Relaxant effects of the neutral extract of the leaves of Bidens pilosa Linn on isolated rat vascular smooth muscle

The long-lasting antihypertensive effect of a neutral extract of Bidens pilosa has been suggested to be due to vasodilation. The present work was undertaken to assess this hypothesis. The vasorelaxant effect of a neutral extract (NBp) of the leaves of B. pilosa was evaluated in vitro on isolated rat aorta contracted with KCl or norepinephrine. NBp induced a concentration-dependent vasorelaxation of the rat aorta precontracted with KCl (60 mM) by 25%-105% at the respective concentrations of 0.25-1.5 mg/mL. The maximal concentration of 1.5 mg/mL provoked 88% relaxation of norepinephrine-induced contractions. There were no significant differences between the effects of the extract on the aorta strips with or without endothelium. In the presence of indomethacin or pyrilamine maleate, the relaxant response induced by the plant extract was significantly inhibited at the lower concentrations. The plant extract was able to reduce the aorta resting tone, inhibit the KCl-induced contractions (90% at 1.5 mg/mL) and the CaCl2-induced contractions by 95% at a concentration of 0.75 mg/mL. These results demonstrate the vasodilating properties of the neutral extract of Bidens pilosa and indicate that it may act as a calcium antagonist.     

Vasorelaxant effect of stilbenes from rhizome extract of rhubarb (Rheum undulatum) on the contractility of rat aorta

The vascular relaxant effect of the rhizome extract of Rheum undulatum was evaluated with isolated rat thoracic aorta preparations. The methanol extract of the rhizome induced a concentration-dependent relaxation of aortic preparations precontracted with 0.3 microm phenylephrine (EC50 value: 5.8 microg/mL). The activity-guided fractionation of the extract led to the isolation of seven hydroxystilbene components as active principles, i.e. piceatannol, resveratrol, desoxyrhapontigenin, rhapontigenin, piceid, rhaponticin and epsilon-viniferin. Of these, piceatannol, a tetrahydroxystilbene, exhibited the most potent vascular relaxant effect in rat aortic preparations (EC50 value 2.4 microm). The vasorelaxant effect of piceatannol on endothelium-intact aorta rings was diminished completely by the removal of functional endothelium or by pretreatment of the aortic tissues with N(G)-nitro-l-arginine methyl ester. These results suggest that piceatannol may be the major mediator responsible for the vasorelaxing properties of the rhizome extract of Rheum undulatum and the vasorelaxant effects of the piceatannol may be mediated via endothelium-dependent nitric oxide signaling pathway.     

Vascular action of the crude hydroalcoholic extract from Hymenaea martiana on the isolated rat and rabbit aorta

The present study investigates the effect of the hydroalcoholic extract (HE) from Hymenaea martiana (Leguminosae) on endothelium-dependent and independent relaxation responses induced by acetylcholine (ACh), histamine (His), calcium ionophore (A23187) and sodium nitroprusside in precontracted aortic rings from rat and rabbit. In addition, we have also evaluated the action of the HE on noradrenaline- (NA), angiotensin I-(AI) and AII-induced contractions in the rabbit aorta. The HE (0.25–0.5 mg/mL) inhibited in a concentration-dependent manner the relaxant response induced by ACh in rings of rabbit aorta and by His in rat aorta. Relaxation in response to A23187 was inhibited in rat but not in rabbit aortic rings. In contrast, the HE was completely ineffective against endothelium-independent relaxations caused/by sodium nitroprusside in rabbit aorta rings. The HE (0.5–1.0 mg/mL) significantly enhanced the maximal contractile responses induced by NA in rabbit aorta set up with the endothelium, but caused no effect in endothelium rubbed preparations. In addition, the HE (0.5 mg/mL) markedly antagonized the contractile responses elicited by AI, but caused only a slight effect on AII-induced contractile responses in rabbit aorta. These findings indicate that the active principle(s) present in the HE from the bark of Hymenaea martiana selectively inhibit the endothelium-dependent vasorelaxant responses caused by several substances in aortic rings from rat and rabbit, presumably by a mechanism related with endothelium-derived relaxation factor synthesis and/or inactivation. The HE also antagonized AI but not AII-induced contractions in rabbit aorta, suggesting some interference with the angiotensin converting enzyme.     

