Endothelium-denuded Aorta Rings Research Articles

PS-BPB03-2: VASORELAXANT-MEDIATED ANTIHYPERTENSIVE EFFECT OF THE SEED AQUEOUS EXTRACT OF AFRAMOMUM PRUINOSUM GAGNEP. (ZINGIBERACEAE)

Objective: Despite the existing therapies, arterial hypertension is still a prevalent and a worldwide major public health concern, prompting the search for new therapeutic alternatives. The present study investigated the antihypertensive and the related mechanisms of action of the seed aqueous extract of Aframomum pruinosum (AEAP), a plant used in Cameroon traditional medicine against cardiovascular ailments. Design and method: Male Wistar rats were rendered hypertensive by chronic oral administration of L-NAME (30 mg/kg/day) for three consecutive weeks, and hypertensive rats were selected and treated with L-NAME alone or in combination with AEAP at doses of 75 or 150 mg/kg/day for an additional 3 consecutive weeks. Captopril (25 mg/kg/day, p.o) was used as reference drug. Blood pressure and heart rate were monitored weekly. At the end of the experiment, the heart was harvested, weighed, and sections of cardiac tissue were stained with hematoxylin and eosin for histological analysis. Cumulative concentrations of the aqueous extract (3, 10, 30, 100, and 300 μg/mL) were tested on intact or endothelium-denuded aorta rings precontracted with norepinephrine (NE; 1 μM) or KCl (90 mM) in absence or presence of L-NAME (a nitric oxide synthase inhibitor, 100 μM), indomethacin (a prostaglandin synthesis inhibitor; 10 μM), methylene blue (a guanylate cyclase inhibitor, 1 μM), tetraethylammonium (TEA; a non-specific potassium channel blocker; 5 μM) or glibenclamide (an ATP-sensitive potassium channel blocker; 10 μM). The contractile response to NE, or CaCl2 was also assessed in the presence or absence of the plant extract. Results: AEAP completely reversed (p < 0.001) L-NAME-induced elevated systolic and diastolic blood pressure, and increased heart rate. AEAP partially reversed cardiac hypertrophy, leucocyte infiltration, and prevent cardiac necrosis. AEAP induced a concentration-dependent vasorelaxant effect on NE- and KCl-evoked contraction with EC50 values of 13.46 and 49.37 μg/mL, respectively. Removal of the endothelium and the preincubation of aorta rings with L-NAME significantly (p < 0.05) reduced the vasorelaxant effect of the plant extract, while indomethacin and methylene blue had no effect (p > 0.05). Glibenclamide, similar to TEA, significantly (p < 0.001) inhibited the vasorelaxant response to AEAP. Also, the extract significantly (p < 0.01 and p < 0.001) inhibited NE- and CaCl2-induced contraction. Conclusion: AEAP possesses antihypertensive effects that are at least partially mediated by its vasorelaxant activity. Nitric oxide release, opening of KATP channels, blockade of alpha-1 receptors, and inhibition of Ca2+ influx account for this vasorelaxant activity.

Blood pressure lowering effect and vascular activity of Phyllanthus niruri extract: The role of NO/cGMP signaling pathway and β-adrenoceptor mediated relaxation of isolated aortic rings.

Phyllanthus niruri have a long history of use in the traditional treatment of various ailments including hypertension. Literature reports have indicated that it is a potent antihypertensive herbal medication used traditionally. This study was carried out to investigate the antihypertensive and vasodilatory activity of four solvents extracts of P. niruri namely; petroleum ether (PEPN), chloroform (CLPN), methanol (MEPN) and water (WEPN), with the aim of elucidating the mechanism of action and identifying the phytochemical constituents. Male Spontaneous Hypertensive Rats (SHRs) were given oral gavage of P. niruri extract daily for two weeks and the blood pressure was recorded in vivo. We also determine the vasodilation effect of the extracts on rings of isolated thoracic aorta pre-contracted with phenylephrine (PE, 1μM). Endothelium-intact or endothelium-denuded aorta rings were pre-incubated with various antagonists like 1H-[1,2,4] oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ, 10μM) and Methylene blue (MB 10μM), sGC inhibitors; Nω-Nitro-L-arginine methyl ester hydrochloride (L-NAME, 10μM) a nitric oxide synthase (NOS) inhibitor; atropine (10μM), a cholinergic receptor blocker; indomethacin (10μM), a cyclooxygenase inhibitor and various K+ channel blockers such as glibenclamide (10μM) and tetraethyl ammonium (TEA 10μM) for mechanism study. SHRs receiving P. niruri extracts showed a significant decrease in their blood pressure (BP) when compared to the baseline value, with PEPN being more potent. The extracts (0.125-4mg/mL) also induced vasorelaxation on endothelium-intact aorta rings. PEPN elicited the most potent maximum relaxation effect (Rmax). Mechanism assessment of PEPN showed that its relaxation effect is significantly suppressed in endothelium-denuded aorta rings. Pre-incubation of aorta rings with atropine, L-NAME, ODQ, indomethacin, and propranolol also significantly attenuated its relaxation effect. Conversely, incubation with TEA and glibenclamide did not show a significant effect on PEPN-induced relaxation. This study indicates that the antihypertensive activity of P. niruri extract is mediated by vasoactive phytoconstituents that dilate the arterial wall via endothelium-dependent pathways and β-adrenoceptor activity which, in turn, cause vasorelaxation and reduce blood pressure.

