Inhibitory effects of quercetin and staurosporine on phasic contractions in rat vascular smooth muscle

Anti-Asthmatic Effects of Portulaca Oleracea and its Constituents, a Review

OBJECTIVES

The medicinal plants are believed to enhance the natural resistance of the body to infections. Some of the main constituents of the plant and derived materials such as, proteins, lectins and polysaccharides have anti-inflammatory effects. Portulaca oleracea (P. oleracea) were used traditionally for dietary, food additive, spice and various medicinal purposes. This review article is focus on the anti-asthmatic effects of P. oleracea and its constituents.

METHODS

Various databases, such as the PubMed, Scopus, and Google Scholar, were searched the keywords including "Portulaca oleracea", "Quercetin", "Anti-inflammatory", "Antioxidant", "Cytokines", "Smooth muscle ", and " Relaxant effects " until the end of Jul 2018.

RESULTS

P. oleracea extracts and its constituents increased IFN-γ, IL-2, IFNγ/IL-4 and IL- 10/IL-4 ratio, but decreased secretion of TNF-α, IL-4 and chemokines in both in vitro and in vivo studies. P. oleracea extracts and quercetin also significantly decreased production of NO, stimulated β-adrenoceptor and/or blocking muscarinic receptors in tracheal smooth muscles. Conclusion: P. oleracea extracts and quercetin showed relatively potent anti-asthmatic effects due to decreased production of NO, inflammatory cytokines and chemokines, reduced oxidant while enhanced antioxidant markers, and also showed potent relaxant effects on tracheal smooth muscles via stimulatory on β-adrenoceptor or/and blocking muscarinic receptors.

Different mechanisms of actions of genistein, quercetin on spontaneous contractions of rabbit duodenum

Flavonoids are known to relax precontracted intestinal smooth muscle and delay intestinal transit or intestinal peristalsis. The aim of this study was to determine the effects of genistein and quercetin on spontaneous contractions of rabbit duodenum in vitro in an organ bath. Genistein and quercetin (0.1-10µM) reduced the amplitude of spontaneous contractions in the longitudinal and circular smooth muscle of rabbit duodenum, but they did not modify the frequency. Bay K8644 (L-type Ca2+ channel activator), apamin, charybdotoxin, and tetraetylammonium (K+ channel blockers) reverted the inhibition of amplitude of spontaneous contractions induced by genistein in longitudinal and circular smooth muscle. H-89 (protein kinase A inhibitor) antagonized the reduction of the amplitude of spontaneous contractions induced by quercetin in longitudinal and circular smooth muscle of duodenum, while 2,5-dideoxiadenosine (adenylyl cyclase inhibitor) reverted only the reduction of the amplitude in circular smooth muscle. In conclusion, genistein and quercetin reduce the spontaneous contractions in the duodenum by different mechanisms of actions. The effect of genistein would be mediated by Ca2+ and K+ channels, while the effect of quercetin would be mediated by cAMP and protein kinase A.

The effects of Ginseng Java root extract on uterine contractility in nonpregnant rats

Ginseng Java or Talinum paniculatum (Jacq.) Geartn has long been used in herbal recipes because of its various therapeutic properties. Ginseng Java is believed to be beneficial to the female reproductive system by inducing lactation and restoring uterine functions after the postpartum period. There are, however, no scientific data on verifying the effects on the uterus to support its therapeutic relevance. Therefore, the purpose of this study was to investigate the effects of Ginseng Java root extract and its possible mechanism(s) of action on uterine contractility. Female virgin rats were humanely killed by CO₂ asphyxia and uteri removed. Isometric force was measured in strips of longitudinal myometrium. The effects of Ginseng Java root extract at its IC₅₀ concentration (0.23 mg/mL) on spontaneous, oxytocin‐induced (10 nmol/L), and depolarized (KCl 40 mmol/L) contraction were investigated. After establishing regular phasic contractions, the application of Java root extract significantly inhibited spontaneous uterine contractility (n =5). The extract also significantly inhibited the contraction induced by high KCl solution (n =5) and oxytocin (n =5). The extract also inhibited oxytocin‐induced contraction in the absence of external Ca entry (n =7) and the tonic force induced by oxytocin in the presence of high KCl solution. Taken together, the data demonstrate a potent and consistent ability of extract from Ginseng Java root to reduce myometrial contractility. The tocolytic effects were demonstrated on both spontaneous and agonist‐induced contractions. The fact that force was inhibited in depolarized conditions suggests that the possible mechanisms may be blockade of Ca influx via L‐type Ca channels. The data in Ca‐free solutions suggest that the extract also reduces IP₃‐induced Ca release from the internal store. These tocolytic effects do not support the use of ginseng to help with postpartum contractility, but instead suggest it may be helpful in reducing inappropriate uterine contractions, such as in threatened preterm delivery.

