micromolar range, which are only attained through supplementation. This paper highlights isolated isoflavones as potentially suitable alternatives to soy-based foodstuffs and supplements and which could enlarge the current therapeutic arsenal. Nonetheless, more studies are needed to better establish their safety profile and elect the most useful applications.

Underlying mechanism of vasorelaxant effect exerted by 3,5,7,2',4'-pentahydroxyflavone in rats aortic ring

Morin (3,5,7,2',4'-pentahydroxyflavone) is a yellow coloured natural flavonoid found in plants of the Moraceae family. This favonoid is easily sources from readily available fruits, vegetables and eve certain beverages. Among the sources that was identified, it is clear that morin is most abundantly found in almond, old fustic, Indian guava, and Osage orange. Multiple studies have suggested that morin has multiple therapeutic actions and possess potential to be a functional potent drug. Previous studies demonstrated that morin is capable of resolving deoxycorticosterone acetate-salt-induced hypertension and possess strong vasorelaxant properties. However, the exact mechanisms remains unknown. Therefore, this study is designed to investigate the in vitro mechanism of morin-induced vasorelaxant effects. The underlying mechanisms of morin's vasorelaxant activities were evaluated on thoracic aortic rings isolated from Sprague-Dawley rats. Results from the study demonstrated morin causing vasodilatory reaction in phenylephrine and potassium chloride pre-contracted endothelium-intact aortic rings with the effect being significantly affected in endothelium-denuded aortic rings. Pre-incubation of the aortic rings with ODQ (selective cGMP-independent sGC inhibitor), indomethacin (nonselective COX inhibitor), L-NAME (endothelial nitric oxide inhibitor), propranolol (β₂-adrenegic receptors blocker), and atropine (muscarinic receptors blocker) significantly reduced the vasorelaxant effect of morin. It was also found to be able to reduce the intracellular calcium level by blocking VOCC and calcium intake from the extracellular environment and the intracellular release of calcium from the sarcoplasmic reticulum. The present study showed that the vasorelaxant effect of morin potentially involves the NO/sGC, muscarinic receptors, β₂-adrenegic receptors, and calcium channels.

Novel potent vasodilating agents: Evaluation of the activity and potency of LINS01005 and derivatives in rat aorta

Cardiovascular diseases (CVDs) present high prevalence rates in the current world. It is estimated that approximately one-third of the global deaths are related to CVDs, and thus there is still a need for novel drugs to treat these disorders. We serendipitously discovered that LINS01005 (5a) is a potent vasodilating agent in rat aorta, and therefore a set of analogues were evaluated for the vasodilating potency in Wistar and SHR rat thoracic aorta precontracted with norepinephrine, with endothelium intact (E+) or denuded (E-) aortic rings. Compounds 5a and 5b were the most potent, showing submicromolar potency for endothelium intact vessels (EC₅₀ 853 and 941 nM, respectively) and micromolar values for E- vessels (EC₅₀ 2.4 and 7.1 µM, respectively). These compounds were indeed significantly more potent vasodilating agents in SHR-derived aortic rings (p < 0.001), showing nanomolar potency for 5a [EC₅₀ 2.4 nM (E+) 9.0 nM (E-)] and 5b [EC₅₀ 20 nM (E+) 2.1 µM (E-)]. SAR analysis though PCA and HCA were performed, suggesting that N-phenylpiperazine is essential to the activity, while increasing volume in the substituted aromatic moiety is detrimental to the potency. This is the first report of the vasodilating properties of such compounds, and studies regarding the mechanism of action are in progress in our group.

Major flavonoids from Psiadia punctulata produce vasodilation via activation of endothelial dependent NO signaling

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Methanol extract of Psiadia punctulata (MAPP) produced a significant vasodilation.

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Chloroform fraction and its methylated flavonoids were responsible for this effect.

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Vasodilation is referred to endothelial nitric oxide and, Ca²⁺ dependent eNOS.

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Interference with calcium entrance is another possible mechanism of vasodilation.

Vasodilators are important pharmacologic agents for managing and/or treating hypertension. Medicinal plants are considered as valuable source of bioactive compounds. We used a bioguided approach to isolate, identify, and investigate the possible vasodilation activities and mechanism(s) of the prepared methanol extract from aerial parts of Psiadia punctulata (MAPP), its bioactive fraction and active compounds. Vascular effects of MAPP were studied using isolated artery technique in the presence or absence of specific candidate pathways inhibitors, and found to produce a significant vasodilation of phenylephrine preconstricted rat aortae. The bioactive chloroform fraction yielded five methoxylated flavonoids: umuhengerin (1), gardenin A (2), gardenin B (3), luteolin-3′,4′ -dimethyl ether (4), and 5,3′-dihydroxy-6,7,4′,5′-tetramethoxyflavone (5). Metabolites 1, 4, and 5 produced a significant vasodilation. Removal of the endothelium significantly inhibited MAPP vasodilation. Nitric oxide synthase inhibition and not prostacycline inhibition or K⁺ channel blocking, was found to cause the observed vasodilation inhibition. Both guanylate cyclase and adenylate cyclase inhibitions markedly inhibited MAPP vasodilation. In conclusion MAPP possesses vasodilation activities that is mediated through endothelial nitric oxide pathway, calcium dependent endothelial nitric oxide synthase activation, and interference with the depolarization process through calcium channel blocking activity.

Beneficial effects of murtilla extract and madecassic acid on insulin sensitivity and endothelial function in a model of diet-induced obesity

Infusions of murtilla leaves exhibit antioxidant, analgesic, and anti-inflammatory properties. Several compounds that are structurally similar to madecassic acid (MA), a component of murtilla leaf extract (ethyl acetate extract, EAE), have been shown to inhibit protein tyrosine phosphatase 1B (PTP1P). The aim of this study was to evaluate if EAE and two compounds identified in EAE (MA and myricetin [MYR]) could have a beneficial effect on systemic and vascular insulin sensitivity and endothelial function in a model of diet-induced obesity. Experiments were performed in 5-week-old male C57BL6J mice fed with a standard (LF) or a very high-fat diet (HF) for 4 weeks and treated with EAE, MA, MYR, or the vehicle as control (C). EAE significantly inhibited PTP1B. EAE and MA, but not MYR, significantly improved systemic insulin sensitivity in HF mice and vascular relaxation to Ach in aorta segments, due to a significant increase of eNOS phosphorylation and enhanced nitric oxide availability. EAE, MA, and MYR also accounted for increased relaxant responses to insulin in HF mice, thus evidencing that the treatments significantly improved aortic insulin sensitivity. This study shows for the first time that EAE and MA could constitute interesting candidates for treating insulin resistance and endothelial dysfunction associated with obesity.

