Analysis of the mechanisms underlying the vasorelaxant action of coptisine in rat aortic rings

The aim of the present study was to evaluate the vasorelaxant effects of coptisine and its possible mechanisms in isolated rat aortic rings. Coptisine was evaluated on isolated rat aortic rings precontracted with norepinephrine (NE) and KCl. The mechanisms were evaluated in the presence or absence of specific pharmacological inhibitors. Coptisine (1 ~ 200 μM) relaxed NE (1 μM) or KCl (60 mM) induced sustained contraction with pEC(50) values of 4.49 ± 0.48 and 4.85 ± 0.57 in a concentration dependent manner. Pretreatment with coptisine (10, 50 or 100 μM) also inhibited concentration-response curves to NE and KCl. The vasorelaxant effect of coptisine was attenuated significantly by endothelium removal, and incubation with Nω-nitro-L-arginine methyl ester (L-NAME, 100 μM), methylene blue (10 μM) and indomethacin (5 μM) partially reduced the vasorelaxant effect of coptisine. In endothelium-denuded rings, the vasorelaxant effect of coptisine was reduced significantly by 4-aminopyridine (4-AP, 100 μM), but not glibenclamide (10 μM) ortetraethylammonium (TEA, 5 mM). Coptisine also reduced NE-induced transient contraction in Ca(2+)-free solution, and inhibited contraction induced by increasing external calcium in Ca(2+)-free medium plus 60 mM KCl. It was concluded that coptisine induced both endothelium-dependent and -independent relaxation in rat aortic rings. The NO-cGMP mediated pathway may be involved in the endothelium-dependent relaxation and in the activation of voltage-dependent K(+) channels, contributing in part to the endothelium-independent relaxation bycoptisine. Coptisine also blocks extracellular Ca(2+) influx by interacting with both voltage- and receptor-operated Ca(2+) channels.     

Mechanisms underlying the vascular relaxation activities of Zingiber officinale var. rubrum in thoracic aorta of spontaneously hypertensive rats

ObjectiveTo evaluate vasorelaxant and vasoconstriction effects of Zingiber officinale var. rubrum (ZOVR) on live rats and isolated aortic rings of spontaneously hypertensive rats (SHRs).MethodsExtracts of ZOVR were subjected to in-vivo antihypertensive screening using noninvasive blood pressures in SHRs. The most potent extract, ZOVR petroleum ether extract (ZOP) was then fractionated using n-hexane, chloroform and water. Isolated thoracic aortic rings were harvested and subjected to vascular relaxation studies of n-hexane fraction of ZOP (HFZOP) with incubation of different antagonists such as N^ω-nitro-l-arginine methyl ester (L-NAME, 10 µmol/L), indomethacin (10 µmol/L), methylene blue (10 µmol/L), atropine (1 µmol/L), glibenclamide (10 µmol/L), prazosin (0.01 µmol/L), and propranolol (1 µmol/L).ResultsDuring the screening of various ZOVR extracts, ZOP produced the most reduction in blood pressures of SHRs and so did HFZOP. HFZOP significantly decreased phenylephrine-induced contraction and enhanced acetylcholine-induced relaxation. L-NAME, indomethacin, methylene blue, atropine, and glibenclamide significantly potentiated the vasorelaxant effects of HFZOP. Propranolol and prazosin did not alter the vasorelaxant effects of HFZOP. HFZOP significantly suppressed the Ca²⁺-dependent contraction and influenced the ratio of the responses to phenylephrine in Ca²⁺-free medium.ConclusionThis study demonstrates that ZOP may exert an antihypertensive effect in the SHR model. Its possible vascular relaxation mechanisms involve nitric oxide and prostacyclin release, activation of cGMP-K_ATP channels, stimulation of muscarinic receptors, and transmembrane calcium channel or Ca²⁺ release from intracellular stores. Possible active compounds that contribute to the vasorelaxant effects are 6-gingerol, 8-gingerol and 6-shogaol.     