The data demonstrate a potent and consistent ability of extract from Ginseng Java root to reduce myometrial contractility. The tocolytic effects were demonstrated on both spontaneous and agonist‐induced contractions.

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.

Glucuronidated quercetin lowers blood pressure in spontaneously hypertensive rats via deconjugation

Background

Chronic oral quercetin reduces blood pressure and restores endothelial dysfunction in hypertensive animals. However, quercetin (aglycone) is usually not present in plasma, because it is rapidly metabolized into conjugated, mostly inactive, metabolites. The aim of the study is to analyze whether deconjugation of these metabolites is involved in the blood pressure lowering effect of quercetin.

Methodology/Principal Findings

We have analyzed the effects on blood pressure and vascular function in vitro of the conjugated metabolites of quercetin (quercetin-3-glucuronide, Q3GA; isorhamnetin-3-glucuronide, I3GA; and quercetin-3′-sulfate, Q3'S) in spontaneously hypertensive rats (SHR). Q3GA and I3GA (1 mg/kg i.v.), but not Q3'S, progressively reduced mean blood pressure (MBP), measured in conscious SHR. The hypotensive effect of Q3GA was abolished in SHR treated with the specific inhibitor of β-glucuronidase, saccharic acid 1,4-lactone (SAL, 10 mg/ml). In mesenteric arteries, unlike quercetin, Q3GA had no inhibitory effect in the contractile response to phenylephrine after 30 min of incubation. However, after 1 hour of incubation Q3GA strongly reduced this contractile response and this effect was prevented by SAL. Oral administration of quercetin (10 mg/Kg) induced a progressive decrease in MBP, which was also suppressed by SAL.

Conclusions

Conjugated metabolites are involved in the in vivo antihypertensive effect of quercetin, acting as molecules for the plasmatic transport of quercetin to the target tissues. Quercetin released from its glucuronidated metabolites could be responsible for its vasorelaxant and hypotensive effect.

Chrysosplenol C increases contraction in rat ventricular myocytes

Chrysosplenol C (4',5,6-trihydroxy-3,3',7-trimethoxyflavone) is a flavone contained in several medicinal plants including Miliusa balansae and Pterocaulon sphacelatum. This compound is known to have an antiviral effect and show cytotoxic activity in several cell lines. In the present study, we explored the effect of chrysosplenol C on contractility in isolated adult rat ventricular myocytes. Chrysosplenol C was isolated from M. balansae, and cell shortenings were measured in field-stimulated single myocytes using a video edge detection method at room temperature. Chrysosplenol C was found to increase cell shortenings in a dose-dependent manner with a half-maximal effective concentration of 45 ± 7.8 μM. Maximal effect of chrysosplenol C, approximately 185% of control, was observed at ≥80 μM. The positive inotropic effect caused by chrysosplenol C was reversible. Time-to-peak contraction and time-to-relengthening were significantly increased by chrysosplenol C. The velocity of cell shortening was slightly accelerated, whereas that of relaxation was not altered by chrysosplenol C. The chrysosplenol C–induced positive inotropic effect was not inhibited by propranolol posttreatment or H-89 pretreatment, suggesting that chrysosplenol C increased contraction independently of β-adrenergic receptor stimulation and protein kinase A. Our findings are the first to demonstrate that chrysosplenol C is a positive inotropic agent in cardiac myocytes.

The effects of a multiflavonoid supplement on vascular and hemodynamic parameters following acute exercise

Antioxidants can decrease oxidative stress and combined with acute exercise they may lead to further decreases in blood pressure. The purpose of this study was to investigate the effects of 2 weeks of antioxidant supplementation on vascular distensibility and cardiovascular hemodynamics during postexercise hypotension. Methods. Twenty young subjects were randomized to placebo (n = 10) or antioxidant supplementation (n = 10) for two weeks. Antioxidant status, vascular distensibility, and hemodynamics were obtained before, immediately, and 30 minutes after an acute bout of aerobic exercise both before and after supplementation. Results. Two weeks of antioxidant supplementation resulted in a greater systolic blood pressure (SBP) decrease during postexercise hypotension (PEH) and significant decreases in augmentation index versus placebo (12.5% versus 3.5%, resp.). Also ferric-reducing ability of plasma (FRAP) increased significantly (interaction P = 0.024) after supplementation. Conclusion. Supplementation showed an additive effect on PEH associated with increased FRAP values and decreases in systolic blood pressure and augmentation index.