Comparing Medicinal Uses of Cochlospermaceae throughout Its Geographic Range with Insights from Molecular Phylogenetics

Species of the Cochlospermaceae, a small mostly pantropical plant family, were evaluated at a continental scale for medicinal uses in traditional medicine. This ethnobotanical information was placed in a phylogenetic framework to make informed predictions in the search for new medicines and bioactive compounds. Medicinal plant-use data were mapped onto a molecular phylogeny based on DNA sequences of nuclear and chloroplast markers. Associations of medicinal uses among closely related species occurring in different geographic regions and among diverse cultures were evaluated. The most common medicinal uses for these species are those used to treat skin ailments, gastro-intestinal problems, malaria, and liver issues. The plant species with the most numerous uses is Cochlospermum tinctorium, which occurs primarily in West Africa. Closely related species being used by cultural groups in different geographic regions to treat the same illnesses suggests the presence of bioactive compounds with potential biomedical value, since they may represent independent discoveries of similar medicinally-active compounds. This leads to the speculation that those closely related species not currently being used to treat these ailments may also contain identical or similar medicinally-active compounds and are worthy of laboratory investigations.

Pulmonary anti-inflammatory effects and spasmolytic properties of Costa Rican noni juice (Morinda citrifolia L.)

ETHNOPHARMACOLOGICAL RELEVANCE

Morinda citrifolia L. (Noni) is a medicinal plant used in Polynesia for many properties such as anti-inflammatory, anti-diabetic and antineoplastic effects. Recent studies showed that noni juice have anti-oxidant and acute anti-inflammatory activities likely due to polyphenols, iridoids and vitamin C content. The present study was undertaken to evaluate chronic anti-inflammatory and spasmolytic effects of noni juice.

MATERIALS AND METHODS

Therefore, we evaluated the effect of oral or intraperitoneal administrations of noni juice in vivo on the lung inflammation in ovalbumin (OVA) sensitized Brown Norway rat (with prednisolone 10mg/kg intraperitoneously as reference compound) and the ex vivo effect of noni juice on BaCl₂ (calcium signal) or methacholine (cholinergic signal) induced spasms in jejunum segments.

RESULTS

We found that noni juice (intraperitoneously 2.17mL/kg and orally 4.55mL/kg) reduced the inflammation in OVA-sensitized Brown Norway rat with regard to the decreased number of inflammatory cells in lung (macrophages minus 20-26%, lymphocytes minus 58-34%, eosinophils minus 53-30%, neutrophils minus 70-28% respectively). Noni juice demonstrated a dose-dependent NO scavenging effect up to 8.1nmol of nitrites for 50µL of noni juice. In addition noni juice inhibited (up to 90%) calcium and cholinergic induced spasms on the jejunum segments model with a rightward shift of the concentration response curve.

CONCLUSION

We describe for the first time that noni juice demonstrate (1) a chronic anti-inflammatory activity on sensitized lungs along with (2) a spasmolytic effect integrating a calcium channel blocker activity component.

Flavonols in the Prevention of Diabetes-induced Vascular Dysfunction

As flavonols are present in fruits and vegetables, they are consumed in considerable amounts in the diet. There is growing evidence that the well-recognized antioxidant, anti-inflammatory, and vasorelaxant actions of flavonols may, at least in part, result from modulation of biochemical signaling pathways and kinases. It is well established that diabetes is associated with increased cardiovascular morbidity and mortality. Despite clinical management of blood glucose levels, diabetes often results in cardiovascular disease. There is good evidence that endothelial dysfunction contributes significantly to the progression of diabetic cardiovascular diseases. This review describes the biological actions of flavonols that may ameliorate adverse cardiovascular events in diabetes. We discuss evidence that flavonols may be developed as novel pharmacological agents to prevent diabetes-induced vascular dysfunction.

Syzygium cumini (L.) skeels: a prominent source of bioactive molecules against cardiometabolic diseases

Syzygium cumini (Myrtaceae) is a worldwide medicinal plant traditionally used in herbal medicines due to its vaunted properties against cardiometabolic disorders, which include: antihyperglycemic, hypolipemiant, antiinflammatory, cardioprotective, and antioxidant activities. These properties have been attributed to the presence of bioactive compounds such as phenols, flavonoids, and tannins in different parts of the plant, albeit the knowledge on their mechanisms of action is scarce. This mini-review highlights the cardiometabolic properties of S. cumini by correlating its already identified phytochemicals with their described mechanisms of action. Data herein compiled show that some compounds target multiple metabolic pathways; thereby, becoming potential pharmacological tools. Moreover, the lack of clinical trials on S. cumini usage makes it a fruitful field of interest for both scientific community and pharmaceutical industry.

Effects of flavone on the contractile activity of the circular smooth muscle of the rabbit middle colon in vitro

The circular smooth muscles of the middle colon of the rabbit generate giant contractions of high amplitude and low frequency. Flavone, at various concentrations, reduces the giant contractions and the tonic contraction induced by 10 µM carbachol and 80 mM KCl. The contractions induced by dequalinium and tetraethylammonium are reduced by flavone (30 µM). At 100 µM, flavone decreases the contraction induced by 100 µM methylene blue and 1mM orthovanadate. These results suggest that flavone inhibit the giant contractions by (1) inhibition of voltage-dependent Ca(2+) channels, (2) activation of guanyl cyclase, (3) opening of K(+) channels and (4) inhibition of tyrosines kinases.

Spasmogenic effects of Sclerocarya birrea stem bark aqueous extract on rat isolated uterine horns

ETHNOPHARMACOLOGICAL RELEVANCE

Sclerocarya birrea (Anacardiaceae), popularly known as "marula", is used as a traditional remedy for allegedly treating dysmenorrhoea and a host of other ailments such as malaria, fever, diarrhoea, dysentery, stomach disorders, headaches and to facilitate childbirth. This study investigated the pharmacological effects of S. birrea extract (SBE) on isolated, spontaneously-contracting uterine horns of healthy, young adult, female Wistar rats.

MATERIALS AND METHODS

One kilogramme of S. birrea fresh stem bark was identified and authenticated. The bark was air-dried at room temperature (26 ± 1°C) for two weeks. The dried stem bark was milled and macerated in 2.5l of distilled water for 48 h and filtered. A rotary evaporator was used to concentrate the aqueous extract by drying it at 60 ± 1°C. Freeze-drying gave 61.3g/kg (i.e., 6.13% yield) of a dark-brown, powdery, crude extract. Rat isolated uterine horns were mounted in 25-ml Iworx tissue organ-baths containing De Jalon׳s physiological solution, and exposed to graded concentrations of SBE (25, 50, 100, 200, 300, 400mg/ml/kg). The effects of SBE and atropine, oxytocin, verapamil, indomethacin, acetylcholine, serotonin, cimetidine and histamine on the isolated uterine muscles, were recorded using LabScribe2 software.

RESULTS

The aqueous stem bark extract of S. birrea produced significant (p<0.05) concentration-dependent contractions of the uterine horn muscle preparation reaching a maximum at the 300 mg/ml dose. SBE mimicked and potentiated uterine muscle contractile effects of oxytocin (0.5-5 µU/ml) and acetylcholine (0.1-3 µg/ml). Pre-incubation of tissues with atropine (1-3 µg/ml), non-significantly (p>0.05) inhibited SBE-induced contractions on uterine muscles. Verapamil (2 µg/ml), indomethacin and -p-tosyl-l-phenylalanine-chloromethyl-ketone (TPCK) inhibited the contractile effects of SBE (25-400mg/ml/kg), suggesting possible calcium-mediated mechanism of action for SBE and possible COX-enzyme inhibition. Pre-incubating tissues with histamine (10(-8)-10(-5)M) resulted in relaxation of the uterus, while cimetidine potentiated the contractile effects of SBE. Serotonin potentiated the contractile effects of SBE.

