Role of gap junction involved with endothelium-derived hyperpolarizing factor for the quercetin-induced vasodilatation in rat mesenteric artery.

AIMS: Modulation of vasodilating actions by quercetin, a kind of flavonoid, was investigated using rat mesenteric arterial ring strips. MAIN METHODS: Ring strips (1mm) of rat mesenteric artery were used. The specimens were kept at 36.5 °C in Krebs-Henseleit solution oxygenated with 95% O(2) and 5% CO(2). KEY FINDINGS: Quercetin (0.1 to 100 µM) dilated the contraction induced by norepinephrine (1 µM) in a concentration-dependent manner. The quercetin-induced vasodilatation was almost resistant to both 100 µM L-N(G)-nitro arginine methyl ester (L-NAME) and 100 µM indomethacin. At 1mM tetraethylammonium (a KCa channel inhibitor) decreased the quercetin-induced vasodilatation, which was resistant to L-NAME and indomethacin, but not significantly. L-NAME- and indomethacin-resistant quercetin-induced vasodilatation was significantly attenuated by 100 µM 18α- and 50 µM 18ß-glycyrrhetinic acids (gap junction inhibitors). Endothelium removal as well significantly attenuated the vasodilatation to the same extent. SIGNIFICANCE: These results indicate that quercetin dilates the mesenteric artery via endothelium-dependent mechanisms, and the dilatation is mainly mediated by gap junctions closely involved with endothelium-derived hyperpolarizing factor (EDHF).

Possible Involvement of Ca Activated K Channels, SK Channel, in the Quercetin-Induced Vasodilatation.

Effects of quercetin, a kind of flavonoids, on the vasodilating actions were investigated. Among the mechanisms for quercetin-induced vasodilatation in rat aorta, the involvement with the Ca(2+) activated K(+) (K(Ca)) channel was examined. Pretreatment with NE (5 microM) or KCl (60 mM) was carried out and then, the modulation by quercetin of the constriction was examined using rat aorta ring strips (3 mm) at 36.5. Quercetin (0.1 to 100 microM) relaxed the NE-induced vasoconstrictions in a concentration-dependent manner. NO synthesis (NOS) inhibitor, NG-monomethyl-L-arginine acetate (L-NMMA), at 100 microM reduced the quercetin (100 microM)-induced vasodilatation from 97.8+/-3.7% (n=10) to 78.0+/-11.6% (n=5, p<0.05). Another NOS inhibitor, L-NG-nitro arginine methyl ester (L-NAME), at 100 microM also had the similar effect. In the presence of both 100 microM L-NMMA and 10 microM indomethacin, the quercetin-induced vasodilatation was further attenuated by 100 microM tetraethylammonium (TEA, a K(Ca) channel inhibitor). Also TEA decreased the quercetin-induced vasodilatation in endothelium-denuded rat aorta. Used other K(Ca) channel inhibitors, the quercetin-induced vasodilatation was attenuated by 0.3 microM apamin (a SK channel inhibitor), but not by 30 nM charybdotoxin (a BK and IK channel inhibitor). Quercetin caused a concentration-dependent vasodilatation, due to the endothelium-dependent and -independent actions. Also quercetin contributes to the vasodilatation selectively with SK channel on smooth muscle.

Vascular modulation of rat aorta by taurine.

Taurine is found in high concentration in smooth muscle and heart muscle (approximately 10-20 mM). We found that taurine affects NE- and KCl-induced vasoconstriction. The mechanisms regulating these vasoconstrictions mostly involve Ca2+ channels and EDRF(NO). Taurine exerted either a vasodilation or vasoconstriction depending on cellular Ca2+ concentration. When vascular tone was excessively low, taurine promoted vasoconstriction allowing the maintenance of blood pressure. On the other hand, taurine dilates vessels to increase blood flow during ischemia or hypoxia. Thus, taurine modulates vascular wall tone to maintain blood flow. These results indicate that taurine plays an important homeostatic function on vascular smooth muscles as well as cardiac muscle.

