Endothelium-intact Aorta Research Articles

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.

Mepivacaine-induced contraction is attenuated by endothelial nitric oxide release in isolated rat aorta

Mepivacaine is an aminoamide-linked local anesthetic with an intermediate duration that intrinsically produces vasoconstriction both in vivo and in vitro. The aims of this in-vitro study were to examine the direct effect of mepivacaine in isolated rat aortic rings and to determine the associated cellular mechanism with a particular focus on endothelium-derived vasodilators, which modulate vascular tone. In the aortic rings with or without endothelium, cumulative mepivacaine concentration-response curves were generated in the presence or absence of the following antagonists: N(ω)-nitro-L-arginine methyl ester [L-NAME], indomethacin, fluconazole, methylene blue, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one [ODQ], verapamil, and calcium-free Krebs solution. Mepivacaine produced vasoconstriction at low concentrations (1 × 10(-3) and 3 × 10(-3) mol/L) followed by vasodilation at a high concentration (1 × 10(-2) mol/L). The mepivacaine-induced contraction was higher in endothelium-denuded aortae than in endothelium-intact aortae. Pretreatment with L-NAME, ODQ, and methylene blue enhanced mepivacaine-induced contraction in the endothelium-intact rings, whereas fluconazole had no effect. Indomethacin slightly attenuated mepivacaine-induced contraction, whereas verapamil and calcium-free Krebs solution more strongly attenuated this contraction. The vasoconstriction induced by mepivacaine is attenuated mainly by the endothelial nitric oxide - cyclic guanosine monophosphate pathway. In addition, mepivacaine-induced contraction involves cyclooxygenase pathway activation and extracellular calcium influx via voltage-operated calcium channels.

The Vasorelaxant Mechanisms of a Rho Kinase Inhibitor DL0805 in Rat Thoracic Aorta

Rho-kinase has been suggested as a potential therapeutic target in the treatment of cardiovascular diseases. The Rho-kinase signaling pathway is substantially involved in vascular contraction. The aim of the present study was to evaluate the vasorelaxant effects of Rho kinase inhibitor DL0805 in isolated rat aortic rings and to investigate its possible mechanism(s). It was found that DL0805 exerted vasorelaxation in a dose-dependent manner in NE or KCl-induced sustained contraction and partial loss of the vasorelaxation under endothelium-denuded rings. The DL0805-induced vasorelaxation was significantly reduced by the nitric oxide synthase inhibitor Nω-nitro-L-arginine methyl ester, the guanylate cyclase inhibitor methylene blue and the cyclooxygenase inhibitor indomethacin. The voltage-dependent K+ channel blocker 4-aminopyridine remarkably attenuated DL0805-induced relaxations. However, the ATP-sensitive K+ channel blocker glibenclamide and Ca2+-activated K+ channel blocker tetraethylammonium did not affect the DL0805-induced relaxation. In the endothelium-denuded rings, DL0805 also reduced NE-induced transient contraction and inhibited contraction induced by increasing external calcium. These findings suggested that DL0805 is a novel vasorelaxant compound associated with inhibition of Rho/ROCK signaling pathway. The NO-cGMP pathway may be involved in the relaxation of DL0805 in endothelium-intact aorta. The vasorelaxant effect of DL0805 is partially mediated by the opening of the voltage-dependent K+ channels.

Vasorelaxant action of the total alkaloid fraction obtained from Solanum paludosum Moric. (Solanaceae) involves NO/cGMP/PKG pathway and potassium channels