Vasorelaxant effects of Brillantaisia nitens Lindau (Acanthaceae) extracts on isolated rat vascular smooth muscle

Brillantaisia nitens Lindau (Acanthaceae) is traditionally used in Cameroon for the treatment of many diseases including cardiovascular disorders. We have studied its vasorelaxant effects in rat vascular smooth muscle. In this study, aqueous, methylene chloride, methanol, and methylene chloride/methanol leaves extracts of Brillantaisia nitens were tested for their relaxing ability in vitro. Strips of rat aorta, with or without intact endothelium, were mounted in tissue baths, contracted with KCl (60mM) or norepinephrine (10(-4)M), and then exposed to the plant extracts. These extracts exhibited concentration-dependent vasorelaxations of norepinephrine-induced contractions of intact aortic strips. The EC(50) were 0.42+/-0.01mg/ml (aqueous extract), 0.63+/-0.02mg/ml (methylene chloride extract), 0.73+/-0.02mg/ml (methanol extract) and 0.36+/-0.02mg/ml (methylene chloride/methanol extract). The methylene chloride/methanol (CH(2)Cl(2)/CH(3)OH) extract was the most potent relaxing extract. It caused a concentration-dependent and endothelium-independent relaxation of the rat aortic strips contracted by KCl or norepinephrine. On the NE-induced contraction, its maximal relaxant activity (109%) due to the dose of 1.5mg/ml, was not significantly modified by the pretreatment of aortic strips with indomethacin (89%, P>0.05) or with l-NAME (103%, P>0.05). This suggests that the vasorelaxation elicited by CH(2)Cl(2)/CH(3)OH extract was not mediated via endothelium-derived prostacyclin or nitric oxide. In contrast, this relaxation was markedly reduced by tetraethylammonium, a blocker of non-selective K(+) channels and glibenclamide, a blocker of ATP-sensitive K(+) channels. The CH(2)Cl(2)/CH(3)OH extract significantly inhibited Ca(2+)-induced concentration-contraction and the Ca(2+) influx in aortic strips incubated with 60mM KCl. These results indicate that the vasorelaxant effect of the CH(2)Cl(2)/CH(3)OH extract of Brillantaisia nitens is due to an inhibition of Ca(2+) influx, possibly via the activation of ATP-sensitive K(+) channels.     

Vasodilator Effects of the Extract of the Leaves of Cistus populifolius on Rat Thoracic Aorta

The effects of different extracts of Cistus populifolius L. on smooth muscle were studied. The aqueous extract inhibited in a dose dependent manner the noradrenaline (NA) (10⁻⁹–1.03×10⁻⁶ MSC ) and CaCl₂ (2×10⁻⁴–1.28×10⁻² MSC )-induced contractions in rat thoracic aorta. Furthermore, this extract induced relaxant effects in rat aorta precontracted with NA (10⁻⁶ MSC ) and with K⁺ (80 mMSC ). Two different vasodilator responses were observed on NA-induced contractions: one an endothelium-dependent response abolished by methylene blue but not by indomethacin, and the other an endothelium-independent response unaffected by methylene blue and indomethacin similar to that obtained with a flavone, luteolin (10⁻⁵ MSC ). The search for active constituents included a bioactivity-directed fractionation of the lyophilized aqueous extract (LAE) using vascular reactivity experiments. Four different fractions (Cl₂CH₂, Me₂CO, MeOH, H₂O) were analysed at two different concentrations (1 and 2 mg (dry plant)/mL). The methanol fraction was the most active on NA precontracted vascular segments with endothelium, whereas the water fraction was the most active on segments without endothelium. These relaxant effects were less on K⁺ (80 mMSC )-induced contractions. Due to these results we suggest that this plant contains interesting hydrophilic compounds with strong pharmacological action. The endothelium-independent relaxant effect is probably related to flavonoid constituents. However we cannot relate the endothelium-dependent relaxation to known natural compounds in Cistus species. The presence of these constituents with relaxing properties on smooth muscle could account for the use of Cistus plant in traditional medicine.     