CONCLUSION

These results indicate that SBE causes contraction on uterine smooth muscles possibly through its effects on oxytocin, acetylcholine and serotonin receptors. As a result SBE should not be used by patients suffering from dysmenorrhoea as it can worsen it or pregnant patients as it can result in miscarriage/abortion.

The relaxant actions of ethanolic extract of Tridax procumbens (Linn.) on rat corpus cavernosum smooth muscle contraction

BACKGROUND

The effect of Tridax procumbens aqueous ethanolic extract on the rat corpus cavernosum smooth muscles was evaluated in the present study.

METHOD

Corpus cavernosum strips obtained from healthy, young, adult male Wistar albino rats (250-300 g) were precontracted with phenylephrine (10-7 M) or KCl (60 mM) and then treated with various concentrations of T. procumbens extract (0.15-1.05 mg/mL). The change in corpus cavernosum strip tension was recorded. The interactions between T. procumbens extract with acetylcholine and with sodium nitroprusside were also evaluated.

RESULTS

The results indicated that corpus cavernosum strips relaxation induced by T. procumbens extract was concentration-dependent and this was significant (p<0.5). Pre-treatment with a nitric oxide synthase (NOS) inhibitor (N(1) nitro-L-arginine-methyl ester, l-NAME), did not completely inhibit the relaxation. However, T. procumbens extract (0.6 mg/mL) significantly (p<0.5) enhanced both acetylcholine- and sodium nitroprusside-induced corpus cavernosum strips relaxation.

CONCLUSIONS

RESULTS suggest that T. procumbens extract has a concentration-dependent relaxant effect on the isolated rat corpus cavernosum. The mechanism of action of T. procumbens extract is complex. A part of its relaxing effect is mediated directly by the release of NO from endothelium which may improve erectile dysfunction.

Morin Induces Heme Oxygenase-1 via ERK-Nrf2 Signaling Pathway

Background:

Oxidative stress damages to cells or tissues, however, cellular defense systems including heme oxygenase-1 (HO-1) protects them against oxidative stress. Flavonoid compounds can activate cellular defense mechanisms against oxidative stress and it can reduce cell damages. In the present study, the cytoprotective effects of morin (3,5,7,2’,4’-pentahydroxyflavone), in terms of HO-1 enzyme, against the oxidative stress and its involved mechanisms was elucidated.

Methods:

RT-PCR and western blot analysis were assessed to detect the mRNA and protein expression, respectively. Cell viability was measured by using MTT test. The immunocytochemistry was performed to define location of target protein. Electrophoretic mobility shift assay performed to measure transcription factor-promoter site binding activity.

Results:

Morin elevated mRNA and protein levels of HO-1 in human lens epithelial cells (HLE-B3). HO-1 inhibitor ZnPP attenuated the protective effect of morin against H₂O₂-induced cytotoxicity. Morin increased the protein level of transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2), which up-regulates HO-1 expression by binding to the antioxidant response element (ARE) within the HO-1 gene promoter. Moreover, morin induced the translocation of Nrf2 from the cytosol into the nucleus. Morin activated extracellular-regulated kinase (ERK), while ERK inhibitor attenuated morin-enhanced Nrf2 and HO-1 expression.

Conclusions:

Morin activates ERK-Nrf2 signaling cascades in HLE-B3 cells, leading to the up-regulation of HO-1 and cytoprotection against oxidative stress.

Relaxant effect of flavonoid naringenin on contractile activity of rat colonic smooth muscle

ETHNOPHARMACOLOGICAL RELEVANCE

Disturbed gastrointestinal (GI) motility can be associated with smooth muscle abnormalities and dysfunction. Exploring innovative approaches that can modulate the disturbed colonic motility are of great importance for clinical therapeutics. Naringenin, a flavonoid presented in many traditional Chinese herbal medicines, has been shown to have a relaxant effect on different smooth muscles. The aim of the present study was to investigate the effect of naringenin on regulation of GI motility.

MATERIAL AND METHODS

Mechanical recording was used to investigate the effect of naringenin on isolated rat colonic smooth muscle spontaneous contractions. Whole cell patch clamp, intracellular [Ca(2+)] concentration ([Ca(2+)]i) and membrane potential measurements were examined on primary cultures of colonic smooth muscle cells (SMCs). A neostigmine-stimulated rat model was utilized to investigate the effect of naringenin in vivo.

RESULTS

Naringenin induced a concentration-dependent inhibition (1-1000 μM) on rat colonic spontaneous contraction, which was reversible after wash out. The external Ca(2+) influx induced contraction and [Ca(2+)]i increase were inhibited by naringenin (100 μM). In rat colonic SMCs, naringenin-induced membrane potential hyperpolarization was sensitive to TEA and selective large-conductance calcium-activated K(+) (BKCa) channel inhibitor iberiotoxin. Under whole cell patch-clamp condition, naringenin stimulated an iberiotoxin-sensitive BKCa current, which was insensitive to changes in the [Ca(2+)]i concentration. Furthermore, naringenin significantly suppressed neostigmine-enhanced rat colon transit in vivo.

CONCLUSION

Our results for the first time demonstrated the relaxant effect of flavonoid naringenin on colon smooth muscle both in vitro and in vivo. The relaxant effect of naringenin was attributed to direct activation of BKCa channels, which subsequently hyperpolarized the colonic SMCs and decreased Ca(2+) influx through VDCC. Naringenin might be of therapeutic value in the treatment of GI motility disorders.

Relaxation of rat aorta by farrerol correlates with potency to reduce intracellular calcium of VSMCs

Farrerol, isolated from Rhododendron dauricum L., has been proven to be an important multifunctional physiologically active component, but its vasoactive mechanism is not clear. The present study was performed to observe the vasoactive effects of farrerol on rat aorta and to investigate the possible underlying mechanisms. Isolated aortic rings of rat were mounted in an organ bath system and the myogenic effects stimulated by farrerol were studied. Intracellular Ca²⁺ ([Ca²⁺]_in) was measured by molecular probe fluo-4-AM and the activities of L-type voltage-gated Ca²⁺ channels (LVGC) were studied with whole-cell patch clamp in cultured vascular smooth muscle cells (VSMCs). The results showed that farrerol significantly induced dose-dependent relaxation on aortic rings, while this vasorelaxation was not affected by N^G-nitro-l-arginine methylester ester or endothelium denudation. In endothelium-denuded aortas, farrerol also reduced Ca²⁺-induced contraction on the basis of the stable contraction induced by KCl or phenylephrine (PE) in Ca²⁺-free solution. Moreover, after incubation with verapamil, farrerol can induce relaxation in endothelium-denuded aortas precontracted by PE, and this effect can be enhanced by ruthenium red, but not by heparin. With laser scanning confocal microscopy method, the farrerol-induced decline of [Ca²⁺]_in in cultured VSMCs was observed. Furthermore, we found that farrerol could suppress Ca²⁺ influx via LVGC by patch clamp technology. These findings suggested that farrerol can regulate the vascular tension and could be developed as a practicable vasorelaxation drug.