Vascular pharmacology of mokuboito (mu-fang-yi-tang) and its constituents on the smooth muscle and the endothelium in rat aorta.

Pharmacological actions of Mokuboito and its constituents (Sinomenium acutum and sinomenine) on rat aorta were examined. Mokuboito and S. acutum at lower concentrations (0.03-1 mg ml(-1)) contracted the non-loaded aorta, but at higher concentrations (1-3 mg ml(-1)), reversed to dilate it. The vasoconstriction was blocked by phentolamine (10 muM). Sinomenine failed to exhibit the vasoconstriction. On the other hand, Mokuboito and S. acutum dilated the NE (5 muM)-induced vasoconstriction: at 3 mg ml(-1), by 98.9 +/- 2.5% (n = 6, P < 0.01) and 97.0 +/- 4.8% (n = 6, P < 0.01). Vasorelaxation induced by Mokuboito and S. acutum was attenuated by indomethacin, L-NMMA and nicardipine. Propranolol decreased the vasorelaxation induced by Mokuboito, but not by S. acutum. Sinomenine also relaxed the constriction and at 100 muM, by 68.8 +/- 5.1% (n = 7, P < 0.01). This vasorelaxation was attenuated by indomethacin, L-NMMA and nicardipine, and also by propranolol. Therefore, these results indicate that Mokuboito and its constituents exert both vasodilating actions mediated by endothelium-dependent mechanisms (PGI(2) and NO from endothelium) and by endothelium-independent mechanisms (Ca(2+) influx control on smooth muscle cells). Simultaneously, Mokuboito and S. acutum cause the vasoconstrictions mediated through alpha-adrenoceptor stimulation, but not sinomenine. Also, Mokuboito and sinomenine possess beta-adrenoreceptor stimulating action, but not S. acutum.

Cardiovascular pharmacology of sinomenine: the mechanical and electropharmacological actions.

Sinomenine is one of the alkaloids extracted from Chinese medical plant, Sinomenium acutum Rehder et Wilson. Sinomenine has been used for Rheumatoid arthritis as an anti-inflammatory and immunomodulative drugs. We have so far been investigated the cardiovascular pharmacological actions of sinomenine. Sinomenine dilated NE (5 µM)-, KCl (60 mM)- and PDB (300 nM)-induced vasoconstrictions. The pretreatment with nicardipine (0.1 µM), staurosporine (30 nM), L-NMMA (100 µM), indomethacin (10 µM) or propranolol significantly attenuated the sinomenine-induced vasorelaxation. Therefore, these results indicate that sinomenine causes the vasorelaxation by the involvement with the inhibitions of Ca(2+) current (I(Ca)) and PK-C, ß-adrenoceptor stimulation, and the activation of NO and PGI(2) syntheses in endothelium. On the other hand, in the ventricular cardiomyocytes of guinea pig, sinomenine inhibits I(Ca) and simultaneously decreases the delayed rectifier K(+) current (I(K)), resulting in the prolongation of action potential duration. Sinomenine also suppresses the dysrhysmias induced by triggered activities under the Ca(2+) overload condition. Therefore, sinomenine may be expected as one of effective therapeutic drugs for heart failure and dysrhythmias, and may maintain the cardiovascular functions due to modulation of cardiac ionic channels and blood vessels.

In vitro pharmacological actions of sinomenine on the smooth muscle and the endothelial cell activity in rat aorta.