五种中药提取物的血管活性作用实验研究

目的:观察川芎、大蓟、元参、红花和绞股蓝抽提物的血管活性作用。同时研究了绞股蓝的正丁醇、氯仿及水提取物对离体血管的影响。方法:实验是在有内皮和无内皮的离体大鼠主动脉上完成的。离体大鼠主动脉置于浴槽内,各种中药提取物所引起的血管张力改变被测定。结果:除红花外,其他4种中药引起剂量依赖性舒张作用,内皮存在时舒张反应更明显。绞股蓝的正丁醇提取物引起内皮依赖性扩张反应。而氯仿及水提取物无血管活性作用。结论:川芎、大蓟、元参、绞股蓝可引起内皮源舒张因子增加。红花无此作用。     

Antispasmodic effect of three fractions of hydroalcoholic extract of Pycnocycla spinosa

Hydroalcoholic extract of Pycnocycla spinosa was shown to have spasmolytic action in vitro and antidiarroheal effect in vivo. The hydroalcoholic extract of P. spinosa is composed of alkaloid-, flavonoid- and saponin-rich components. These components were separated by fractional separation technique. The pharmacological objective of this study was to look for relaxant effect of these components of hydroalcoholic extract of P. spinosa on rat isolated ileum contractions. The alkaloid-, flavonoid- and saponin-rich fractions of P. spinosa inhibited the response to 80 mM KCl in a concentration-dependent manner. The alkaloid-rich fraction was the most and saponin-rich fraction the least effective relaxant of ileum contractions. The alkaloid-rich fraction also inhibited the response to acetylcholine (ACh) and 5-hydroxytryptamine (5-HT). From this study, it can be concluded that the antispasmodic action of hydroalcoholic extract of P. spinosa could be due to components in the alkaloid-rich fraction and to a lesser extent, to its flavonoid-rich fraction.     

Inhibition of Histamine-induced Contraction of Rat Ileum by Promethazine and the Methanol Stembark Extract of Erythrina sigmoidea (Hua)

Histamine, a potent H₁ and H₂ receptor agonist provoked dose dependent contractions of the rat ileal strip. The contractile effect was reduced by almost 54.6% when challenged with 1.8 μg/mL of the stembark extract of Erythrina sigmoidea (ES) while 4.8 μg/mL of the plant extract completely abolished 10⁻⁴ Msc histamine-induced contraction. A similar relaxant effect was obtained with 0.5 μg/mL promethazine, a potent H₁ blocker, but this relaxant effect was less significant compared with that of the plant extract.     

Endothelium-dependent induction of vasorelaxation by the butanol extract of Phellinus igniarius in isolated rat aorta

The butanol extract of Phellinus igniarius (BPI) induced relaxation of the phenylephrin e-precontracted rat aorta in a dose-dependent manner, and its effect was abolished by the removal of functional endothelium. Pretreatment of the aortic tissues with N(G)-nitro-L-arginine methyl ester (L-NAME), methylene blue, or 1H-[1,2,4]-oxadiazole-[4,3-alpha]-quinoxalin1-one (ODQ) inhibited the vascular relaxation induced by BPI. BPI-induced vascular relaxations were also markedly attenuated by the addition of verapamil or diltiazem, while the relaxant effect of BPI was not blocked by pretreatment with indomethacine, glibenclamide, tetraethylammonium (TEA), atropine, or propranolol. Incubation of endothelium-intact rat aorta with BPI increased the production of cGMP in a dose-dependent manner. These results suggest that BPI dilates vascular smooth muscle via endothelium-dependent nitric oxide-cGMP signaling pathway, with the possible involvement of L-type Ca(2+) channels.     

葛根素的非内皮依赖性血管舒张作用机制

目的 :研究葛根素对血管的舒张作用并探讨其机制。方法 :记录离体大鼠胸主动脉环张力反应。结果 :葛根素能明显舒张由苯肾上腺素诱导收缩的大鼠主动脉环 ,其血管舒张作用为非血管内皮依赖性 ;KCl预收缩下 ,葛根素对主动脉环无舒张作用。对去内皮的血管环 ,在无Ca²⁺ 溶液中 ,葛根素不能够抑制咖啡因或苯肾上腺素诱导的短暂收缩。钾通道阻断剂 4 氨基吡啶和四乙胺孵育后能够明显抑制葛根素的舒张血管\作用 ,但格列苯脲不能抑制其舒张血管作用。结论 :葛根素的血管舒张作用是非内皮依赖性的 ,其机制可能是通过抑制α肾上腺素受体介导的血管平滑肌细胞外Ca²⁺ 内流而起作用的。同时 ,KV 通道和ATP敏感性K⁺ 通道参与了葛根素的舒血管作用。     

Relaxant effect of essential oil and hydro-alcoholic extract of Pycnocycla spinosa Decne. exBoiss. on ileum contractions