The flavonoid chrysin, an endocrine disrupter, relaxes cholecystokinin- and KCl-induced tension in male guinea pig gallbladder strips through multiple signaling pathways

The bioflavonoids have effects on vascular smooth muscle and gastrointestinal smooth muscle. The flavone and phytoestrogen, chrysin, has been shown to have a vasorelaxant effect on resistance blood vessels. This effect was mediated by nitric oxide (NO). Chrysin inhibited aromatase/estrogen biosynthesis in postmenopausal women. The purpose of this study was to determine if chrysin had an effect on cholecystokinin- or KCl-induced tension in male guinea pig gallbladder strips. In addition, the second messenger(s) system(s) that mediated the effect were to be determined. A pharmacologic approach was used. Male guinea pig gallbladder strips were placed in in vitro chambers filled with Krebs solution, maintained at 37 °C, and gassed with 95% O2-5% CO2. Changes in tension were recorded using a polygraph. It was shown that the PKA/cAMP second messenger system mediated part of the observed chrysin-induced relaxation of cholecystokinin-induced tension, the PKC system also mediated part of the relaxation, and the inhibition of both extracellular Ca(2+) entry and intracellular Ca(2+) release also mediated the chrysin-induced relaxation. This is the first report of chrysin having an effect on gallbladder smooth muscle contraction.

Vasorelaxant effects of the extracts and some flavonoids from the buds of Coreopsis tinctoria

CONTEXT

The buds of Coreopsis tinctoria Nutt (Compositae) are used in the treatment of hypertension in the Uyghur folk medicine in China.

OBJECTIVE

To investigate vasorelaxant properties of extracts and some flavonoids from C. tinctoria (CT) and their underlying mechanisms in isolated rat thoracic aortic rings.

MATERIALS AND METHODS

Vasorelaxant effects of ethanol extracts of CT (CTA) and its flavonoids as well as water-ethanol eluates from CTA by AB-8 resins (CTAA∼CTAF) were evaluated on rat aortic rings pre-contracted with phenylephrine (PE, 1 µM) or high KCl (60 µM). We evaluated the effect of CTA, CTAD and CTAE on PE-induced contraction in a Ca²⁺-free medium and a dose-effect curve of Ca²⁺ in pre-contracted ring with high KCl.

RESULTS

Endothelial removal did not modify the effect of CTAD and CTAE (3.00 g/L) neither on PE-pre-contracted rings (164.78 ± 21.44 and 191.47 ± 16.75%) nor on KCl-pre-contracted rings (75.68 ± 10.76 and 125.14 ± 17.41%) compared with intact-endothelium rings pre-contracted with high KCl (100.49 ± 17.30 and 110.81 ± 16.33%). CTAD and CTAE (3.00 g/L) down-regulated the dose-effect curve of Ca²⁺ in pre-contraction with high KCl, and inhibited the pre-contraction with PE in a Ca²⁺-free medium (p < 0.05). Seven flavonoids were obtained from CTAD, of which luteolin (5) and quercetin (6) were found to be the most effective relaxation in rings precontracted with PE (EC₅₀: 0.006 and 0.039 g/L, p < 0.05) or high KCl (EC₅₀: 0.023 and 0.045 g/L, p < 0.05).

DISCUSSION AND CONCLUSION

These data demonstrated the vasorelaxant effect of CT, and its mechanism is likely due to an inhibitory effect on calcium movements through cell membranes.

Synthesis, docking study and relaxant effect of 2-alkyl and 2-naphthylchromones on rat aorta and guinea-pig trachea through phosphodiesterase inhibition

Chromone (4), which form the base structure of various flavonoids isolated as natural products, is capable of relaxing smooth muscle. This is relevant to the treatment of high blood pressure, asthma and chronic obstructive pulmonary disease. The former disorder involves the contraction of vascular smooth muscle (VSM), and the latter two bronchoconstriction of airway smooth muscle (ASM). One of the principal mechanisms by which flavonoids relax muscle tissue is the inhibition of phosphodiesterases (PDEs), present in both VSM and ASM. Therefore, a study was designed to analyze the structure-activity relationship of chromone derivatives in vaso- and bronchorelaxation through the inhibition of PDE. Docking studies showed that these chromones bind at the catalytic site of PDEs. Consequently, we synthesized analogs of chromones substituted at position C-2 with alkyl and naphthyl groups. These compounds were synthesized from 2-hydroxyacetophenone and acyl chlorides in the presence of DBU and pyridine, modifying the methodology reported for the synthesis of 3-acylchromones by changing the reaction temperature from 80 to 30°C and using methylene chloride as solvent, yielding the corresponding phenolic esters 10a-10h. These compounds were cyclized with an equivalent of DBU, pyridine as solvent, and heated at reflux temperature, yielding the chromones 11a-11h. Evaluation of the vasorelaxant effect of 4, 11a-11h on rat aorta demonstrated that potency decreases with branched alkyl groups. Whereas the EC50 of compound 11d (substituted by an n-hexyl group) was 8.64±0.39 μM, that of 11f (substituted by an isobutyl group) was 14.58±0.64 μM. Contrarily, the effectiveness of the compound is directly proportional to the length of the alkyl chain, as evidenced by the increase in maximal effect of compound 11c versus 11d (66% versus 100%) and 11e versus 11f (60% versus 96%). With an aromatic group like naphthyl as the C-2 substituent, the effectiveness was only 43%. All compounds tested on guinea pig trachea showed less than 55% effectiveness. Compounds 4, 11a-11h were evaluated as PDE inhibitors in vitro, with 11d showing the greatest effect (73%), corroborating the importance of a long alkyl chain, which inhibits the decomposition of cGMP. Docking studies showed that the compound 11d was selective for the inhibition of PDE-5.

Potassium channel openers and prostacyclin play a crucial role in mediating the vasorelaxant activity of Gynura procumbens

Background

Previous studies of Gynura procumbens (G. procumbens) have shown that partially purified fractions of the leaves are capable of lowering the blood pressure of rats by inhibiting angiotensin-converting enzymic activity and causing vasodilatation. The objectives of this study were therefore to further purify the active compounds that exhibited selective effects on blood vessels, determine the mechanism of actions, and to qualitatively analyse the putative compounds present.

Methods

The butanolic fraction (BU) of the crude ethanolic extract was purified using column chromatography to obtain several sub-fractions of different polarities. The in vitro effects of BU and the sub-fractions on vascular tension were subsequently determined using isolated rat thoracic aortic rings. The most potent sub-fraction (F1) alone was then investigated for its mechanisms of the vasorelaxant activity. In another experiment, thin-layer chromatography was used to qualitatively analyse the active compounds found in F1.

Results

The BU and the sub-fractions ranging from 10^-7 to 10^-2 g/ml significantly (p < 0.05) inhibited the sustained tonic contractions induced by phenylephrine and potassium chloride in a concentration-dependent manner with various degree of potency. The most potent sub-fraction (F1) antagonised the calcium-induced vasocontractions (1 x 10^-4 – 1 x 10^-2 M) in calcium-free with high concentration of potassium as well as in calcium- and potassium-free Krebs-Henseleit solutions. Contractions induced by noradrenaline and caffeine were not affected by F1. The vasorelaxing effect caused by F1 was significantly attenuated with preincubation of potassium channel blockers (glibenclamide and 4-aminopyridine) and prostacyclin inhibitor (indomethacin) while it was not affected by preincubation with tetraethylammonium, l-nitro-arginine methyl esther, propanolol, atropine, oxadiazolo quinoxalin one and methylene blue. The qualitative phytochemical analysis of F1 indicated the presence of flavonoids.