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.

Endothelium-independent vasodilator effects of the flavonoid quercetin and its methylated metabolites in rat conductance and resistance arteries

The flavonoid quercetin is metabolized into isorhamnetin, tamarixetin, and kaempferol, the vascular effects of which are unknown. In the present study, the effects of quercetin and its metabolites were analyzed on isometric tension in isolated rat thoracic and abdominal aorta, in isolated intact and beta-escin-permeabilized iliac arteries, and on perfusion pressure in the isolated mesenteric resistance vascular bed. In noradrenaline-precontracted vessels, the four flavonoids produced a vasodilator effect, which was inversely correlated with the diameter of the vessel studied; i.e., quercetin, isorhamnetin, tamarixetin, and kaempferol were 5-, 25-, 4-, and 6-fold, respectively, more potent in the resistance mesenteric bed (-log IC(50) = 5.35 +/- 0.15, 5.89 +/- 0.11, 5.34 +/- 0.10, and 5.66 +/- 0.06, respectively) than in the thoracic aorta (-log IC(50) = 4.68 +/- 0.08, 4.61 +/- 0.08, 4.73 +/- 0.11, and 4.81 +/- 0.13, respectively; n = 4-6). The vasodilator responses of quercetin and isorhamnetin were not significantly modified after removal of the endothelium in the thoracic aorta or in the mesenteric bed. Furthermore, the guanylate cyclase inhibitor ODQ (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one; 10(-6) M), the adenylate cyclase inhibitor SQ22536 [9-(tetrahydro-2-furanyl)-9H-purin-6-amine; 10(-6) M], KCl (40 mM), or ouabain (10(-3) M) had no effect on isorhamnetin-induced vasodilation in the mesenteric bed. In permeabilized iliac arteries stimulated with Ca(2+) (pCa of 5.9), isorhamnetin was also significantly more potent (-log IC(50) = 5.27 +/- 0.15) than quercetin (-log IC(50) = 4.56 +/- 0.15). In conclusion, quercetin and its metabolites showed vasodilator effects with selectivity toward the resistance vessels. These effects are not due to or modulated by endothelial factors and are unrelated to changes in cytosolic Ca(2+).

Assessment of the antihypertensive and vasodilator effects of ethanolic extracts of some Colombian medicinal plants

The antihypertensive and vasodilator effects of ethanolic extracts prepared from Calea glomerata Klatt, Croton schiedeanus Schlecht, Curatella americana L., Lippia alba (Mill)n N.E.Br. and Lupinus amandus, which are medicinal plants used in Colombian folk medicine for the treatment of hypertension, were assayed both in SHR and Wistar rats and in rat isolated aortic rings. At a dose of 20 mg/kg, intravenous bolus administration of the ethanolic extracts, from C. schiedeanus, C. americana and L. amandus showed significant antihypertensive activity in SHR, C. schiedeanus being the most active. C. schiedeanus elicited dose-dependent decreases in mean arterial pressure and heart rate (5-100 mg/kg, i.v.) in SHR but 200 mg/kg administered orally did not show any significant effects, even after 3 h of observation. In intact rat aortic rings, ethanolic extracts from C. schiedeanus and Calea glomerata relaxed the contractions induced by KCl (80 mM) and phenylephrine (10(-6) M) in a concentration-dependent manner (10(-6)-3x10(-4) g/ml), with IC(50) of 6.5x10(-5) (7.3-5.8) g/ml and 7.1x10(-5) (7.9-6.4) g/ml, respectively. Bioguided phytochemical fractionation of the ethanolic extract from C. schiedeanus was started. More than one active principle seems to be present, flavonoids and terpenoids compounds were detected.

Antihypertensive and vasorelaxant effects of aqueous extract from Croton schiedeanus Schlecht in rats

Antihypertensive and vasorelaxant effects of treatment with the aqueous extract of Croton schiedeanus Schlecht (AECS) were investigated in anaesthetized spontaneously hypertensive rats (SHR). Intravenous bolus injections of AECS (5-100 mg/kg) elicited dose-dependent decreases in mean arterial pressure (MAP) and heart rate (HR). Additionally, AECS (10(-6)-3x10(-3)g/ml) completely relaxed the contractions induced by high K(+) concentrations in intact rat aortic rings in a concentration-dependent manner.