Vasodilating actions of sinomenine were examined using rat aorta ring strips. Sinomenine (0.1 to 100 microM) dilated norepinephrine (NE, 5 microM)-induced vasoconstriction in a concentration-dependent manner reaching 68.8+/-5.1% (n=6, P<0.01) at a concentration of 100 microM. Sinomenine (100 microM) also attenuated KCl (60 mM) and phorbol 12, 13-dibutyrate (PDB, a protein kinase C, PK-C, activator, 300 nM)-induced vasoconstriction by 86.9+/-8.5% (n=6, P<0.01) and 49.9+/-9.8% (n=6, P<0.01), respectively. Pretreatment with nicardipine (a Ca2+ channel antagonist), staurosporine (a PK-C inhibitor), NG-monomethyl-L-arginine acetate (L-NMMA, a nitric oxide, NO, synthesis inhibitor), and indomethacin (a cyclooxygenase inhibitor) were carried out. Nicardipine (0.1 microM) led to a significant decrease in the vasodilating potential of sinomenine (at 100 microM, 68.8+/-5.1% vs. 35.5+/-6.9%; n=5, P<0.001). Pretreatment with staurosporine (30 nM) reduced sinomenine-associated vasodilation from 68.8+/-5.1% to 49.5+/-7.7% (n=5, P<0.001), and L-NMMA (100 microM) and indomethacin (10 microM), to 25.3+/-2.3% (n=5, P<0.001) and to 37.1+/-9.3% (n=5, P<0.001), respectively. The responses were almost similar to the results without endothelium. Therefore, these results indicate that sinomenine causes the vasorelaxation by the mechanisms involved with the inhibitions of Ca2+ channel and PK-C activity, and also with the activations of NO and prostaglandin (PG) I2 syntheses in endothelium.

Age-related changes in the vasodilating actions of Ginkgo biloba extract and its main constituent, bilobalide, in rat aorta.

BACKGROUND: Age-related modulation in vasodilating actions induced by Ginkgo biloba extract (GBE) and bilobalide, a main constituent of GBE, were examined using rat aorta ring strips. METHODS: Wistar rats from 5 to 25 weeks old were used, and the isolated aorta ring strips were fixed in Krebs-Henseleit solution. RESULTS: GBE and bilobalide concentration-dependently dilated norepinephrine (NE)-induced vasoconstriction in all aged rats. The vasodilating actions generally decreased in accordance with aging. GBE at 1 mg/ml decreased from 28.4+/-3.8% (n=5) in 5-week-old rats to 23.7+/-7.1 (n=7) in 25-week-old rats, but not significantly. GBE (3 mg/ml)-induced vasodilation was maximum by 73.7+/-2.1% (n=4, P<0.001) in 10-week-old rats. GBE had the marked vasodilation at younger ages and further decreased it with developing ages. In the rats older than 20 weeks, however, GBE tended to rather increase the strength of vasodilating action. On the other hand, the vasorelaxation induced by 30 micromol/l bilobalide significantly decreased from 11.8+/-1.4% (n=4) in 5-week-old rats to 2.3+/-1.5% (n=5, P<0.01) in 25-week-old rats, and by 100 micromol/l from 20.2+/-3.4% (n=4) to 5.6+/-2.5% (n=5, P<0.01), respectively. Bilobalide had the similar age-related actions. The age-dependent attenuation was produced milder by bilobalide than by GBE. At lower concentrations, however, bilobalide caused the weak vasocontriction in 20- and 25-week-old rats. CONCLUSION: GBE and bilobalide possess a similar characteristic for age-related modification, clinically suggesting the more effective actions of GBE for elder persons.

Electropharmacological actions of Ginkgo biloba extract on vascular smooth and heart muscles.

Ginkgo biloba extract (GBE) is composed mostly of two constituents: One is terpenoids (such as bilobalide, ginkgolides A, B and C), and the other is flavonoids (such as quercetin and rutin). After oral administration of GBE (160 mg) to healthy volunteers, the plasma concentrations of ginkgolides A and B and bilobalide are 41.8, 5.6 and 37.6 ng/ml, respectively. GBE and bilobalide cause a potent concentration-dependent relaxation. NG-Monomethyl-l-arginine acetate (l-NMMA), an NO synthesis inhibitor, reduces the vasodilation induced by GBE. Furthermore, the vasorelaxation of GBE is attenuated in Ca2+-free medium. Bilobalide possesses similar mechanisms. The other constituents also produce vasorelaxation. On the other hand, all the compounds markedly modify the action potential configuration in guinea pig ventricular cardiomyocytes. GBE prolongs the action potential duration (APD), whereas bilobalide shortens the APD. In patch-clamp experiments, GBE markedly inhibits the Ca2+ current (ICa), the delayed rectifier K+ current (IK) and the inwardly rectifying K+ current (IK1). On the contrary bilobalide enhances the ICa and IK currents concentration-dependently. The other constituents do not cause their actions in a uniform direction. In the rat sino-atrial (SA) node, GBE causes a negative chronotropic effect. These results indicate that GBE and the constituents produce effective electropharmacological actions in the cardiomyocytes and cause vasodilation, mainly due to the inhibitions of Ca2+ influx through the Ca2+ channel and the activation of NO release in the endothelium and aortic vascular muscles.