Ethnopharmacological relevanceSolanum paludosum Moric. (jurubeba-roxa) is commonly used to treat hypertension as a substitute for Solanum paniculatum L. (jurubeba verdadeira). The total ethanolic extract from the root bark of Solanum paludosum have been found to cause hypotension in rats. Aim of the studyTo investigate the mechanism by which the total alkaloid fraction obtained from the root bark of Solanum paludosum (FAT-SP) acts as a vasorelaxant agent on rat thoracic aorta. Materials and methodsRings of rat aorta were suspended in organ bath containing Krebs solution at 37°C, bubbled with carbogen mixture (95% O2 and 5% CO2) under a resting tension of 1g. Isometric contractions were measured using a force transducer coupled to an amplifier and a microcomputer. ResultsFAT-SP has been found cause relaxation of the aortic rings pre-contracted with phenylephrine (Phe) in a concentration-dependent manner, in the presence and absence of endothelium. This effect was more potent on the endothelium-intact aorta. In the presence of endothelium, neither indomethacin (non-selective cyclooxygenase inhibitor) nor atropine (non-selective muscarinic receptor antagonist), produced significant changes on the relaxation response. On the other hand, in the presence of calmidazolium (a calmodulin inhibitor), N-nitro-l-arginine methyl ester (l-NAME, nitric oxide synthase inhibitor), hydroxocobalamin (HDX) (scavenger of free-radical nitric oxide), 1-H-[1,2,4]-oxadiazolo-[4,3a]-quinoxalin-1-one (ODQ, selective blocker of soluble guanylate cyclase), Rp-8-bromo-β-phenyl-1,N2-ethenoguanosine 3′:5′-cyclic monophosphorothioate sodium salt hydrate (Rp-8-Br-PET-cGMPS, competitive inhibitor of cGMP-dependent protein kinase G) or TEA+ (tetraethylammonium, nonselective potassium channel blocker), the vasorelaxant effect was significantly reduced, suggesting the involvement of NO/sCG/PKG pathway and potassium channel opening in vasorelaxant action of the FAT-SP. ConclusionThe mechanism of vasorelaxant activity of the FAT-SP on rat aorta involves both NO/sCG/PKG pathway and potassium channels.

Study on the application of intestinal absorption in vitro coupled with bioactivity assessment in Yuanhu Zhitong preparation

Generally, crude herbal extracts contain hundreds of components, and only the absorbed constituents among them may produce possible pharmacological effects. In previous studies, researchers directly utilized crude herbal extracts into cells or organs culture system for pharmacological test, which might easily result in false positive or false negative results. Therefore, reasonable pharmacological methods for investigation of crude herbal drugs in vitro were greatly needed. The objective of this research is to study the feasibility of combination of two simple biological methods, intestinal absorption test and vasorelaxation assay in the pharmacological research of Yuanhu Zhitong preparation (YZP). The intestinal absorption test was carried out to investigate the accounts of seventeen constituents in YZP and prepare the intestinal absorbed samples for vasorelaxation assay. The 17 absorbed constituents in three concentrations of YZP (0.16, 0.08, 0.04 g/ml) were detected by rapid resolution liquid chromatography coupled with a triple quadruple electrospray tandem mass spectrometry. The vasorelaxation of absorbed YZP solutions were determined by isolated aorta test and a mixture containing 7 main detected constituents was chosen for bioassay. The accounts of 17 constituents in YZP significantly varied. The good vasorelaxation of YZP was first found on the endothelium-intact aorta precontracted by KCl (60 mmol/L), with the relaxation rate of 81.53 ± 3.98, 66.85 ± 10.01 and 43.64 ± 17.83% at three different concentrations (0.16, 0.08 and 0.04 g/ml). However, the bioassay results of the mixture showed that it had lower bioactivity than that of the preparation. Based on adequate biopharmaceutical properties, the combinative methods may be more reasonable than conventional method in pharmacological research, and the intestinal absorption test coupled with vasorelaxation evaluation can be used together to investigate vasoactive effects of Traditional Chinese Medicine (TCM) in vitro. Key words: Intestinal absorption, vasorelaxation, Yuanhu Zhitong preparation, aortic rings, Traditional Chinese medicine.