Conclusion

These results confirm previous findings that G. procumbens causes vasodilatory effects by blocking calcium channels. In addition, the present study further demonstrates that the vasodilatory effect of G. procumbens may also be due to the opening of potassium channels and the stimulation of prostacyclin production. The putative compounds are probably flavonoids in nature.

Pharmaceutical properties and toxicology of Dioclea grandiflora

CONTEXT

Since the beginning of civilization, herbal medicines have been an important source for human beings to treat their ailments. Despite the large number of synthetic remedies available in the market, the use of plants is seen as a great challenge in the search for new substances endowed with therapeutic properties. One example is Dioclea grandiflora Mart. ex Benth. (Leguminosae) employed in traditional medicine to treat prostate disorders and kidney stones.

OBJECTIVES

This work presents a brief overview of D. grandiflora, including a description of the plant, its chemical composition and pharmacological properties.

METHODS

This review gathers information available in the scientific literature compiled from databases such as Science Direct, PubMed, Dr. Dukes Phytochemical and Ethnobotany, Missouri Botanical Garden and The International Plant Names Index.

RESULTS

The information found in the literature showed that flavonoids are the major constituents of D. grandiflora that account for most of the pharmacological properties so far disclosed. Several studies have revealed that D. grandiflora possesses antinociceptive, cardiovascular, antioxidant and anti-inflammatory activities.

CONCLUSION

Research shows that D. grandiflora is a potential source of compounds pertaining medicinal applications. It provides an interesting subject in the search for new drugs of natural origin.

Diosmin – Isolation Techniques, Determination in Plant Material and Pharmaceutical Formulations, and Clinical Use

Diosmin is a naturally occurring flavone glycoside used in the treatment of venous diseases. In this review, we present the clinical aspects of the use of diosmin preparations in venous stasis, hemorrheologic disorders and vein wall remodeling. Because of its multiple applications in biology and its many therapeutic activities, research on isolation and identification of diosmin is of high relevance. The aim of this review is to present an overview of techniques of isolation and separation of diosmin in plant material, pharmaceutical formulations such as Daflon®, Diosed® and Dioven® tablets, and biological fluids.

Vasorelaxant effects of aqueous leaf extract of Tridax procumbens 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.

Endothelium/nitric oxide mechanism mediates vasorelaxation and counteracts vasoconstriction induced by low concentration of flavanols

PURPOSE

At relatively low concentrations, flavanols induce inconsistent effects on isolated arterial tone, sometimes explained as being due to a structure-activity relationship. The aim of our study was to investigate the effects of two flavanols at different doses on arterial functional state.

METHODS

The effects of two catechins, (-)-epigallocatechin-3-gallate (EGCG) and (-)-epicatechin (EP), on rat-isolated aorta tone were investigated on resting tension and on precontracted preparations, both in the presence and in the absence of endothelium.

RESULTS

At resting tension, endothelium-intact preparations, EGCG and EP (0.01-10 μM), induced a slight concentration-dependent, non-significant contraction. On endothelium-denuded preparations, both EGCG and EP induced a concentration-dependent contraction (significance at 0.1 and 1 μM concentrations of the two compounds, respectively). In phenylephrine (PE) (1 μM) precontracted, endothelium-intact preparations, EGCG and EP (0.01-10 μM), induced a concentration-dependent vasorelaxation, reaching significance at 1 μM concentration of both agonists. On endothelium-denuded preparations, EGCG and EP did not significantly affect PE (0.3 μM)-induced tone. In endothelium-intact precontracted preparations, Nω nitro-L-arginine (L-NNA), a nitric oxide synthase (NOS) activity inhibitor, abolished the vasorelaxant effect of EGCG and EP (0.01-10 μM). At high concentrations, EGCG and EP (100 μM) elicited a marked relaxation. This was significantly larger in the presence than in the absence of endothelium or in the presence of L-NNA.

CONCLUSIONS

Our findings highlight the important role played by an endothelium/NO-mechanism in the regulation of basal tone and in both mediating vasorelaxation and counteracting vasoconstriction induced by low concentrations of flavanols in rat thoracic aorta.

Gnaphaliin A and B relax smooth muscle of guinea-pig trachea and rat aorta via phosphodiesterase inhibition

OBJECTIVES

To explore the relaxant mechanism of action of gnaphaliin A and gnaphaliin B in guinea-pig trachea and rat aorta, and to investigate the theoretical and experimental phosphodiesterase (PDE) inhibitory activity of these flavones.

METHODS

The relaxant effect and the inhibition of calcium chloride induced contractions of both flavones were evaluated on guinea-pig trachea and rat aorta rings. The PDE inhibitory activity was evaluated using a cyclic nucleotide PDE colorimetric assay kit with cAMP and cGMP as substrates. The docking analysis was carried out with AutoDock4 software and X-ray structure of PDE type 5. The activity of both gnaphaliins was compared with the activity of sildenafil, rolipram, aminophylline, IBMX and enoximone.

KEY FINDINGS

Gnaphaliin A and B were more actives as relaxants on rat aorta than guinea-pig trachea. They were less potent in the relaxation of guinea-pig trachea and rat aorta than sildenafil, but they were equal or more potent than the other PDE inhibitors tested. The relaxant effect of these flavones was potentiated by nitroprusside and forskolin, and blocked by 1H-[1,2,4]-oxadiazolo[4,3-a]quinoxalin-1-one but not by 2',5'-dideoxyadenosine in guinea-pig trachea. L-NAME did not modify the relaxant effect of gnaphaliins. Gnaphaliins were more potent as PDE inhibitors when cGMP was used as substrate. Docking analysis revealed that gnaphaiins bind to the same binding site of sildenafil at PDE type 5.

CONCLUSIONS

The results suggest that the main relaxant mechanism of action of gnaphaliin A and B is inhibition of PDEs with a preference to inhibit the degradation of cGMP. The docking study suggested that these flavones bind with high specificity to the same binding site of sildenafil at PDE type 5.