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。     

Rhodiola‐Water Extract Induces β‐endorphin Secretion to Lower Blood Pressure in Spontaneously Hypertensive Rats

Rhodiola rosea (Rhodiola) is grown at high altitudes and northern latitudes. It is mainly used clinically as an adaptogen, but antihypertensive effects have been reported for the extract. These have not been well investigated, so in the present study, we evaluated the effect of Rhodiola‐water extract on blood pressure in spontaneously hypertensive rats (SHRs) and investigated the potential mechanism(s) for this action. In conscious male SHRs, systolic blood pressure (SBP) and heart rate were recorded using the tail‐cuff method. Plasma β‐endorphin was measured by enzyme‐linked immunosorbent assay. Rhodiola‐water extract decreased SBP in SHRs in a dose‐dependent manner, and this action was more significant than that in normal group named Wistar‐Kyoto (WKY) rats. This reduction of SBP in SHRs was inhibited by pretreatment with the selective opioid μ‐receptor antagonist, cyprodime, but not by naloxonazine, an antagonist specific to opioid μ1‐receptor. Also, the SBP‐lowering action of Rhodiola‐water extract was attenuated in adrenalectomized SHRs. Moreover, Rhodiola‐water extract dose‐dependently increased β‐endorphin release in SHRs, and the elevation of β‐endorphin in SHRs was higher than that in WKY. Thus, we suggest that Rhodiola‐water extract can induce release of β‐endorphin to lower SBP in SHRs. Copyright © 2012 John Wiley & Sons, Ltd.     

Antihypertensive and vasodilator effects of methanolic and aqueous extracts of Tribulus terrestris in rats

The effects of methanolic and aqueous extracts of Tribulus terrestris on rat blood pressure (BP) and the perfused mesenteric vascular bed were investigated. The extracts dose-dependently reduced BP in spontaneously hypertensive rats (SHRs) with the aqueous fraction being more potent than the methanolic fraction at all doses tested. In vitro, the methanolic but not aqueous extract produced a dose-dependent increase in perfusion pressure of the mesenteric vascular bed. When perfusion pressure was raised with phenylephrine (10(-5) M), the aqueous extract produced a dose-dependent reduction in perfusion pressure at all doses. A low dose of the methanolic extract produced a vasoconstrictor effect while higher doses produced dose-dependent reduction in perfusion pressure. L-NAME (10(-4) M) significantly reduced but did not abolish vasodilation induced by the extracts. Vasodilator responses to aqueous and methanolic fractions were significantly reduced in preparations where perfusion pressure was raised with KCl (60 mM). A combination of KCl and L-NAME abolished the vasodilator responses induced by the extracts. It was concluded that methanolic and aqueous extracts of Tribulus terrestris possess significant antihypertensive activity in spontaneously hypertensive rats. The antihypertensive effects appeared to result from a direct arterial smooth muscle relaxation possibly involving nitric oxide release and membrane hyperpolarization.     

Anti-ischemic effect of Aurantii Fructus on contractile dysfunction of ischemic and reperfused rat heart

Aurantii Fructus (AF) is one of the most well-known traditional herbal medicines frequently used for the treatment of cardiovascular symptoms in Korea. The anti-ischemic effects of AF on ischemia-induced isolated rat heart were investigated through analyses of changes in perfusion pressure, aortic flow, coronary flow, and cardiac output. The subjects in this study were divided into two groups: an ischemia-induced group without any treatment, and an ischemia-induced group with AF treatment. There were no significant differences in perfusion pressure, aortic flow, coronary flow, and cardiac output between them before ischemia was induced. The supply of oxygen and buffer was stopped for 10 min to induce ischemia in isolated rat hearts, and AF was administered during ischemia induction. AF treatment significantly prevented decreases in perfusion pressure, aortic flow, coronary flow, and cardiac output under ischemic conditions (p < 0.01). These results suggest that AF has distinct anti-ischemic effects through recovery of contractile dysfunction in ischemic heart.     

Antihypertensive effect of an aqueous extract of Zygophyllum coccineum L. in rats

The effects of an aqueous extract of Zygophyllum coccineum L. on rat blood pressure (BP) and on the mesenteric vascular bed were investigated. The extract dose-dependently reduced BP and heart rate in normotensive and spontaneously hypertensive rats (SHRs). It also reduced BP in pithed SHRs. In vitro, the extract had no effect on basal perfusion pressure of the mesenteric vascular bed. When the perfusion pressure was raised with noradrenaline or potassium chloride, the extract produced a dose-dependent reduction in perfusion pressure. However, in preparations in which the perfusion pressure was raised with KCl, the depressor response to lower doses of the extract was abolished while higher doses produced responses that were reduced in magnitude when compared with similar responses in preparations in which the perfusion pressure was raised with noradrenaline. It was concluded that extracts of Z. coccineum possess significant antihypertensive activity that may involve some membrane hyperpolarization.     