Vasodilator Effect of Phlomis bracteosa Constituents Is Mediated through Dual Endothelium-Dependent and Endothelium-Independent Pathways

This study describes the vasorelaxant potential of some pure compounds isolated from Phlomis bracteosa L.: marrubiin, phlomeoic acid, and two new constituents labeled as RA and RB. In rat thoracic aortic rings denuded of endothelium, marrubiin, phlomeoic acid, RA, and RB caused relaxation of high K+ (80 mM) and phenylephrine (1 μM)-induced contractions at the concentration range of 1.0–1000 μg/mL. Marrubiin, phlomeoic acid, RA, and RB concentration dependently (3.0–10 μg/mL) shifted the Ca++ curves to the right obtained in Ca++-free medium. The vasodilator effect of marrubiin, phlomeoic acid, RA, and RB was partially blocked by Nω-nitro-L-arginine methyl ester in endothelium-intact aorta preparations. These results reveal that P. bracteosa constituents: marrubiin, phlomeoic acid, RA, and RB exhibit vasodilator action occurred via a combination of endothelium-independent Ca++ antagonism and endothelium-dependent Nω-nitro-L-arginine methyl ester-sensitive nitric oxide-modulating mechanism.

Effects of hawthorn leaf flavonoids on contraction and relaxation in isolated rat thoracic aortic rings

Objective To investigate the effects and mechanisms of hawthorn leaf flavonoids (HLF) on isolated thoracic aorta in rats. Methods The tension of rat thoracic aorta tings was measured.The effects of HLF on the thoracic aorta preconstricted by potassium chloride ( KCl, 6 × 10-2 mol/L) and norepinephrine (NE, 1 × 10-6 mol/L), as well as the effects of L-nitro arginine methyl ester (L-NAME,1 × 10-5 mol/L) and indomethacin ( 1 × 10-4 mol/L) on the relaxation response of HLF were observed.Results HLF completely relaxed the constriction induced by NE ( 1 × 10 -6 mol/L) in endothelium-intact thoracic aorta ( P ＜ 0. 01 ), but had no effect on those preconstricted aorta rings by a high concentration of KCl (6 × 10-2 mol/L) in endothelium-intact and endothelium-denuded rat aorta (P ＞ 0. 05). The relaxation response of HLF was significantly inhibited by L-NAME (P ＜ 0. 01 ), but not by indomethacin (P ＞0. 05). Conclusion The vasorelaxation induced by HLF in rat aorta rings may involve the reduction of Ca2+ influx through the calcium channels operated by receptor (ROC). The endothelium-dependent relaxation of HLF may be related to the generation of nitric oxide (NO). Key words: Hawthorn leaf flavonoids; Thoracic aorta rings; NO

Levobupivacaine-induced contraction of isolated rat aorta is calcium dependent

Levobupivacaine is a long-acting local anesthetic that intrinsically produces vasoconstriction in isolated vessels. The goals of this study were to investigate the calcium-dependent mechanism underlying levobupivacaine-induced contraction of isolated rat aorta in vitro and to elucidate the pathway responsible for the endothelium-dependent attenuation of levobupivacaine-induced contraction. Isolated rat aortic rings were suspended to record isometric tension. Cumulative levobupivacaine concentration-response curves were generated in either the presence or absence of the antagonists verapamil, nifedipine, SKF-96365, 2-aminoethoxydiphenylborate, Gd(3+), N(W)-nitro-l-arginine methyl ester (L-NAME), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), and methylene blue, either alone or in combination. Verapamil, nifedipine, SKF-96365, 2-aminoethoxydiphenylborate, low calcium concentrations, and calcium-free Krebs solution attenuated levobupivacaine-induced contraction. Gd(3+) had no effect on levobupivacaine-induced contraction. Levobupivacaine increased intracellular calcium levels in vascular smooth muscle cells. L-NAME, ODQ, and methylene blue increased levobupivacaine-induced contraction in endothelium-intact aorta. SKF-96365 attenuated calcium-induced contraction in a previously calcium-free isotonic depolarizing solution containing 100mmol/L KCl. Levobupivacaine-induced contraction of rat aortic smooth muscle is mediated primarily by calcium influx from the extracellular space mainly via voltage-operated calcium channels and, in part, by inositol 1,4,5-trisphosphate receptor-mediated release of calcium from the sarcoplasmic reticulum. The nitric oxide - cyclic guanosine monophosphate pathway is involved in the endothelium-dependent attenuation of levobupivacaine-induced contraction.