Possible mechanisms of vasorelaxation for 5,7-dimethoxyflavone from Kaempferia parviflora in the rat aorta

The present study investigated the vascular effects of 5,7-dimethoxyflavone (DMF), isolated from the rhizomes of Kaempferia parviflora (KP), on rat isolated aortic rings and its possible mechanisms. DMF (1-100 μM) caused concentration-dependent relaxations in aortic rings precontracted with methoxamine. This effect was significantly reduced by removal of the endothelium, and after pretreatment with N(G)-nitro-L-arginine methyl ester (L-NAME, 300 μM), indomethacin (10 μM) and 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ, 10 μM), but not 9-(tetrahydro-2-furanyl)-9H-purine-6-amine (SQ22536, 100 μM). Relaxant responses to DMF were significantly inhibited by high KCl (60 mM) in both endothelium-intact and -denuded rings. In addition, the relaxations to DMF were significantly reduced by pretreatment with tetraethylammonium (TEA, 5 mM), glibenclamide (10 μM), 4-aminopyridine (1 mM) or barium chloride (10 μM). Preincubation with DMF (10 and 100 μM) for 30 min significantly inhibited the contractile responses to CaCl(2) in a Ca(2+)-free, high K(+) buffer. The present study demonstrated that DMF causes endothelium-dependent relaxation that is partly mediated by NO-cGMP and cyclooxygenase pathways. Interestingly, DMF-induced responses are mainly due to increasing K(+) efflux, and inhibition of Ca(2+) influx from the extracellular space. The vasodilator effects of DMF provide experimental support for the potential use of KP as a medical plant in the treatment of cardiovascular diseases.

Effects of resveratrol and flavonols on cardiovascular function: Physiological mechanisms

Resveratrol and flavonols are commonly found together in fruits and vegetables and, therefore, consumed in the diet. These two polyphenols share both vasorelaxant and antioxidant activity and may act together to improve cardiovascular function. This review examines the mechanisms by which resveratrol and flavonols influence cardiovascular function and perhaps offer a new approach for the development of therapeutic agents for the prevention and/or treatment of coronary artery disease.

Cochlospermum vitifolium induces vasorelaxant and antihypertensive effects mainly by activation of NO/cGMP signaling pathway

AIM OF THE STUDY

Cochlospermum vitifolium is a medicinal plant used for the treatment of diabetes, hepatobilary and cardiovascular illnesses. The aim of current study was to determine the in vivo antihypertensive and in vitro functional vasorelaxant mechanism of methanol extract of Cochlospermum vitifolium (MECv) and naringenin (NG).

MATERIALS AND METHODS

Test material was assayed on rat isolated aorta rings test with- and without-endothelium to determine their vasorelaxant mechanism. Also, the in vivo antihypertensive effect was evaluated on spontaneously hypertensive rat (SHR) model. In addition, presence of NG into the extract was confirmed by reverse phase high performance liquid chromatography (RP-HPLC) analysis.

RESULTS

MECv (120 mg/kg) and NG (50 and 160 mg/kg) showed acute antihypertensive effects on SHR when systolic and diastolic pressure were decreased at 1 h and 24 h after administration, respectively. Vasorelaxant effect of MECv and NG was shifted to the right when endothelium-intact aortic rings were pre-incubated with L-NAME (10 microM) and ODQ (1 microM). Also, NG relaxant curves were displaced to the right in the presence of tetraethylammonium (TEA, 1 mM) and 2-aminopyridine (2-AP, 100 microM) on endothelium-denuded aortic rings.

CONCLUSION

Experiments described above showed that MECv play an important role in hypertension regulation through NO synthesis and may be PGI(2) production and potassium channel activation on excessive endothelial dysfunction conditions. Unfortunately, presence of NG into the extract is not significant on bioactivity of the extract; however, this compound could be tested and evaluated as structural scaffold for future drug design for development of antihypertensive agents.

Flavonoid galangin prevents smooth muscle fatigue of pig urinary bladder

There is increasing evidence that the generation of free radicals plays a role in the development of bladder dysfunction. Flavonoids are a group of polyphenolic compounds with broad pharmacological activity. In the present study, the protective effects of the flavonoid galangin on the progressive decrease of bladder smooth muscle contractile responses during repetitive field stimulation (RFS; a model for muscular fatigue) were demonstrated. Pig detrusor strips were mounted for tension recording in organ baths and were subjected to RFS for 90 min at 32 Hz for 15 s every 5 min. The strips were then washed four times with fresh buffer and allowed a period of recovery for 90 min. The 90 min of RFS caused a progressive decrease in maximal contractile response to electrical field stimulation and to muscarinic agonist-induced contractions (34% and 46% decrease, respectively). Galangin (10−7m) prevented the decrease in contractile smooth muscle response of strips to electrical field stimulation during RFS compared with untreated tissues. The antioxidant activity of galangin was assessed by measuring its ability to inhibit the lipid peroxidation induced by iron and ascorbate in rat liver microsomes (IC50 1.7 + 0.12 times 10−6m). If the data are confirmed in-vivo, exogenously administered galangin may be a new approach in the prevention and/or treatment of bladder dysfunction.

Cardiovascular protective flavonolignans and flavonoids from Calamus quiquesetinervius

Tricin-type flavonolignans, (2S)-dihydrotricin 4'-O-(erythro-beta-guaiacylglyceryl) ether, (2S)-dihydrotricin 4'-O-(threo-beta-guaiacylglyceryl) ether, (2S)-dihydrotricin 4'-O-(threo-beta-4-hydroxyphenylglyceryl) ether, tricin 4'-O-(erythro-beta-4-hydroxyphenylglyceryl) ether, tricin 4'-O-(threo-beta-4-hydroxylphenylglyceryl) ether, and (2S)-dihydrotricin 4'-O-(beta-6''-methoxy-4''-oxo-chroman-3''-yloxy) ether namely calquiquelignan A-F, respectively, were isolated and characterized from the EtOAc extract of Calamus quiquesetinervius. Additionally, six known phenolic compounds, including dihydrotricin, tricin, salcolin A, p-hydroxybenzoic acid, (2S, 3S)-trans-dihydrokapempferol and (2S)-naringenin, were also obtained and identified from the extract. Structures of the flavonolignans were assigned based on spectroscopic analyses that included 1D and 2D NMR spectroscopic techniques, such as HMQC, HMBC, and NOESY. Bioassay results showed that calquiquelignan A, dihydrotricin and (2S)-naringenin exhibited significant vasodilatory potencies, as indicated by 60.3%, 80.3% and 60.9% relaxations, respectively, at 100 microM. Salcolin A showed potent platelet aggregation inhibition, compared with aspirin. Most of the tricin-type derivatives (calquiquelignan A-B, dihydrotricin and tricin) also exhibited more potent hydroxyl radical ((.)OH) scavenging activity than trolox as characterized by the ultraweak chemiluminescence assay.

The flavonoid dioclein is a selective inhibitor of cyclic nucleotide phosphodiesterase type 1 (PDE1) and a cGMP-dependent protein kinase (PKG) vasorelaxant in human vascular tissue

The inhibitory effect of the flavonoid dioclein was assessed on purified vascular cyclic nucleotide phosphodiesterase isoforms (EC 3.1.4.17, PDE1-5) in comparison with 8-methoxymethyl-isobutylmethylxanthine (8-MM-IBMX) and vinpocetine which are currently used as PDE1 inhibitors. The mechanism underlying the vasorelaxant effect of dioclein was investigated in human saphenous vein. Dioclein inhibited PDE1 more selectively than vinpocetine and 8-MM-IBMX, with IC(50) values of 2.47+/-0.26 and 1.44+/-0.35 microM, respectively in basal- and calmodulin-activated states. Dioclein behaved as a competitive inhibitor for cGMP hydrolysis by PDE1 in basal- and calmodulin-activated states (K(i)=0.62+/-0.14 and 0.55+/-0.07 microM, respectively), indicating this inhibitory effect to be independent of calmodulin interactions. In addition, dioclein induced a concentration-dependent relaxation of human saphenous vein which was independent on the presence of functional endothelium (EC(50) values of 7.3+/-3.1 and 11+/-2.7 microM, respectively with and without endothelium). 8-MM-IBMX relaxed human saphenous vein with an EC(50)=31+/-16 microM, whereas vinpocetine did not cause any vasorelaxation at concentrations up to 100 microM. Rp-8-pCPT-cGMPS, which inhibits cGMP-dependent protein kinase (PKG), blocked the vasodilator effect of dioclein, whereas H-89, which is a cAMP-dependent protein kinase (PKA) inhibitor, had a minor inhibitory effect. Our data show that dioclein is a potent calmodulin-independent selective inhibitor of PDE1 and that inhibition of PDE1 is involved in the PKG-mediated vasorelaxant effect of dioclein in human saphenous vein. Furthermore, dioclein may represent a new archetype to develop more specific PDE1 inhibitors.