Effects of electroacupuncture at Taichong(LR 3) and Baihui(DU 20)on cardiac hypertrophy in rats with spontaneous hypertension

OBJECTIVE: To investigate the effects of electroacupuncture(EA) at Taichong(LR 3) and Baihui(DU 20)on myocardial hypertrophy in spontaneously hypertensive rats(SHRs).METHODS: Thirty-six SHRs were randomly assigned to model, EA, and Losartan groups, with twelve rats per group. Twelve Wistar Kyoto rats were selected as the normal control group. Systolic blood pressure(SBP) and cardiac function were measured in all rats.Expression levels of factors associated with the phosphoinositide 3-kinase/protein kinase B/mammalian target of rapamycin(PI3K/Akt/mTOR) pathway were evaluated by Western blotting and real-time PCR.Pathological changes of the heart tissue were observed by hematoxylin-eosin staining.RESULTS: After treatment, enhanced SBP was significantly decreased in the EA and Losartan groups compared with the model group(P 0.01). Echocardiographic and morphological analyses revealed that enhanced end-diastolic interventricular septal thickness and left ventricular posterior wall thickness, as well as ratio of left ventricular weight to body weight were markedly diminished in the EA and Losartan groups(P 0.01 or P 0.05), while reduced left ventricular end-diastolic dimension and left ventricular ejection fraction were significantly ameliorated(P 0.01). Real-time PCR and western blotting analyses showed that the expression levels of PI3K,Akt, and mT OR in SHRs were significantly up-regulated by EA and Losartan(P 0.01), while the expression levels of PTEN and ANP were down-regulated(P 0.01).CONCLUSION: EA at Taichong(LR 3) and Baihui(DU20) inhibited the development of cardiac hypertrophy and improved the cardiac function in SHRs, possibly through regulation of the PI3K/Akt/mTOR signalling pathway.     

Vasorelaxant and antihypertensive effect of Cocos nucifera Linn. endocarp on isolated rat thoracic aorta and DOCA salt-induced hypertensive rats

Ethnopharmacological relevance

The fruits of Cocos nucifera Linn. (Arecaceae) have long been used in traditional medicine for the treatment of cardio-metabolic disorders.

Aim of the study

To evaluate the ethanolic extract of Cocos nucifera Linn. endocarp (CNE) for its vasorelaxant activity on isolated rat aortic rings and antihypertensive effects in deoxycorticosterone acetate (DOCA) salt-induced hypertensive rats.

Materials and methods

Cocos nucifera Linn. endocarp was extracted with ethanol and characterized by HPLC. CNE was examined for its in vitro vascular relaxant effects in isolated norepinephrine, phenylephrine or potassium chloride pre-contracted aortic rings (both intact endothelium and denuded). In vivo anti-hypertensive studies were conducted in DOCA salt-induced uninephrectomized male Wistar rats.

Results

Removal of endothelium or pretreatment of aortic rings (intact endothelium) with l-NNA (10 μM) or ODQ (10 μM) followed by addition of contractile agonists prior to CNE significantly blocked the CNE-induced relaxation. Indomethacin (10 μM) and atropine (1 μM) partially blocked the relaxation, whereas glibenclamide (10 μM) did not alter it. CNE significantly reduced the mean systolic blood pressure in DOCA salt-induced hypertensive rats (from 185.3 ± 4.7 mmHg to 145.6 ± 6.1 mmHg). The activities observed were supported by the polyphenols, viz. chlorogenic acid, vanillic acid and ferulic acid identified in the extract.

Conclusions

These findings reveal that the vasorelaxant and antihypertensive effects of CNE, through nitric oxide production in a concentration and endothelium-dependent manner, is due to direct activation of nitric oxide/guanylate cyclase pathway, stimulation of muscarinic receptors and/or via cyclooxygenase pathway.     

Synergistic vasorelaxant and antihypertensive effects of Ligusticum wallichii and Angelica gigas

Aim of the study

The synergistic vasorelaxant and antihypertensive effects of Ligusticum wallichii and Angelica gigas were examined in isolated rat aorta rings and spontaneously hypertensive rats (SHRs).