Modulatory effect of protein kinase C activator on contractility of rat vas deferens

The modulatory effect of the protein kinase C activator was examined on contraction of rat isolated vas deferens induced by constrictive agonists, noradrenaline (NA), ATP, BaCl2 and high K+. Phorbol 12,13-diacetate (PDA, 1 micromol/l) induced a transient extracellular Ca(2+)-dependent contraction while the inactive analogue, 4alpha-phorbol (1 micromol/l) had no effect. PDA significantly enhanced the peak amplitude of the contractile response to NA (0.1-10 micromol/l), ATP (100 micromol/l), Ba2+ (3 mmol/l) or high K+ (30 mmol/l). Staurosporine at 30 nmol/l reduced the enhancing effect of PDA on the agonist-induced contraction. NA (10 micromol/l) produced a phasic contraction followed by a sustained contraction, while ATP induced monophasic contraction. Pretreatment with nifedipine (10 nmol/l) had no effect on the phasic contraction induced by NA, but it significantly reduced ATP- or high K(+)-induced contraction. Staurosporine (30 nmol/l) alone attenuated the peak contractile response induced by NA or ATP but not by Ba2+. NA produced a transient contraction in Ca(2+)-free Krebs solution, and PDA (1 micromol/l) markedly enhanced this effect. These novel data indicate that activation of a protein kinase C-dependent mechanism not only affects contraction mediated by Ca2+ influx through voltage-sensitive Ca2+ channels, but also promotes intracellular Ca2+ release or intracellular Ca(2+)-mediated contractile mechanism in rat vas deferens.

Sedum telephium L. polysaccharide content affects MRC5 cell adhesion to laminin and fibronectin

In traditional medicine the fresh leaves and juice of Sedum telephium L. are used as wound-healing promoters. Cell adhesion represents a primary event in wound repair and in tissue homeostasis, and therefore we have investigated the effect of Sedum juice and its main fractions, polysaccharides and flavonols, on human fibroblast (MRC5) adhesion to fibronectin and laminin. Our findings revealed that total Sedum juice strongly inhibited cell adhesion to laminin and fibronectin (EC50 1.03+/-0.12 mg mL(-1)). This anti-adhesive feature was concentrated mainly in the two polysaccharide fractions (EC50 values comprised between 0.09 and 0.44 mg mL(-1)). The flavonol fractions did not seem to contribute to this effect. A first attempt to elucidate the polysaccharide-related anti-adhesive feature of Sedum juice was also performed. The results confirmed that natural polysaccharides, with chemical structures different from heparin, were able to interfere with integrin-mediated cell behaviour and they contributed to the outstanding effects of Sedum juice and to the role of polysaccharides in cell-matrix interaction.

Cardiovascular effects of captopril and enalapril in obese Zucker rats

The effects of two weeks of oral administration of the angiotensin-converting enzyme inhibitors captopril (a sulphydryl-containing drug) and enalapril (which lacks the sulphydryl group) on skeletal muscle glucose uptake, arterial blood pressure, cardiac hypertrophy, proteinuria and aortic vascular reactivity in obese Zucker rats were evaluated. Captopril (50 mg kg(-1) once daily) and enalapril (10 mg kg(-1) did not modify body weight gain or food or water intake. Both drugs decreased systolic blood pressure (157+/-6, 133+/-4 and 136+/-3 mm Hg, in vehicle-, captopril- and enalapril-treated rats, respectively), blood glucose (172+/-8 vs. 151+/-7 and 158+/-5 mg dl(-1), respectively), proteinuria (46+/-10 vs. 17+/-2 and 18+/-2.5 mg dl(-1), respectively) and heart weight (2.17+/-0.03, 1.98+/-0.02 and 1.99+/-0.04 mg g(-1)of body weight, respectively). Plasma insulin concentration was significantly increased by enalapril (17+/-2 ng ml(-1) vs. 9+/-2) but not by captopril (12+/-1). In the absence of insulin, the diaphragms from captopril- or enalapril-treated rats showed a significantly higher glucose uptake than that of controls (31% and 30% vs. control group, respectively). The presence of insulin in the incubation medium did not stimulate peripheral glucose uptake in the control group but significantly increased glucose uptake in diaphragms from captopril- or enalapril-treated rats (enhancement of glucose uptake vs. control: 52% and 43%, respectively). Endothelium-intact aortic rings from control Zucker rats showed a poor relaxant response to acetylcholine (maximal relaxation of 38.4+/-4.7%). Captopril significantly improved the endothelium-dependent vascular relaxation responses to acetylcholine and the endothelium-independent relaxation to the nitric oxide donor sodium nitroprusside whereas enalapril did not modify these relaxant responses. Neither captopril nor enalapril significantly affected the vascular contractile responses to the vasoconstrictors noradrenaline or KCl. In conclusion, the angiotensin-converting enzyme inhibitors captopril and enalapril reversed insulin resistance and the associated cardiovascular complications (cardiac hypertrophy, hypertension and proteinuria) in the obese Zucker rat, an animal model of non-insulin-dependent (type II) diabetes mellitus. However, only captopril, but not enalapril, improved the impaired endothelium-dependent and independent relaxant responses in the isolated rat aorta.