Flavone Attenuates Vascular Contractions by Inhibiting RhoA/Rho Kinase Pathway

Our previous study demonstrated that flavone inhibits vascular contractions by decreasing the phosphorylation levelof the myosin phosphatase target subunit (MYPT1). In the present study, we hypothesized that flavone attenuates vascular contractions through the inhibition of the RhoA/Rho kinase pathway. Rat aortic rings were denuded of endothelium, mounted in organ baths, and contracted with either 30 nM U46619 (a thromboxane A2 analogue) or 8.0 mM NaF 30 min after pretreatment with either flavone (100 or 300 microM) or vehicle. We determined the phosphorylation level of the myosin light chain (MLC(20)), the myosin phophatase targeting subunit 1 (MYPT1) and the protein kinase C-potentiated inhibitory protein for heterotrimeric myosin light chain phophatase of 17-kDa (CPI17) by means of Western blot analysis. Flavone inhibited, not only vascular contractions induced by these contractors, but also the levels of MLC(20) phosphorylation. Furthermore, flavone inhibited the activation of RhoA which had been induced by either U46619 or NaF. Incubation with flavone attenuated U46619-or NaF-induced phosphorylation of MYPT1(Thr855) and CPI17(Thr38), the downstream effectors of Rho-kinase. In regards to the Ca(2+)-free solution, flavone inhibited the phosphorylation of MYPT1(Thr855) and CPI17(Thr38), as well as vascular contractions induced by U46619. These results indicate that flavone attenuates vascular contractions, at least in part, through the inhibition of the RhoA/Rho-kinase pathway.

Vascular reactivity is affected by dietary consumption of wild blueberries in the Sprague-Dawley rat

We have previously reported that consumption of blueberry-enriched (BB) diets attenuates the arterial contractile response to alpha(1)-adrenergic stimuli and affects vasomotor tone via endothelium-related pathways. The present study was designed to evaluate vascular function and responsiveness in aortas of weanling male Sprague-Dawley rats fed a control (C) or a BB diet for 7 weeks. Vascular ring studies were conducted in 3-mm isolated rat aortic ring preparations to investigate vasoconstriction induced by L-phenylephrine (Phe) (10(-8)-3 x 10(-6) M) and vasorelaxation induced by acetylcholine (ACh) (10(-8)-3 x 10(-6) M). Agonists were used alone and in the presence of nitric oxide (NO) synthase and cyclooxygenase (COX) inhibitors. We observed a significantly diminished vasoconstrictor response to Phe in aortic rings from rats fed the BB diet. Inhibition of NO synthase but not COX caused a significant increase in the constrictor response in both dietary groups, with the BB group having the greater response. Similarly, the participation of the NO pathway in endothelium-dependent vasorelaxation induced by ACh was greater in the rats fed a BB diet, while COX inhibition showed no effect on maximum ACh-induced vasorelaxation in any diet group. The vessel sensitivity of BB aortic rings to the vasoconstrictor and vasodilator was significantly reduced when compared to controls. We have concluded that diets enriched with blueberries, fed for 7 weeks in Sprague-Dawley rats, seem to affect NO metabolic pathways in the aorta at basal and stimulated levels.

Gastric relaxation induced by apigenin and quercetin: analysis of the mechanism of action

AIMS

Recently, flavonoids have been shown to cause murine gastric relaxation. In the present study we examined the mechanism of action underlying gastric relaxation induced by apigenin and quercetin in isolated mouse stomach.

MAIN METHODS

The mechanical activity from the whole stomach was detected as changes in the endoluminal pressure and the response to increasing concentrations of both flavonoids were tested before and after different pharmacological treatments.

KEY FINDINGS

Apigenin and quercetin-induced a concentration-dependent gastric relaxation, apigenin being more potent than quercetin. The responses were unaffected by 2'5'dideoxyadenosine, an inhibitor of adenylate cyclase, 3-isobutyl-1-methylxanthine, a non selective inhibitor of cyclic nucleotide phosphodiesterase, or ryanodine, an inhibitor of calcium release from ryanodine-sensitive intracellular stores, whereas they were significantly decreased in Ca(2+)-free solution or in the presence of nifedipine, a blocker of L-type voltage-dependent Ca(2+) channels, which did not modify the relaxation induced by isoproterenol. Moreover, both flavonoids caused concentration-dependent inhibition of the contractile responses caused by exogenous application of Ca(2+) in a Ca(2+)-free solution, high K(+) or carbachol.

SIGNIFICANCE

Our results support the hypothesis that the gastric myorelaxant effects of apigenin and quercetin arise from their negative modulation of calcium influx through voltage-dependent Ca(2+) channels, however intracellular modulation of signalling cascade leading to contraction could be involved.

Biphasic effect of Psidium guajava Linn. (Myrtaceae) leaf aqueous extract on rat isolated vascular smooth muscles

In this study, we examined the effects of Psidium guajava Linn. leaf aqueous extract (PGE) on isolated, spontaneously-contracting portal veins, as well as on endothelium-intact and endothelium-denuded descending thoracic aortic ring preparations of healthy, normotensive rats. Graded concentrations of PGE (0.25-4.0 mg/ml) caused concentration-dependent, initial brief but significant (P<0.05) rises of the basal tones and amplitudes of pendular, rhythmic contractions, followed by secondary pronounced, longer-lasting and significant (P<0.05-0.001) inhibitions of contractile amplitudes of the isolated portal veins. Relatively low concentrations of PGE (<1.0 mg/ml) always contracted freshly-mounted, naïve, endothelium-intact aortic ring preparations. However, relatively high concentrations of PGE (1.0-4.0 mg/ml) always produced initial brief contractions/augmentations of noradrenaline (NA, 10(-7)M)-induced contractions of endothelium-intact and endothelium-denuded aortic ring preparations, followed by secondary, pronounced relaxations of the aortic ring muscles. Moreover, relatively high concentrations of PGE (1.0-4.0 mg/kg) always relaxed NA-induced contractions of the aortic ring preparations in a concentration-related manner. The arterial-relaxing effects of PGE were more pronounced in endothelium-intact aortic rings than in endothelium-denuded aortic ring preparations. The relaxant effects of PGE on endothelium-intact aortic rings were only partially inhibited by N(G)-nitro-L-arginine methyl ester (L-NAME, 100 microM), a nitric oxide synthase inhibitor, suggesting that the vasorelaxant effect of PGE on aortic rings is probably mediated via both endothelium-derived relaxing factor (EDRF)-dependent and EDRF-independent mechanisms. Taken together, the findings of this study indicate that PGE possesses a biphasic effect on rat isolated vascular smooth muscles.