Pycnocycla spinosa is an essential oil from a wild plant growing in central Iran. However, so far its pharmacological effects have not been studied. The aim of this study was to look for relaxant effects of the essential oil and hydro-alcoholic extract of P. spinosa on rat isolated ileum contractions induced by KCl and acetylcholine (ACh). P. spinosa essential oil (PSEO) and the hydro-alcoholic extract inhibited the response to 80 mM KCl in a concentration-dependent manner and attenuated the maximum attainable response of ACh concentration-response curve. Furthermore, in caster oil induced diarrhoea, the hydro-alcoholic extract had a dose-dependent anti-diarrhoeal effect. This study showed that P. spinosa essential oil and its hydro-alcoholic extract act as a relaxant of rat isolated ileum. As the inhibition of contractile over-activity of the ileum is the basis for the treatment of gastro-intestinal disorders such as diarrhoea, P. spinosa may have clinical bene fi ts for treatment of this condition.     

补肾活血浸膏的舒张血管作用及其机理研究

目的:通过观察补肾活血浸膏对豚鼠肠系膜微血管、大鼠胸主动脉环、门静脉环及其血浆的NO、血管的NO和NOS、cNOS、iNOS的影响,研究本方的舒张血管作用及其效应机制.方法:去甲肾上腺素致豚鼠肠系膜微血管收缩研究其整体的舒张血管作用;观察药物对苯肾上腺素收缩离体大鼠胸腔主动脉环或静脉环的作用,以及在预加优降糖或普萘洛尔或去血管内皮后其作用的影响;硝酸还原酶法测定给予药物后大鼠血浆和血管的NO及血管NOS、cNOS、iNSO的含量变化.结果:补肾活血浸膏有扩张去甲肾上腺素致豚鼠肠系膜微血管收缩的作用;松弛苯肾上腺素引起的离体大鼠胸腔主动脉环或静脉环的收缩作用,预加优降糖仍然有松弛作用.然而对预加普萘洛尔后补肾活血浸膏剂量低时保持舒张血管作用,剂量增加时反而引起收缩血管作用,大鼠胸腔主动脉环去内皮后药物无松弛作用,反而引起收缩作用;补肾活血浸膏高、低剂量组均能升高血浆NO水平,但只有高剂量组有显著性差异(P＜0.01);高、低剂量组均能显著性升高大鼠主动脉NO(P＜0.001,P＜0.05);高剂量组显著性升高NOS(P＜0.05)和cNOS(P＜0.001),低剂量组有升高NOS作用,但无显著性差异,对cNOS有显著性升高作用.结论:补肾活血浸膏的舒张血管作用机制与血管内皮释放NO和促进NOS、cNOS合成有关.     

Mechanisms of the anti-hypertensive effect of Hibiscus sabdariffa L. calyces

Previous studies have demonstrated the anti-hypertensive effects of Hibiscus sabdariffa L. (HS) in both humans and experimental animals. To explore the mechanisms of the anti-hypertensive effect of the HS, we examined the effects of a crude methanolic extract of the calyces of HS (HSE) on vascular reactivity in isolated aortas from spontaneously hypertensive rats. HSE relaxed, concentration-dependently, KCl (high K(+), 80 mM)- and phenylephrine (PE, 1 microM)-pre-contracted aortic rings, with a greater potency against the alpha(1)-adrenergic receptor agonist. The relaxant effect of HSE was partly dependent on the presence of a functional endothelium as the action was significantly reduced in endothelium-denuded aortic rings. Pretreatment with atropine (1 microM), L-NAME (10 microM) or methylene blue (10 microM), but not indomethacin (10 microM), significantly blocked the relaxant effects of HSE. Endothelium-dependent and -independent relaxations induced by acetylcholine and sodium nitroprusside, respectively, were significantly enhanced in aortic rings pretreated with HSE when compared to those observed in control aortic rings. The present results demonstrated that HSE has a vasodilator effect in the isolated aortic rings of hypertensive rats. These effects are probably mediated through the endothelium-derived nitric oxide-cGMP-relaxant pathway and inhibition of calcium (Ca(2+))-influx into vascular smooth muscle cells. The present data further supports previous in vivo findings and the traditional use of HS as an anti-hypertensive agent.     