Materials and methods

The ethanol extract of Ligusticum wallichii (LwEx) or Angelica gigas (AgEx) or their combinations at ratios Ligusticum wallichii:Angelica gigas = 1:1 (MxEx11), 1:3 (MxEx13), and 3:1 (and MxEx31), and their successive water soluble (LwDw, AgDw, MxDw11, MxDw13 and MxDw31) or n-butanol soluble fractions (LwBt, AgBt, MxBt11, MxBt13, and MxBt31) were examined for their vasorelaxant effects. In an antihypertensive study, LwEx, AgEx, or MxEx11 (100 mg/kg) was orally administered to SHRs, and the systolic, diastolic, and mean blood pressure were measured using the tail-cuff method before and 1, 3, 5, 7, and 24 h after oral administration.

Results

Each of the ethanol extracts caused long-term relaxation in endothelium-intact or endothelium-denuded rat aorta preconstricted with norepinephrine (NE, 300 nM). All of the water phases of the ethanol extracts elicited an endothelium-dependent acute relaxation, and the water phase of MxDw11 (EC₅₀ values: 1.08 mg/mL, P < 0.05) had the highest activity. MxDw11-induced acute relaxation was abolished by pretreatment with N^G-nitro-l-arginine (10 μM), methylene blue (1.0 μM), or atropine (0.1 μM), indicating that the response to MxDw involves the enhancement of the nitric oxide-cGMP system. On the other hand, all of the butanol phases showed an endothelium-independent long-term relaxation, and MxBt11 (85 ± 7% relaxation of NE-preconstricted active tone at 20 min after the addition, P < 0.05) displayed the highest activity. MxBt11-induced gradual relaxation was significantly attenuated by an inward rectifier potassium-channel inhibitor, but not by an ATP-sensitive or a large conductance Ca²⁺-activated potassium-channel blocker. Calcium concentration-dependent contraction curves in high-potassium, depolarizing medium were shifted significantly to the right and downward after incubation with MxBt11 (0.03, 0.1, and 0.3 mg/mL), implying that MxBt11 is also involved in the inhibition of extracellular calcium influx to vascular smooth muscle. MxEx11 (100 mg/kg) significantly reduced systolic blood pressure of SHRs at 3, 5, and 7 h after oral administration, but this effect was not induced by Ligusticum wallichii or Angelica gigas alone.

Conclusions

The combination of Ligusticum wallichii and Angelica gigas elicits a synergistic effect on vasorelaxation in isolated rat aortas and antihypertension in SHRs. The ratio of Ligusticum wallichii:Angelica gigas = 1:1 was the most effective of all combinations tested.     

Hypotensive and vasorelaxant effects of the procyanidin fraction from Guazuma ulmifolia bark in normotensive and hypertensive rats

THE AIM OF THE STUDY: was to investigate the in vivo and in vitro cardiovascular activity of a procyanidin fraction (PCF) obtained from acetone extract of Guazuma ulmifolia bark which has traditionally been used as an antihypertensive agent. RESULTS: 10 mg/kg PCF doses orally administered to sugar-fed hypertensive rats decreased both the systolic arterial pressure and the heart rate, whereas the same doses intravenously administered induced arterial hypotension which was attenuated by NG-nitro-L-arginine methylester (L-NAME 31 mg/kg) pretreatment. In these experiments we employed carbachol as a positive control test. The PCF reduced the contraction induced by norepinephrine (1x10(-7) M) in isolated aortic rings of normotensive (IC50=35.3+/-12.4 ng/mL) and sugar-fed hypertensive (IC50=101.3+/-57.2 ng/mL) rats. This relaxant activity was inhibited by either vascular endothelium removal or L-NAME (30 microM) pretreatment, while indomethacin (10 microM) or atropine (10 microM) had no effect. Preliminary analysis of the PCF by HPLC-DAD-MS and FAB+ mass spectrometry allowed the detection of the main components such as the complex of procyanidin oligomers consisting mainly of tetramers and trimers. CONCLUSIONS: Guazuma ulmifolia bark possesses long-lasting antihypertensive and vasorelaxing properties linked to the endothelium related factors, where nitric oxide is involved.     