Low molecular weight fucoidan ameliorates streptozotocin-induced hyper-responsiveness of aortic smooth muscles in type 1 diabetes rats

Ethnopharmacological relevanceLow molecular weight fucoidan (LMWF) was prepared from Laminaria japonica Areschoug, a popular seafood and medicinal plant consumed in Asia. Chinese have long been using it as a traditional medicine for curing hypertension and edema. Aim of the studyThis study was intent to investigate the possible beneficial effect of LMWF on hyper-responsiveness of aortic smooth muscles instreptozotocin (STZ)-induced type 1 diabetic rats. Materials and methodsSprague-Dawley rats were made diabetic by injection of STZ, followed by the administration of LMWF (50 or 100mg/kg/day) or probucol (100mg/kg/day) for 12 weeks. Body weight, blood glucose level, basal blood pressure, serum lipid profiles, oxidative stress, prostanoids production, and vasoconstriction response of endothelium-denuded aorta rings to phenylephrine were measured by Real time-PCR, Western blots, ELISA assay, and force myograph, respectively. ResultsLMWF (100mg/kg/day)-treated group showed robust improvements on STZ-induced body weight-loss, hypertension, and hyperlipidaemia as indicated by decreased serum level of total cholesterol, triglyceride, and low density lipoprotein cholesterol; while probucol, a lipid-modifying drug with antioxidant properties, displayed mild effects. In addition, LMWF appreciably ameliorated STZ-elicited hyper-responsiveness and oxidative stress in aortic smooth muscles as indicated by decreased superoxide level, increased glutathione content and higher superoxide dismutase activity. Furthermore, administration with LMWF dramatically prevented cyclooxygenase-2 stimulation and restored the up-regulation of thromboxane synthase and down-regulation of 6-keto-PGF1α (a stable metabolic product of prostaglandin I2) in the STZ-administered rats. ConclusionThis study demonstrates for the first time that LMWF can protect against hyperlipidaemia, hypertension, and hyper-responsiveness of aortic smooth muscles in type 1 diabetic rat via, at least in part, amelioration of oxidative stress and restoration of prostanoids levels in aortic smooth muscles. Therefore, LMWF can be a potential adjuvant treatment against cardiovascular complications in type 1 diabetes.

Vasorelaxation effect of gastrodin on isolated thoracic aorta rings of rats

To study the effect of gastrodin on isolated thoracic aorta rings of rats and to investigate the potential mechanism. A perfusion model of isolated thoracic aorta rings of rats was applied. The effect of cumulative gastrodin (5, 50, 100,150, 200, and 250 μmol/L) on endothelium-intact aorta rings was investigated. The same procedure was applied to observe the effect of gastrodin on endothelium-intact/denuded aorta rings pre-contracted with 10(-6) mol/L phenylephrine hydrochloride (PE). The aorta rings incubated by 200 mmol/L gastrodin in the Ca(2+)-free (K-H) solution was contracted by using PE. The effect of 200 mmol/L gastrodin on endothelium-denuded aorta rings pre-contracted with 60 mmol/L KCl was also observed. Compared with the denuded gastrodin group, the intact gastrodin group could significantly relax the PE-contracted aorta rings (P<0.01). In Ca(2+)-free (K-H) solution KHS, the PE-induced contraction rate of aorta rings pre-incubated by gastrodin was 6.5%±0.7%, which was significantly less than the control group (11.8%±0.9%,P<0.01). However, after 3 mmol/L CaCl2 was added, the Ca(2+)-induced contraction in the gastrodin group (51.7%±2.4%) was similar to that in the control group (49.8%±2.8%). The contractile rate of rings in the KCl-contracted gastrodin group (96.3%±0.6%) was not significantly different from that in the control group (96.8%±1.2%). Gastrodin has the effect of vasorelaxation on isolated thoracic aorta rings of rats. The mechanism of the vasorelaxation of gastrodin may mainly work through the inhibition of inositol 1, 4, 5-trisphosphosphate receptor on the sarcoplasmic reticulum of the arterial smooth muscle, which leads to the reduction of the Ca(2+) released from the sarcoplasmic reticulum.