Studies on the vascular effects of the fractions and phenolic compounds isolated from Viscum album ssp. album

Viscum album L. has been used in the indigenous system of medicine for treatment of various diseases such as atherosclerosis and hypertension. In the literature, phenylpropan and flavonoid derivatives were suggested to play a role in the inhibition of cyclic adenosine monophosphate (cAMP)-phosphodiesterase (PDE) and a correlation was proposed between the in vitro inhibition of PDE and in vivo pharmacological activity. The vascular effects of the phenolic compounds and subfractions isolated from n-butanolic fraction of V. album ssp. album were studied on noradrenaline-contracted rat aortic rings. Isolated phenolic compounds (Syringin (VA-1), Coniferin (VA-9), 5, 7-dimethoxy-flavanone-4'-O-[beta-D-apiofuranosyl(1-->2)]-beta-D-gl uco pyranoside (VA-4)) produced concentration-dependent contractions in rat aortic rings. Only one compound (Kalopanaxin D (VA-15)) displayed very slight relaxant response. The weak concentration-dependent relaxing effect of the subfractions gave the idea that vasodilator activity were observed in the less polar subfractions. In addition, there was no clear correlation between the weak relaxant effects of subfractions and an inhibitory effect on cAMP-PDE.     

白藜芦醇对大鼠离体胸主动脉环的舒张作用

目的:观察白藜芦醇(resveratrol,RVL)对大鼠离体胸主动脉血管的舒张作用并探讨其机制。方法:采用离体血管环灌流方法,观察RVL在含Ca²⁺或无Ca²⁺ Krebs液孵育条件下对去甲肾上腺素(NA)引起的血管平滑肌收缩的影响;同法观察RVL对30,80mmol·L^-1的KCl引起的血管平滑肌收缩的影响;RVL对NA引起的依赖于细胞内钙和细胞外钙收缩反应的影响,以及加入N-G-硝基-L-精氨酸(L-NNA)和优降糖后RVL舒张大鼠离体主动脉环效应的变化。结果:RVL呈浓度依赖性舒张NA引起的血管收缩;无Ca²⁺ 组RVL抑制NA所致血管平滑肌收缩效应大于含Ca²⁺ 组;RVL能够拮抗NA诱发的依内钙的收缩反应,而对外钙收缩无抑制。RVL对80,30mmol·L^-1 的KCl引起的血管平滑肌收缩均有抑制作用,且前者量效曲线明显上移。L-NNA使RVL舒血管效应降低(26.0±4.6)%;优降糖组的血管舒张受抑程度与对照组无显著差别(P>0.05)。结论:RVL可呈内皮依赖性舒张血管平滑肌,其作用机制可能与该药促进NO合成释放,开放钙激活的钾通道以及抑制血管平滑肌细胞外钙内流和内钙释放有关。     

Effects of the ethanolic extract of Spirulina maxima on endothelium dependent vasomotor responses of rat aortic rings

Dietary Spirulina decreases, endothelium-dependently, the responses to vasoconstrictor agonists and increases the endothelium-dependent, agonist-induced, vasodilator responses of rat aorta rings. The aim of this study was to analyze, in vitro, the effects of a raw ethanolic extract of Spirulina maxima on the vasomotor responses of rat aortic rings to phenylephrine and to carbachol. On rings with endothelium, the extract produced the following effects: (a) a concentration-dependent (60-1000 microg/ml) decrease of the contractile response to phenylephrine; (b) a rightward shift and a decrease in maximal developed tension, of the concentration--response curve to phenylephrine; (c) a concentration dependent relaxation of phenylephrine-precontracted rings. These effects were blocked by L-NAME, and not modified by indomethacin. The extract had no effect on the concentration-response curve to carbachol of rings with endothelium. On endothelium-denuded rings the extract caused a significant rightward shift of the concentration response curve to phenylephrine without any effect on maximal tension development. In the presence of the extract, indomethacin induced a marked decrease in the maximal phenylephrine-induced tension of endothelium-denuded rings. These results suggest that the extract increases the basal synthesis/release of NO by the endothelium and, also, the synthesis/release of a cyclooxygenase-dependent vasoconstricting prostanoid by vascular smooth muscle cells.     

杜仲木脂素化合物舒张血管作用机制

目的：观察杜仲木脂素部位（EUL）对血管的舒张作用并探讨其机制。方法：以大鼠胸主动脉为标本,观察EUL对NE,KCl预收缩血管的舒张作用及对血管内皮细胞、血管平滑肌作用的影响。结果：EUL能显著舒张NE预收缩的血管,内皮去除后,该作用明显降低；KCl收缩下,EUL对主动脉环无明显舒张作用。去内皮的血管,EUL对NE在无Ca²⁺ 液中收缩幅度没有影响；使NE的量效曲线非平行右移,最大反应降低。钾通道阻断剂格列本脲孵育后能明显抑制EUL的舒血管作用。结论：杜仲木脂素部位有明显的舒血管作用,其机制与内皮依赖性有关。同时ATP敏感性K⁺ 通道也参与了EUL的舒血管作用。     