Depolarization-dependent effect of flavonoids in rat uterine smooth muscle contraction elicited by CaCl2

1. The effects of the flavonoids genistein (3-60 microM), kaempferol (3-60 microM) and quercetin (1-100 microM) on KCl (60 mM)-induced tonic contraction in rat uterus and their modifications with the inhibitor of cAMP-dependent protein kinases (TPCK, 3 microM), the inhibitor of ornithine decarboxylase [alpha-difluoromethyl ornithine (DFMO), 10 mM] and the polyamine spermine (1 mM) have been assayed. The effects of the three flavonoids were also studied on the contraction elicited by CaCl2 (30 microM to 10 mM) on rat uterus incubated in medium lacking calcium and supplemented with 33, 60 or 90 mM of KCl. For comparison, the effects of the calcium channel blockers nifedipine and verapamil and the activator of adenylyl cyclase forskolin were assayed on contractions induced by KCl and CaCl2. 2. Genistein (IC50: 20.2 +/- 1.0 microM, n = 11), kaempferol (IC50: 10.1 +/- 0.8 microM, n = 8) and quercetin (IC50: 13.2 +/- 0.5 microM, n = 8) relaxed the tonic contraction induced by KCl (60 mM) in a concentration-dependent way. Verapamil (IC50: 70.1 +/- 5.8 nM, n = 7), nifedipine (IC50: 8.4 +/- 0.7 nM, n = 6) and forskolin (IC50: 0.62 +/- 0.08 microM, n = 14) also relaxed the KCl-induced contraction. TPCK (3 microM) significantly antagonized the effect of quercetin, kaempferol and forskolin (P < 0.01) but did not modify the effect of genistein. 3. Spermine (1 mM) increased the effects of genistein and verapamil and antagonized the effect of quercetin but did not modify those of kaempferol and forskolin. DFMO (10 mM) did not modify the effect of quercetin but increased that of genistein and antagonized those of kaempferol and forskolin. The addition of spermine (1 mM) plus DFMO (10 mM) antagonized the effect of quercetin. Spermine counteracted the effect of DFMO on forskolin but not on genistein. 4. KCl (33, 60 or 90 mM) did not produce contraction in calcium-free solution, but CaCl2 (30 microM to 10 mM) induced concentration-dependent contraction after depolarizing with KCl. The EC50 values for CaCl2 were: 0.74 +/- 0.08 (n = 12), 0.34 +/- 0.03 (n = 14) and 0.48 +/- 0.02 (n = 12) mM in a medium with 33, 60 or 90 mM of KCl, respectively. 5. Genistein (20 microM), kaempferol (10 microM), quercetin (15 microM), verapamil (70 nM), nifedipine (10 nM) and forskolin (0.5 microM) inhibited the concentration-response curve to CaCl2 in medium supplemented with 33, 60 or 90 mM of KCl. The effect of kaempferol was independent of the concentration of KCl in the incubation medium. However, the inhibitory effect of genistein on CaCl2-induced contraction was inversely related to the concentration of KCl in the medium. On the contrary, the effect of quercetin was directly related to the concentration of KCl in the medium. 6. The antagonism of verapamil, nifedipine and forskolin on CaCl2-induced contraction seems to be related to the degree of depolarization because increasing the KCl in the medium counteracted their effects. 7. Our results suggest that (1) cAMP contributes to the relaxant effects of quercetin and kaempferol on KCl (60 mM)-induced tonic contraction; (2) polyamines are involved in the relaxant effects of forskolin and kaempferol on KCl-induced tonic contraction but not on CaCl2-induced contraction in the depolarized uterus, and (3) the flavonoids assayed also possess a calcium antagonist action but show a different behavior toward the calcium channel blockers and the cAMP enhancer forskolin.