Identification of the Strong Vasorelaxing Substance Scirpusin B, a Dimer of Piceatannol, from Passion Fruit (Passiflora edulis) Seeds

Piceatannol is present in passion fruit (Passiflora edulis) seeds in high amounts. In this study, we isolated the second major polyphenolic compound of passion fruit seeds and identified it as scirpusin B, which is a dimer of piceatannol. We investigated the antioxidant activities and vasorelaxing effects of these polyphenols. Their antioxidant effects were measured using an in vitro 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay, and their vasorelaxant effects were determined ex vivo in rat thoracic aorta. Both polyphenolic compounds exhibited potent antioxidant activities and significant vasorelaxant effects in endothelium-intact aortas. More specifically, scirpusin B exerted a greater antioxidant activity and vasorelaxant effect compared with that of piceatannol. Additionally, the vasorelaxation effects of the compounds were induced via the NO derived from the endothelium. This study provides the possibility that polyphenols in passion fruit seeds are effective against cardiovascular diseases (CVDs).

Hypotensive effect of the water extract of the leaves of Pseuderanthemum palatiferum

The cardiovascular effects of the water extract from fresh leaves of P. palatiferum (PP) were evaluated in rats in both in vivo and in vitro models. The PP extract consisted of alkaloids, coumarins and sterols. The extract (5-25mg/kg, I.V.) decreased both the mean arterial blood pressure and heart rate of normotensive and L: -N-(ω)-nitro-arginine methyl ester (L: -NAME)-induced hypertensive anesthetized rats. The extract caused relaxation of the norepinephrine-contracted endothelium-intact aorta ring (EC(50)=81.0μg/mL). Functional removal of the endothelium attenuated the vasodilatation effect of the extract (EC(50)=136.4μg/mL). Pretreatment with L: -NAME or atropine did not alter the vasodilation effect of the extract. Pre-incubation with atropine did not alter bradycardic effect of the extract on isolated rat atrium. The effects of isoproterenol on isolated atrium were attenuated by the extract (2.5-5mg/mL). In conclusion, the water extract from fresh leaves of P. palatiferum possessed hypotensive and bradycardic effects. The vasorelaxant effect of the extract was dependent partly on the vascular endothelium but was not dependent on the synthesis of nitric oxide and did not act through activation of the muscarinic receptor.

Vasorelaxant and hypotensive effects of the extract and the isolated flavonoid rutin obtained from Polygala paniculata L.

This study aimed to investigate the in-vitro and in-vivo cardiovascular effects of the crude hydroalcoholic extract from Polygala paniculata (HEPP) in rats. The procedures were performed on aortic rings and on normotensive anaesthetized rats. When tested in endothelium-intact aorta rings, HEPP (30-1000 µg/ml) produced a significant non-concentration-dependent relaxing effect (∼40%), which was completely prevented by incubation with L-NAME (nitric oxide synthase inhibitor), ODQ (soluble guanylate cyclase inhibitor) and partially inhibited by tetraethylammonium (TEA; a non-selective potassium channel blocker) and charybdotoxin (a large- and intermediate-conductance calcium-activated potassium channel blocker). In contrast, atropine (a muscarinic receptor antagonist) or pyrilamine(a histamine H1 receptor antagonist) had no effect. Furthermore, oral administration of HEPP (30-300 mg/kg) in anaesthetized rats caused a dose-dependent and sustained hypotensive action. This effect was unchanged by atropine or TEA, but was strongly reduced in rats continuously infused with L-NAME or methylene blue. Moreover, rutin (1-3 mg/kg) administered by an intravenous route also caused a dose-dependent hypotensive effect in rats. Our results demonstrated that the extract obtained from P. paniculata induces potent hypotensive and vasorelaxant effects that are dependent on the nitric oxide/guanylate cyclase pathway. These effects could be related, at least in part, to the rutin contents in this extract.

The effects of racemic, (+)- and (-)-pinacidil on the membrane potential of the rat aorta.