Vascular effects and antioxidant activity of two Combretum species from Democratic Republic of Congo

Ethnopharmacological relevance

Combretum racemosum P. Beauv (Combretaceae) leaves (CrLv) and root bark (CrRB) and Combretum celastroides subsp. laxiflorum Welw (Combretaceae) leaves (ClLv) are used in Congolese traditional medicine for several therapeutic purposes, notably for the treatment of conditions consistent with hypertension. The present study aims to investigate the vasorelaxant and in vitro antioxidant activities of these plants polar extracts and to examine the in vivo antihypertensive effect of the extract which displays the most potent vasorelaxant effect.

Material and methods

The vasorelaxant effect of CrLv, CrRB and ClLv methanolic extracts was studied on rat aorta rings pre-contracted with phenylephrine (PE, 1 μM) in the presence or absence of the endothelium. In some experiments, prior to the addition of the extract, rings were incubated for 30 min with either L-N^G-nitroarginine methyl ester (L-NAME; 100 μM), a nitric oxide synthase (NOS) inhibitor, indomethacin (10 μM), a cyclooxygenase inhibitor, or 1 H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; 10 μM), a guanylate cyclase inhibitor. The antioxidant activity was determined by the measurement of the scavenging ability of extracts towards the stable free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH). Blood pressure was measured on normotensive Wistar rats and spontaneously hypertensive rats (SHR) treated orally with a daily dose (40 mg/kg) of the CILv extract for 5 weeks. Tested extracts have been characterised by TLC profiles targeted at flavonoids.

Results

All tested extracts showed an important DPPH scavenging activity, ranging from 0.6 to 1.1 quercetin-equivalents. They caused a concentration-dependent vasorelaxation on intact aortic rings pre-contracted with PE (1 μM). The responses to CrRB and CrLv methanolic extracts reached 74.0±5.1% and 62.2±8.6% at a cumulative concentration of 50 μg/ml, respectively. The ClLv (10 μg/ml) extract was more active and, in the same conditions, relaxed aortic rings by 90.3±5.8%. The vasorelaxant activity of all extracts disappeared or was significantly attenuated by removal of the endothelium or after pretreatment with L-NAME or ODQ. Indomethacin only inhibited the activity of CrLv and CrRB extracts. The ClLv extract was able to lower the systolic blood pressure in SHR rats by 7% after a 5-week treatment.

Conclusions

The present study shows that methanolic extracts from ClLv, CrRB and CrLv have an antioxidant activity and an endothelium-dependent vasorelaxant effect. ClLv induces the vasorelaxant effect through the NO-cGMP pathway while CrLv and CrRB extracts also act via a prostanoid pathway. ClLv extract demonstrated a modest but significant antihypertensive activity in SHR rats.     

舒脑欣滴丸对自发性高血压大鼠降压及心肌保护作用研究

目的观察舒脑欣滴丸对自发性高血压(SHR)大鼠的降压及心肌保护作用。方法将SHR大鼠按血压和体质量随机分为模型组、舒脑欣滴丸(800 mg/kg)组和阳性药缬沙坦(1 mg/kg)组。以同龄同种系正常血压的京都种(WKY)大鼠作为对照组,各组ig给药,采用无创血压计测定其血压,给药6周后测定大鼠血清中一氧化氮合酶(NOS)和血管紧张素Ⅱ(AngⅡ)的水平,并利用多普勒超声心动检查方法测定左心室质量,利用HE染色观察主动脉和心肌组织形态变化。结果舒脑欣滴丸(800mg/kg)单次给药后,SHR大鼠血压在1h后降到最低,长期给药6周后,可以稳定SHR大鼠的血压;舒脑欣滴丸治疗6周后,大鼠血清中NOS水平显著高于模型组(P0.05),AngⅡ水平显著低于模型组(P0.05),舒脑欣滴丸给药组的左心室质量显著低于模型组(P0.05),且舒脑欣滴丸可改善高血压引起的胸主动脉血管和心肌形态异常。结论舒脑欣滴丸对高血压伴有心肌肥厚大鼠具有一定治疗作用,可作为高血压伴心肌肥厚病症的潜在药物进行研究。     

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.     

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.     

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.     