Antispasmodic and hypotensive effects of Ferula asafoetida gum extract

The effects of Ferula asafoetida gum extract on the contractile responses of the isolated guinea-pig ileum induced by acetylcholine, histamine and KCl, and on the mean arterial blood pressure of rat were investigated. In the presence of extract (3 mg/ml), the average amplitude of spontaneous contractions of the isolated guinea-pig ileum was decreased to 54 +/- 7% of control. Exposure of the precontracted ileum by acetylcholine (10 microM) to Ferula asafoetida gum extract caused relaxation in a concentration-dependent manner. Similar relaxatory effect of the extract was observed on the precontracted ileum by histamine (10 microM) and KCl (28 mM). However, when the preparations were preincubated with indomethacin (100 nM) and different antagonists, such as propranolol (1 microM), atropine (100 nM), chlorpheniramine (25 nM) then were contracted with KCl, exposure to the extract (3 mg/ml) did not cause any relaxation. Furthermore, Ferula asafoetida gum extract (0.3-2.2 mg/100g body weight) significantly reduced the mean arterial blood pressure in anaesthetised rats. It might be concluded that the relaxant compounds in Ferula asafoetida gum extract interfere with a variety of muscarinic, adrenergic and histaminic receptor activities or with the mobilisation of calcium ions required for smooth muscle contraction non-specificly.     

Vasodilator effect of the extracts and some coumarins from the stem bark of Mammea africana (Guttiferae)

CH(2)Cl(2) fraction obtained from the stem bark of Mammea africana inhibited noradrenaline (NA) or KCl-induced contraction in isolated guinea pig and rat aorta. The vasorelaxant potency of the CH(2)Cl(2) fraction of Mammea africana was diminished by a pre-treatment with Nitro-L-arginine methyl ester (L-NAME), an inhibitor of NO synthase, which was however not affected by indomethacin pre-treatment. These findings indicated that the vasorelaxant effect of Mammea africana may be partially endothelium dependent, mediated by nitric oxide and that vasoactive prostanoids might not be contributing to the vasorelaxation effect. Three bioactive compounds were isolated from this CH(2)Cl(2) fraction and identified as 4-n-propylcoumarins (1) (mammea B/BB), 4-phenylcoumarins (2) (mammea A/AA or mammeisin) and (B/BA) (3) and might involved in the vasorelaxant effect of the extract. The mechanisms of the vasorelaxant effect might therefore be multiple, including endothelium dependence and the mechanisms, which interfere with the liberation of Ca(2+) into the muscle cell.     

Role of nitric oxide in the vasorelaxant and hypotensive effects of extracts and purified tannins from Geum japonicum

Crude extracts and three purified tannins from Geum japonicum Thunberg (Rosaceae) were examined for relaxant effects in isolated rat thoracic aorta and for hypotensive effects in anesthetized normotensive and hypertensive rats. The acetone extract and the butyl alcohol extract of Geum japonicum at a cumulative concentration of 30mug/ml potently relaxed phenylephrine-precontracted aortic rings by 73+/-5% and 80+/-7%, respectively, without affecting the resting tension of these vessels. Removal of the vascular endothelium, inhibition of nitric oxide (NO) synthase with N(omega)-nitro-l-arginine (l-NA) or inhibition of cGMP biosynthesis with methylene blue all abolished the vasorelaxant effects of the Geum japonicum extracts. Addition of l-arginine, the substrate for NO biosynthesis, reversed the inhibitory effects of l-NA. Similar vasorelaxant effects of 82+/-10%, 61+/-8% and 82+/-14%, were observed with the purified tannins, penta-O-galloyl-beta-glucoside, casuariin and 5-desgalloylstachyurin, respectively, at a cumulative concentration of 10muM. Intravenous injection of the butyl alcohol extract of Geum japonicum at a cumulative dose of 2.5mg/kg into both hypertensive and normotensive rats resulted in a marked reduction in the mean arterial blood pressure by 46+/-6% and 34+/-7%, respectively, which was abolished by prior injection of l-NA. Therefore, these results suggest that tannins may be responsible for the vasorelaxant and hypotensive effects of Geum japonicum, mediated via endogenous NO and subsequent cGMP formation. The data suggest that extracts of Geum japonicum may have potential use as new anti-hypertensive agents for lowering arterial blood pressure in hypertensive patients.