The endothelium-intact and -denuded rat aorta is hyperpolarized by racemic and (-)-pinacidil, probably by opening ATP-dependent potassium channels. (+)-Pinacidil caused depolarization of the endothelium-intact and -denuded rat aorta. The depolarization induced by 20 mAM KCl in the endothelium-intact rat aorta was reversed by racemic and (-)-, but not by (+)-pinacidil. On the endothelium-intact rat aorta, isoprenaline produced hyperpolarization and ICI 118551 (erythro-(+/-)-1-(7-methylindan-4-yloxy)-3-isopropylamino butan-2-ol) had no effect alone but prevented isoprenaline from causing hyperpolarization. The hyperpolarization induced by isoprenaline was reversed by racemic and (+)-, but not by (-)-pinacidil. Glibenclamide depolarized the endothelium-intact rat aorta and prevented the hyperpolarizing action of racemic pinacidil and (-)-pinacidil. (+)-Pinacidil prevented the hyperpolarizing action of (-)-pinacidil. Glibenclamide is probably preventing the hyperpolarization associated with opening of the ATP-dependent potassium channel by blocking this channel. Several mechanisms may underlie the depolarizing action of (+)-pinacidil, including blocking of ATP-dependent potassium channels.

Role of oxidative stress via miR‐199a in vascular dysfunction of thoracic aorta from diabetic rats

Diabetes is known to be associated with severe cardiovascular dysfunction and hyperglycemia induces alterations in intracellular signal transduction cascades, including generation of reactive oxygen species. Although exact mechanism of diabetes-induced vascular changes has not been elucidated yet, increased oxidative stress is one of major contributors to these events. Previously, we demonstrated that an antioxidant treatment can ameliorate cardiac and vascular dysfunction in diabetic rats. MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression at the post-transcriptional level and have shown that there are close relationship between functional changes and altereation in miRNAs including miR-199a due to duration of diabetes. In that regard, we aimed to investigate the role of miR-199a in oxidative stress-induced vascular dysfunction using an antioxidant, selenium in diabetic rats. Thoracic aorta from diabetic rats showed alteration of multiple miRNAs by array analysis. We further investigated the aorta by using real-time PCR of miRNAs, which are closely related with diabetic cardiomyopathy. PCR analysis of miR-199a demonstrated that there is a downregulation (25% compaered to control) in miR-199a level of endothelium-intact aorta from diabetic rats which is fully prevented with sodium selenate treatment. These results fully coincide with functional data. Taken together, it can be proposed a possible relation between increased oxidative stress, downregulation of miR-199a and endothelial vaascular dysfunction in diabetic rats. (Supported by TUBITAK-SBAG-109S267)

Pharmacological Activity of Novel 2-Hydroxyacetophenone Isatin Derivatives on Cardiac and Vascular Smooth Muscles in Rats

Isatin (1H-indole-2,3 dione) is an endogenous compound with biological activities. Many of its derivatives have pharmacological effects, including inhibition of cyclic guanosine monophosphate levels in cardiac tissue; sedative-hypnotic profiles; anticonvulsant, analgesic, antithermic, and anti-inflammatory activities; and anxiolytic, antimicrobial, and proapoptotic effects. Carbamates derived from isatin have a vasorelaxant profile. This study investigated the activity of 2 novel 2-hydroxyacetophenone derivatives of isatin (named MB101 and MB130) on the contractility of rat aorta and papillary muscles. Both compounds induced a concentration-dependent relaxation (5-100 μM) in the endothelium-intact aorta that was abolished by N-nitro-L-arginine methyl ester. Atropine, a muscarinic receptor antagonist, significantly prevented vasodilatation of 100 μM MB101. In contrast, atropine caused no significant alteration in MB130-induced vasorelaxation. Naloxone, a nonselective opioid receptor antagonist, completely prevented the relaxing effect of MB101 and MB130 at all concentrations. In papillary muscles, only MB130 induced a significant depression, and this contractile response was not altered by propranolol and atropine. Both the compounds reduced systolic and diastolic pressures in a dose-dependent manner in anesthetized rats. The 2-hydroxyacetophenones produced direct effects on vascular tonus through either muscarinic or opioid pathways. MB130 produced cardiac depression by opioid receptors and bradykinin because pretreatment HOE140 or with naloxone, an antagonist of type-2, bradykinin were able to partially block the decrease in twitch amplitude in papillary muscles induced by MB130. These findings provide information for designing new strategies for the treatment of cardiovascular disorders.