The antihypertensive and vasodilator effects of aqueous extract from Berberis vulgaris fruit on hypertensive rats

The aqueous extract from Berberis vulgaris fruit (B.V.) was tested to evaluate its antihypertensive effects on DOCA-induced hypertension in the rats. Hypertension was induced in male Sprague-Dawley rats (200-250 g) by DOCA-salt injection (20 mg/kg, twice weekly, for 5 weeks, s.c.) plus NaCl (1%) which was added to the animals' drinking water. Then 5 weeks later, the rats were anaesthetized with thiopental (30 mg/kg, i.p.) and the arterial blood pressure was measured. The mean arterial blood pressure and heart rate were 231 +/- 6.4 (mmHg) and 506 +/- 12 (beats/min), respectively. Administration of B.V. extracts significantly reduced the rat arterial blood pressure. In in vitro studies, rings of descending aorta were cut and mounted for isometric tension recording in an organ chamber containing Krebs solution. Mesenteric beds were also removed and perfused with Krebs solution. After 1 h of stabilization, preparations (aortic rings or mesenteric beds) were precontracted with phenylephrine (10(-5) M), then different concentrations of B.V. (0.4, 2 and 4 mg/mL) were added which caused a relaxation in these vessels. To investigate the mechanism of action of the extract, the tissues were incubated with either L-NAME (10(-5) M) or indomethacin (10(-5) M) for 20 min. In the aortic rings L-NAME pretreatment could only reduce the vasodilatory effects of a low concentration of B.V. (0.4 mg/mL), but indomethacin was without effect. In isolated perfused mesenteric beds preincubation with either L-NAME or indomethacin did not modify the vasodilator effects of the aqueous extract from B.V. fruit. The present results suggest that the antihypertensive and vasodilatory effects of B.V. fruit extract are mainly endothelial-independent and it may be used to treat hypertension, a status with endothelial dysfunction.     

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.     

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.     

Vasorelaxant and antihypertensive effects of methanolic extracts from Hymenocardia acida Tul

Ethnopharmacological relevance

In Congolese traditional medicine, decoctions of Hymenocardia acida root bark (HaRB) and trunk bark (HaTrB) are used for the treatment of conditions assumed to be hypertension. In this work, we propose to study the vasorelaxant effect of HaRB and HaTrB methanolic extracts on isolated rat thoracic aorta, to characterize the group of molecules responsible for the observed vasorelaxant activity, to evaluate the in vitro antioxidant activity of these extracts and to determine the antihypertensive activity of the HaRB extract on spontaneously hypertensive rats (SHR).

Materials and methods

The vasorelaxant effect of the HaRB and HaTrB methanolic extracts was studied on endothelium-intact aortic rings pre-contracted with phenylephrine (PE, 1 μM). The mechanism of this vasorelaxant effect was investigated on endothelium-denuded vessels and on endothelium-intact aortic rings in the presence of three inhibitors: l-N^G-nitroarginine methyl ester (100 μM), indomethacin (10 μM) and 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (10 μM). To determine the nature of the compounds responsible for the vasorelaxant activity, we carried out a fractionation of the extracts and a thiolysis of the most active fraction followed by a liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS) analysis. The extracts antioxidant activity was determined by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) colorimetric assay. In vivo anti-hypertensive activity of the HaRB extract was conducted on SHR.

Results

HaRB and HaTrB methanolic extracts produced a concentration-dependent vasorelaxation on intact aortic rings pre-contracted with PE (1 μM). The vasorelaxant responses obtained were 95.3±1.5% (5 μg/ml) and 100.6±3.0% (1 μg/ml), respectively. The effect was markedly attenuated by removal of endothelium or pretreatment of aortic rings with all inhibitors except indomethacin. The LC/ESI-MS analysis of the thiolysis products indicated that the fraction which caused the most important vasorelaxation (97.9±2.5% at 3 μg/ml) was a mixture of procyanidins and prodelphinidins, with a predominance of procyanidins. Both extracts and all fractions from HaRB extract showed a DPPH scavenging activity, ranging from 0.4 to 0.8 quercetin-equivalents. The HaRB methanolic extract reduced the systolic blood pressure in SHR (from 214±3 mmHg to 194±4 mmHg) after a 5-week treatment.

Conclusions

The methanolic extracts of Hymenocardia acida root and trunk bark have vasorelaxant activity. The vasorelaxant effect observed is endothelium-dependent and seems mainly mediated through the NO-cGMP pathway. The COX pathway is not involved. The vasorelaxant activity appears to be due to polymeric procyanidins and prodelphinidins. These extracts also have an antioxidant effect. The extract of Hymenocardia acida root bark shows a significant but weak antihypertensive activity in SHR.