Comparative vasodilating actions among terpenoids and flavonoids contained in Ginkgo biloba extract.

BACKGROUND: Comparative vasodilating actions of the constituents of Ginkgo biloba extract (GBE), terpenoids (bilobalide, ginkgolides A, B and C) and flavonoids (quercetin and rutin), were examined using rat aorta ring strips. METHODS: Cumulative administrations of GBE and its constituents were followed with the pretreatment of 5 micromol/l NE. RESULTS: GBE at 0.03 to 3 mg/ml had a potent concentration-dependent relaxation; by 70 +/- 4.5% (n = 6, P < 0.001) at 3 mg/ml. Terpenoids and flavonoids at 0.1 to 100 micromol/l had potent concentration-dependent relaxation. At 100 micromol/l, bilobalide dilated by 17.6 +/- 3.9% (n = 7, P < 0.05), and ginkgolides A, B and C also caused it to the almost same extent. Quercetin (100 micromol/l) caused a potent vasorelaxation by 49.9 +/- 4.8% (n = 10, P < 0.001). Rutin at 100 micromol/l had weaker vasorelaxation; by 13.7 +/- 3.2% (n = 6, P < 0.01). CONCLUSIONS: All constituents of GBE have the concentration-dependent vasorelaxtant effect. The potency of GBE's action was not made simply by addition of those of the constituents. Each constituent itself would contribute to the GBE-induced vasodilation, although the constituents have the complicated interactions with each other.

Mechanisms for the vasodilations induced by Ginkgo biloba extract and its main constituent, bilobalide, in rat aorta.

Vasodilating actions of Ginkgo biloba extract (GBE) and bilobalide, a main constituent, were examined using rat aorta ring strips. GBE at the concentration ranges from 0.03 to 3 mg/ml had a potent concentration-dependent relaxation, reaching 70 +/- 4.5% (n = 6, P < 0.001) at 3 mg/ml. Bilobalide at 0.1 to 100 microM also caused the relaxation in a concentration-dependent manner. At 100 microM, bilobalide caused dilation by 17.6 +/- 3.9% (n = 7, P < 0.05). NG-monomethyl-L-arginine acetate (L-NMMA)(100 microM), an NO synthesis inhibitor, reduced the vasodilation of GBE (3 mg/ml) to 57.6 +/- 2.5% (n = 6, P < 0.05), and was accompanied with a decrease in the rate of relaxation. Tetraethylammonium (TEA)(100 microM), a Ca(2+)-activated K(+) channel inhibitor, also decreased the GBE (3 mg/ml)-induced relaxation to 63.1 +/- 4.6% (n = 6), but not significantly. Indomethacin tended to reduce the GBE (3 mg/ml)-induced vasorelaxation to 67.3 +/- 4.1% (n = 6). In contrast, the vasorelaxation of GBE (3 mg/ml) was strongly attenuated to 53 +/- 6.1% (n = 7, P < 0.05) in Ca(2+)-free medium. Similarly, the vasorelaxation induced by bilobalide significantly decreased both by pretreatment with NO inhibitor (L-NMMA) and in Ca(2+)-free solution. These results indicate that the relaxation induced by GBE would be due to the inhibition of Ca(2+) influx through the Ca(2+) channel and the activation of NO release, and might be in part due to the inhibitions of Ca(2+)-activated K(+) current and PGI(2) release, in the endothelium and aortic vascular muscles. Bilobalide possesses the similar mechanisms for the vasodilation.