Inhibitory Effect of Fentanyl on Phenylephrine-Induced Contraction on Rabbit Aorta

This in vitro study was designed to assess the effects of fentanyl on isolated rabbit thoracic aorta rings contracted with phenylephrine. Methods included contraction of aorta rings with phenylephrine (10–5 M) and recording the changes after increasing concentrations of fentanyl (10–9 M – 10–5 M). Similar experiments were done after incubation with Nω- nitro-L-arginine methyl ester (10–4 M), indomethacin (10-5 M), naloxone (10–5 M), ouabain (10–5 M), TEA (10–4 M) and glibenclamide (10–5 M). It was revealed that, fentanyl causes relaxation in rabbit aorta rings precontracted with phenylephrine. Removal of endothelium significantly reduces the relaxant response to fentanyl. Nitric oxide synthase inhibitor L-NAME, K+ channel blocker glibenclamide and Na+/K+ ATPase inhibitor ouabain inhibits the relaxant effect of fentanyl in endothelium intact aorta rings. These results suggest that fentanyl causes dose dependent vasodilatation in the rabbit aorta via activation of KATP channels and Na+-K+ -ATPase, and nitric oxide released from endothelium.

Vasorelaxant Activities of Aqueous Extracts from Twenty Medicinal Plants Used in Oriental Medicines in Isolated Rat Aorta

Water extracts from 20 medicinal plants, traditionally used for postmenopausal symptoms in Korea, were examined for their vasorelaxant activity in isolated rat thoracic aorta rings precontracted with norepinephrine (NE). Among the 20 medicinal plants, Cornus officinalis (CoEx, 0.3 ㎎/mL), Schisandra chinensis (ScEx, 0.3 ㎎/mL), Erythrina variegate (EvEx, 0.3 ㎎/mL), and Epimedium koreanum (EkEx, 0.3 ㎎/mL) showed rapid relaxation of endothelium-intact aorta (69±4%, 40±3%, 25±2%, and 23±3% of active tone induced by NE, respectively). In contrast, the extracts of Erythrina variegata (EvEx), Angelica gigas (AgEx), Pueraria thunbergiana (PtEx), and EkEx lead to gradual (i.e., long-term) relaxation to baseline in endothelium-intact vessels. The time to complete relaxation was 20～40 min. These 6 plant extracts were selected for the investigation of possible underlying mechanisms. The CoEx-, ScEx-, or EkEx-induced rapid relaxations were virtually abolished by endothelium denudation, and were significantly inhibited by pretreatment with nitric oxide (NO) synthase inhibitor N G -nitro-L-arginine (L-NNA, 10 μM), indicating that increased formation of NO might contribute to the endothelium-mediated relaxation. In long-term responses, the endothelium denudation did not affect PtEx-induced relaxation, whereas it delayed responses by EvEx and AgEx, and significantly inhibited the effect of EkEx. Among EvEx, AgEx, and PtEx, EvEx attenuated the CaCl₂-induced vasoconstriction in high-potassium depolarized medium, implying that EvEx is involved in inhibition of the extracellular calcium influx to smooth muscle through voltage dependent calcium channels. These results provide the scientific rationale for the interrelationships between the use of 20 medicinal plants and their effects on cardiovascular health in estrogen deficient conditions.