Effect of tyrosine kinase and tyrosine phosphatase inhibitors on aortic contraction and induction of nitric oxide synthase

We studied the effects of the tyrosine kinase inhibitors genistein and tyrphostin and the tyrosine phosphatase inhibitors sodium orthovanadate and phenylarsine oxide on endotoxin-mediated induction of nitric oxide (NO) synthase in rat aorta and its effects on vascular contractility. Genistein (i.p. 10 mg/kg) inhibited the ex vivo vascular hyporesponsiveness to noradrenaline and the aminoguanidine-sensitive nitrite accumulation induced by endotoxin (i.p. 5 mg/kg) in aortic rings. Low concentrations of genistein (10(-6) M) and tyrphostin (3 x 10(-6) M) inhibited both endotoxin-induced hyporesponsiveness and nitrite and NOx accumulation in vitro in rat aorta without affecting control nitrite or NOx accumulation or contraction. Higher concentrations of genistein (10(-5) and 5.5 x 10(-5) M), sodium orthovanadate (10(-4) M) and phenylarsine oxide (10(-6) M) produced an irreversible depression of noradrenaline-induced contractions. In the presence of these drugs, endotoxin did not induce further depression of vascular contractility and did not increase nitrite or NOx production. In conclusion, there is a dissociation between the effects of these drugs on vascular smooth muscle contraction and NO synthase induction, the latter being more sensitive to inhibition by these drugs. Surprisingly, tyrosine phosphatase inhibitors produced similar effects to those of tyrosine kinase inhibitors, suggesting that there is a complex relationship between tyrosine kinases and phosphatases in the signalling pathway of agonist-induced vascular smooth muscle contraction and NO synthase induction.

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

1. Flavonoids produced a concentration-dependent relaxation of the contractile responses induced by noradrenaline, KCl, or phorbol 12-myristate-13-acetate in rat aortic rings. Only the flavonoid with three contiguous hydroxyls in B rings (myricetin), at low concentrations, potentiates the contractions evoked by these agonists. 2. The relaxant effects of flavanone on the noradrenaline-induced contractions were potentiated by isoprenaline and those of morin, chrysin, flavanone, and naringenin by sodium nitroprusside. 3. Several mechanisms are implicated in the vasodilatory effects of flavonoids: inhibition of protein kinase C; inhibition of cyclic nucleotide phosphodiesterases; and/or decreased Ca2+ uptake.

Vasodilator effects of visnagin in isolated rat vascular smooth muscle

Visnagin (4-methoxy-7-methyl-5H-furo [3,2-g][1]-benzopyran-5-one) is an active principle of the fruit of Ammi visnaga, a plant traditionally used in cardiovascular disorders. We have studied its vasodilator effects in rat vascular smooth muscle. The results demonstrated that visnagin inhibited the contractile responses induced in rat aortic rings by: (a) KCl or increases of extracellullar Ca2+ in KCl depolarized aortic rings, its effects being more potent against low (20 mM) than high (80 mM) KCl-induced contractions, (b) noradrenaline in Ca(2+)-containing solution and less effectively those in Ca(2+)-free solution and (c) phorbol 12-myristate 13-acetate (PMA) in a Ca(2+)-containing and with a lower potency in Ca(2+)-free medium. The relaxation induced by visnagin in aorta precontracted with noradrenaline was not affected by endothelium removal. Additionally, visnagin inhibited the spontaneous myogenic contractions of portal veins. The results showed that visnagin inhibited vascular smooth muscle contractility by acting at multiple sites. In the range of 10(-6) M to 5 x 10(-5) M visnagin appears to inhibit only the contractions mediated by Ca2+ entry through pathways with low sensitivity to classical Ca(2+)-entry blockers, i.e. agonist-, PMA- or mild depolarization-induced Ca2+ entry. Therefore, the vasodilator profile of visnagin, is not that of typical Ca(2+)-entry blockers which preferentially inhibit the contractions induced by strong depolarizations. At higher concentrations (> 5 x 10(-5) M) visnagin causes non-specific inhibition of vascular smooth muscle contractility.