Mechanisms of the dilator action of the Erigerontis Herba on rat aorta

Ethnopharmacological relevanceErigerontis Herba is widely used as a traditional Chinese medicine and is commonly used for neuroprotection and vascular protection. Aim of studyIn this study, the vasodilator effects of Erigerontis Herba (DZXX) were investigated using rat isolated aorta rings. Material and methodThe involvement of endothelium in the vasorelaxation was studied by comparing response of endothelium-intact and endothelium-denuded aorta rings which precontracted with U46619. The involvement of K+ channels was studied by pretreatment of the aorta rings with various K+ channel inhibitors. The involvement of Ca2+ channel was studied by incubating aorta rings with Ca2+-free solution, primed with U46619 prior to elicit contraction by addition of Ca2+ solution. ResultsDZXX (0.2–2mg/ml) induced a concentration-dependent relaxation on U44619-precontracted aorta rings with EC50 of 0.354±0.036mg/ml. Removal of endothelium or pretreatment with a BKCa inhibitor iberiotoxin, KIR inhibitor barium chloride or Kv inhibitor 4-aminopyridine produced no effect on the DZXX-induced vasorelaxation. However, pretreatment with a KATP inhibitor glibenclamide or a non-selective K+ channel inhibitor tetraethylammonium produced significant inhibition on the DZXX-induced vasorelaxation by 29.9% and 21.3%, respectively. Pretreatment with DZXX (0.4, 1.2 and 2mg/ml) produced a concentration-dependent inhibition on Ca2+-induced vasoconstriction. ConclusionsThese results suggest that the vasodilator effect of DZXX was endothelium-independent, mediated by decreasing the influx of Ca2+ by calcium channel inhibition and increasing the influx of K+ by opening of a KATP channel.

Involvement of nitric oxide and prostacyclin in the antihypertensive effect of low-molecular-weight procyanidin rich grape seed extract in male spontaneously hypertensive rats

The aim of this study was to evaluate the involvement of endothelial-relaxing factors as possible antihypertensive mechanism of low-molecular-weight procyanidin rich grape seed extract (LM-GSPE). Thirty 17–20-week-old male spontaneously hypertensive rats (SHR) were administered water or 375mg/kg LM-GSPE by intragastric gavage. One millilitre of saline, 30mg/kg NG-Nitro-l-arginine methyl ester (l-NAME) or 5mg/kg indomethacin was administrated intraperitoneally. Systolic blood pressure (SBP) and diastolic blood pressure (DBP) were recorded before and 6h after oral administration. Plasma concentration of 6-keto-prostaglandin F1α (PGF1α) was quantified. In addition, we evaluated the relaxation caused by LM-GSPE in different aorta preparations. The antihypertensive effect of LM-GSPE was completely and partially abolished by l-NAME and indomethacin, respectively. In addition, plasma PGF1α was increased in LM-GSPE-administered rats. Finally, LM-GSPE relaxed the intact aorta preparations but did not relax the endothelium-denuded aorta rings. l-NAME inhibited the relaxation caused by LM-GSPE in the SHR aorta rings, but indomethacin did not. Therefore, the antihypertensive effect of LM-GSPE in SHR is endothelium dependent, and it could be mediated by changes in endothelium-derived nitric oxide bioavailability. Nevertheless, prostacyclin could also contribute additionally to this effect.

Nitric oxide mediates the antihypertensive and vascular relaxing effects of a soluble cocoa fiber product in spontaneously hypertensive rats

The involvement of endothelial-relaxing factors on the vascular and antihypertensive effects of a cocoa fiber product (CFP) obtained from cocoa husks was studied. We carried out in vitro experiments with aorta rings from untreated spontaneously hypertensive rats (SHR) and in vivo experiments with SHR. CFP did not relax the endothelium denuded aorta rings and NW-nitro-l-arginine methyl ester (l-NAME) partially blocked the vascular relaxing and antihypertensive effects of CFP. Nevertheless, indomethacin did not modify these effects. Nitric oxide mediates therefore the antihypertensive and aorta relaxing effects of CFP in SHR.