Vasoactive effects of different fractions from two Panamanians plants used in Amerindian traditional medicine

Ethnopharmacological relevance Cecropia obtusifolia (Cecropiaceae) and Psychotria poeppigiana (Synonym: Cephaelis elata, Rubiaceae) are two Latin American plants broadly used in traditional Amerindian medicine. The former, together with many other species of the genus Cecropia, share the folk reputation of curing heart failure, cough, asthma and bronchitis. The latter is used in Panama by Kuna and Ngäbe Buglé (Guaymies) native Indians for the treatment of dyspnea. Aim of the study Based on screening of selected medicinal Panamanian plants by radioligand-binding techniques by Caballero-George et al. (2001), the present study was carried out in order to investigate the vasoactive effects of different fractions from both P. poeppigiana and C. obtusifolia on rat thoracic aorta and identify active fractions and their chemical constituents. Materials and methods Both acid and neutral methanol fractions (P-AMeOH and P-NMeOH) and acid and neutral dichlorometane fractions (P-ADCM and P-NDCM) were obtained from P. poeppigiana crude methanolic and dichlorometane extracts, respectively. Identical fractionation was carried out for C. obtusifolia (C-AMeOH, C-NMeOH, C-ADCM and C-NDCM. Vasorelaxant effect of all fractions, and their inhibition of contractile responses to angiotensin II were evaluated in isolated aortic rings. Results P-AMeOH, P-NMeOH and P-ADCM fractions induced a concentration-dependent relaxation (43.9 ± 1.8%, 35.3 ± 4.7% and 52.9 ± 3.5%, respectively) in the endothelium-intact aorta precontracted by phenylephrine (PE, 10 −6 M). The relaxation produced by C-AMeOH and C-NMeOH (57.3 ± 2.5% and 53.3 ± 3.3%, respectively) was greater than the effect produced by C-ADCM and C-NDCM (42.2 ± 3.4% and 21.8 ± 0.8%, respectively). Only the incubation of the aortic rings with P-AMeOH reduced the maximum contraction induced by angiotensin II at 20.08 ± 0.55%. Conclusions The direct vasorelaxation effect observed could explain in part the ethnomedical use of these plants in Amerindian traditional medicine. The most active fractions contain phenolic and aromatic acid compounds. Furthermore, P-AMeOH, the only fraction that showed both vasorelaxant effect and inhibition of contractile responses to angiotensin II, is the most rich in aromatic acids compounds and the only one that contains scopoletin.

Methylglyoxal Enhances Sodium Nitroprusside–Induced Relaxation in Rat Aorta

The concentration of methylglyoxal (MGO), a metabolite of glucose, increases in plasma of type II diabetic patients as well as in tissues of hypertensive rats. We have previously shown that MGO inhibited noradrenaline (NA)–induced smooth muscle contraction in rat aorta. However, the effect of MGO on relaxing responses in isolated blood vessel remains to be clarified. Thus, we examined if MGO affects acetylcholine (ACh)– or sodium nitroprusside (SNP)– induced vasodilation on NA (100 nM)–induced pre-contraction in rat thoracic aorta. Treatment of endothelium-intact aorta with MGO (420 μM, 30 min) did not change ACh (1 nM – 3 μM)–induced endothelium-dependent relaxation. In contrast, treatment of endothelium-denuded aorta with MGO shifted the concentration–response curve for SNP (0.1 – 300 nM) to the left. MGO increased reactive oxygen species (ROS) production in smooth muscle on analysis of protein carbonylation. Anti-oxidant agents such as tempol (10 μM), catalase (5000 U/mL), and nitric oxide synthase inhibitor, NG-nitro-l-arginine methylester (100 μM) had no effect on MGO-induced enhancement of SNP-induced relaxation. However, iberiotoxin (100 nM), a large-conductance Ca2+-activated K+ (BK Ca)–channel inhibitor, significantly prevented the effect. The present study revealed that MGO enhanced SNP-induced relaxation in a ROS-independent manner via in part opening smooth muscle BK Ca channels.

Relaxing Effects of Phytoestrogen α-Zearalanol on Rat Thoracic Aorta Rings in Vitro