Pharmacological studies on hypotensive, diuretic and vasodilator activities of chrysin glucoside from Calycotome villosa in rats

The present study was undertaken in normotensive anaesthetized male rats that received a continuous perfusion of a chrysin glucoside isolated from the flowers and leaves of Calycotome villosa subsp intermedia at a dose of 2.5 mg/kg, or furosemide (control diuretic) at a dose of 0.5 mg/kg. Compared with the control rats receiving NaCl (0.9%), the urine flow, glomerular filtration and electrolyte excretion (Na+, K+) increased significantly in rats treated with chrysin glucoside (p < 0.001). A similar effect was observed in the rats perfused with furosemide. Intravenous injections of bolus doses (1-3 mg/kg) of the chrysin glucoside to anaesthetized rats elicited an immediate and dose-dependent decrease in mean arterial blood pressure (MABP). Pretreatment of the rats with the nitric oxide synthase inhibitor, l-NOArg (10 mg/kg), reduced partially, but significantly (p < 0.01), the maximal decrease in MABP elicited by chrysin glucoside. In the rat isolated aorta preparation, chrysin glucoside (10-100 microm) inhibited in a concentration-dependent manner the noradrenaline (1 microm) induced contractions (IC(50) = 52 microm). This relaxant activity of chrysin glucoside was significantly reduced by incubation of the endothelium-intact rings with l-NOArg (100 microm), (80 +/- 4.7% vs 48 +/- 5.06% in the absence of L-NOArg). In conclusion, these results demonstrate a diuretic and hypotensive action of a chrysin glucoside from Calycotome villosa in anaesthetized rats and indicating an action on renal function, and an active vascular relaxation mediated partially through nitric oxide release.

Relaxant effects of flavonoids on the mouse isolated stomach: structure-activity relationships

Flavonoids are a large heterogeneous group of benzo-gamma-pyrone derivatives, which are abundantly present in our diet. In this study we investigated the effects of six flavonoids (apigenin, genistein, quercetin, rutin, naringenin and catechin) on the gastric tone in mouse isolated stomach. The mechanical activity was recorded as changes of intraluminal pressure. All flavonoids tested produced a concentration-dependent relaxation, which was reversible after washout. The relative order of potency of the flavonoids was apigenin> or =genistein>quercetin>naringenin> or =rutin>catechin. Analysis of the chemical structure showed that the relaxant activity was progressively diminished by the presence of hydroxyl group at C-3, saturation of the C-2, C-3 double bound, saturation of the C-2, C-3 double bound coupled with lack of the C-4 carbonyl and glycosylation. The flavonoid-induced relaxations were not modified in the presence of tetrodotoxin, a voltage-dependent Na(+)-channel blocker, N(omega)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase, indomethacin, an inhibitor of cycloxygenase or tetraethylammonium, a non-selective blocker of potassium channels. In conclusion, this study provides the first experimental evidence for gastric relaxant activity of flavonoids. This action is influenced to a great extent by the structure of the molecules and it seems not to be dependent on neural action potentials, NO/prostaglandin production or activation of K(+) channels.

Flavone inhibits vascular contraction by decreasing phosphorylation of the myosin phosphatase target subunit

1. Flavonoids modulate vascular tone through an endothelium-dependent or -independent mechanism. Although a few mechanisms for endothelium-independent relaxation have been suggested, such as interference with protein kinase C or cAMP or cGMP phosphodiesterase, the inhibition of Ca(2+) release from intracellular stores or Ca(2+) influx from extracellular fluids, the mode of action of flavonoids remains elusive. 2. We hypothesized that treatment with flavone inhibits vascular smooth muscle contraction by decreasing the phosphorylation of the myosin phosphatase target subunit (MYPT1). 3. Rat aortic rings were denuded of endothelium, mounted in organ baths and contracted with U46619, a thromboxane A(2) analogue. 4. Flavone dose-dependently inhibited the U46619-induced contractile response and myosin light chain (MLC(20)) phosphorylation. At 10(-7) mol/L, U46619 induced vascular contraction with the concomitant phosphorylation of MYPT1 at Thr855, but not at Thr697. Incubation with flavone (100 or 300 micromol/L) for 30 min attenuated the phosphorylation of MYPT1(Thr855), but not MYPT1(Thr697). 5. It is concluded that treatment with flavone inhibits vascular smooth muscle contraction by decreasing the phosphorylation of the MYPT1. These results suggest that flavone causes endothelium-independent relaxation through, at least in part, the inhibition of p160 Rho-associated coiled-coil-containing protein kinase (ROCK) signalling.

Study of the mechanisms involved in the vasorelaxation induced by (-)-epigallocatechin-3-gallate in rat aorta

This study investigated several mechanisms involved in the vasorelaxant effects of (-)-epigallocatechin-3-gallate (EGCG). EGCG (1 microM-1 mM) concentration dependently relaxed, after a transient increase in tension, contractions induced by noradrenaline (NA, 1 microM), high extracellular KCl (60 mM), or phorbol 12-myristate 13-acetate (PMA, 1 microM) in intact rat aortic rings. In a Ca2+ -free solution, EGCG (1 microM-1 mM) relaxed 1 microM PMA-induced contractions, without previous transient contraction. However, EGCG (1 microM-1 mM) did not affect the 1 microM okadaic acid-induced contractions. Removal of endothelium and/or pretreatment with glibenclamide (10 microM), tetraethylammonium (2 mM) or charybdotoxin (100 nM) plus apamin (500 nM) did not modify the vasorelaxant effects of EGCG. In addition, EGCG noncompetitively antagonized the contractions induced by NA (in 1.5 mM Ca2+ -containing solution) and Ca2+ (in depolarizing Ca2+ -free high KCl 60 mM solution). In rat aortic smooth muscle cells (RASMC), EGCG (100 microM) reduced increases in cytosolic free Ca2+ concentration ([Ca2+]i) induced by angiotensin II (ANG II, 100 nM) and KCl (60 mM) in 1.5 mM CaCl2 -containing solution and by ANG II (100 nM) in the absence of extracellular Ca2+. In RASMC, EGCG (100 microM) did not modify basal generation of cAMP or cGMP, but significantly reversed the inhibitory effects of NA (1 microM) and high KCl (60 mM) on cAMP and cGMP production. EGCG inhibited the enzymatic activity of all the cyclic nucleotide PDE isoenzymes present in vascular tissue, being more effective on PDE2 (IC50 approximately 17) and on PDE1 (IC50 approximately 25). Our results suggest that the vasorelaxant effects of EGCG in rat aorta are mediated, at least in part, by an inhibition of PDE activity, and the subsequent increase in cyclic nucleotide levels in RASMC, which, in turn, can reduce agonist- or high KCl concentration-induced increases in [Ca2+]i.