Vasodilator effect of oroxylin A on thoracic aorta isolated from rats

To investigate the vasodilator effect and the endothelium-dependent mechanism of oroxylin A in thoracic aorta isolated from rats. Thoracic aorta was isolated from Wistar rats. After pretreatment with norepinephrine or KCl, the effects of oroxylin A at different concentrations were detected on isolated vascular rings prepared from rats' thoracic aorta. The response of thoracic aortic ring was evaluated in the presence and absence of endothelium, and NG-nitro-L-arginine methyl ester (L-NAME), a specific inhibitor of nitric oxide synthase. Oroxylin A (10 and 100 μmol/L) caused vasodilation on endothelium-intact aortic rings pretreated with norepinephrine (1 μmol/L) and KCl (60 mmol/L) compared with the control (P<0.05, P<0.01). The vasodilation function of 10 and 100 μmol/L oroxylin A on the endothelium-denuded aorta rings was significantly lower than that on the endothelium-intact aorta rings (P<0.05, P<0.01). L-NAME pretreatment significantly attenuated the effect of 100 μmol/L oroxylin A on endothelium-intact aorta rings (P<0.05, P<0.01). Oroxylin A can induce the relaxation of the aorta ring in endothelium-dependent manner. Nitric oxide may be involved in the endothelium-dependent effect of oroxylin A.

Mechanisms for antihypertensive effect of CocoanOX, a polyphenol-rich cocoa powder, in spontaneously hypertensive rats

We investigate the mechanisms involved in the long-term antihypertensive effect of a polyphenol-rich cocoa powder, named CocoanOX® (CCX), in spontaneously hypertensive rats (SHR). We have carried out two different batches of experiments. For the first batch of experiments, forty 3week-old male SHR were randomly divided with ad libitum intake into four groups of 10 animals, that respectively received the following drinking fluids up to the 20th week of life (treatment period): tap water (control), CCX 100mg/kg/day, CCX 200mg/kg/day and CCX 400mg/kg/day. Five 20week-old rats of each group were sacrificed by decapitation. From the 20th to 24th week of life all the remaining animals were given tap water (follow-up period), and all of them were sacrificed at the end of the follow-up period. Plasma malondialdehyde (MDA), reduced glutathione in the liver, plasma and aorta angiotensin converting enzyme (ACE) activity and plasma angiotensin II were determined in all the sacrificed SHR that were included in this batch of experiments. Plasma MDA decreased and liver reduced glutathione increased in the 20week-old CCX treated SHR. These effects were not observed in the rats that were sacrificed after the follow-up period. CCX treatment did not modify aorta ACE activity, but the activity of ACE and the levels of angiotensin II increased in the plasma of the SHR treated with the highest dose of CCX. ACE activity returned to basal values in the SHR that were sacrificed after the follow-up period. However, angiotensin II levels were slightly higher after withdrawal of CCX.For the second batch of experiments we used aorta rings obtained from untreated SHR, and we evaluated the relaxation caused by CCX in different aorta preparations. CCX relaxed the intact aorta preparations but this cocoa did not relax the endothelium-denuded aorta rings from the untreated SHR. l-NAME, but not indomethacin, inhibited the relaxation caused by CCX in the SHR aorta rings. We postulate that the antihypertensive effect of CCX might be mediated by an improvement of endothelial release of nitric oxide and by a reduction of oxidative stress. The inhibition of ACE could be implicated in the antihypertensive effect of CCX.

Alpha-2 adrenoceptors are present in rat aorta smooth muscle cells, and their action is mediated by ATP-sensitive K(+) channels.

The role of alpha(2)-adrenoceptors in the response of aorta smooth muscle rings to the alpha(2)-adrenoceptors agonists UK 14,304 and clonidine was studied. Stimulation by 1 - 10 nM UK 14,304 caused dose-dependent relaxant responses in BaCl(2)-contracted endothelium-denuded aorta rings, and hyperpolarization in rings with or without endothelium, which were inhibited by yohimbine and glibenclamide, but not affected by prazosin, propranolol, apamin or iberiotoxin. At higher concentrations (10 nM - 10 microM) UK 14,304 also induced a depolarizing effect which was potentiated by yohimbine and inhibited by prazosin. These results indicate that UK 14,304 acts on alpha(2)-adrenoceptors at lower concentrations and on both alpha(1)- and alpha(2)-adrenoceptors above 10 nM. In rings, with or without endothelium, noradrenaline had a depolarizing effect which was inhibited by prazosin. Adrenaline did not affect the membrane potential but in the presence of prazosin caused hyperpolarization, which was inhibited by yohimbine and glibenclamide. These results indicate that noradrenaline is more selective for alpha(1)-, whereas adrenaline has similar affinities for alpha(1)- and alpha(2)-adrenoceptors. In aortae with endothelium, L-NNA caused a small depolarization but did not affect the hyperpolarization induced by UK 14,304, indicating that NO is not involved in that response. Glibenclamide induced a small depolarization in aortae, with or without endothelium, indicating that ATP-sensitive K(+) channels may play a role in maintaining the smooth muscle's membrane potential. Our results indicate that, in rat aorta, alpha(2)-adrenoceptors are also present in the smooth muscle, and that these receptors act through small-conductance ATP-sensitive K(+) channels.