The aim of this research is to investigate the vasorelaxing effects and mechanisms involved in the phytoestrogen alpha-zearalanol (alpha-ZAL) in rat thoracic aortas rings. Intact or endothelium denuded rat thoracic aortas rings were put in individual organ chamber to observe the endothelium-dependent or independent vasorelaxing effects of alpha-ZAL (10(-10)-10(-5) M). The thoracic aortas rings were pre-contracted with phenylephrine. The relaxing effects of alpha-ZAL were observed and the influence of N(omega)-nitro-L-arginine methylester (L-NAME, NOS inhibitor), methylene blue (MB, guanylate cyclase inhibitor), charybdotoxin (ChTX, Ca(2+)-activated K+ channel blocker), glibenclamide (ATP-sensitive K+ channel blocker), (-) BayK8644 (L-type Ca2+ channel agonist) and ICI182,780 (estrogen receptor antagonist) were pre-incubated with alpha-ZAL, respectively, to explore the possible mechanisms involved in this vasorelaxation. Furthermore, the Phospho-eNOS expression and cGMP level in the aortas tissue were detected by Western blot and radioimmunity, respectively; the NO level in perfusate was assaied by chromatometry. Our result showed that alpha-ZAL (10(-10)-10(-5) M) induced both endothelium-dependent and -independent relaxation of rat thoracic aortas rings. The vasorelaxing effects of alpha-ZAL were dose-dependent whether the endothelium was intact or not. In endothelium-intact aortas rings, alpha-ZAL-induced vasorelaxation might be inhibited by L-NAME, MB, charybdotoxin, glibenclamide and (-) BayK8644, but not ICI182,780. (-) BayK8644 could also inhibit alpha-ZAL-induced vasorelaxation in endothelium-denuded aortas rings.10(-7)-10(-5) M alpha-ZAL might induce the Phospho-eNOS expression in thoracic aorta tissue, increase the NO level in perfusate and cGMP content in thoracic aorta tissue. Meanwhile, L-NAME might decrease both NO and its downstream cGMP level. Methylene blue might decrease the level of cGMP. These results suggest that alpha-ZAL induces a partly endothelium-dependent relaxation of rat thoracic aortas rings; the possible mechanisms involved in this rapid vasorelaxation include activation of eNOS/NO/cGMP pathway, opening of VSMCs ATP-sensitive and Ca(2+)-activated K+ channels through secretion of EDHF from endothelium. Furthermore, this relaxation also appears to be mediated by both direct and indirect inhibition of voltage-dependent Ca2+ channel of VSMCs, while it is not concerned with activation of estrogen receptor.

Antihypertensive and vasorelaxant effects of tilianin isolated from Agastache mexicana are mediated by NO/cGMP pathway and potassium channel opening

Current investigation was undertaken to elucidate the mode of action of tilianin, isolated from Agastache mexicana, as a vasorelaxant agent on in vitro functional rat thoracic aorta test and to investigate the in vivo antihypertensive effect on spontaneously hypertensive rats (SHR). Tilianin (0.002–933 μM) induced significant relaxation in a concentration- and endothelium-dependent and -independent manners in aortic rings pre-contracted with noradrenaline (NA, 0.1 μM), and serotonin (5-HT, 100 μM). Effect was more significant ( p < 0.05) in endothelium-intact (+E) aorta rings than when endothelium was removed (−E). Pre-treatment with N-nitro- l-arginine methyl ester ( l-NAME; 10 μM) or 1- H-[1,2,4]-oxadiazolo-[4,3a]-quinoxalin-1-one (ODQ, 1 μM) produced a significant change of the relaxant response and activity was markedly inhibited, but not by indomethacin (10 μM) or atropine (1 μM). Furthermore, tilianin (130 μM) provoked a significant displacement to the left in the relaxation curve induced by sodium nitroprusside (SNP; 0.32 nM to 0.1 μM). Moreover, tilianin induced significant in vitro NO overproduction (1.49 ± 0.86 μM of nitrites/g of tissue) in rat aorta compared with vehicle ( p < 0.05). In addition, pre-treatment with tetraethylammonium (TEA, 5 mM) and 2-aminopyridine (2-AP, 0.1 μM) shifted to the right the relaxant curve induced by tilianin ( p < 0.05). Finally, a single oral administration of tilianin (50 mg/kg) exhibited a significant decrease in systolic and diastolic blood pressures ( p < 0.05) in SHR model. Results indicate that tilianin mediates relaxation mainly by an endothelium-dependent manner, probably due to NO release, and also through an endothelium-independent pathway by opening K + channels, both causing the antihypertensive effect.