Synthesis and antimalarial evaluation of novel pyridine quinoline hybrids

Abstract  Synthesis and evaluation of the antimalarial activity of new pyridine quinoline hybrid molecules against a chloroquine-susceptible strain of Plasmodium falciparum and as inhibitors of β-hematin formation are described. Two novel pyridine quinoline hybrid molecules and one bisquinoline molecule were synthesized and purified by column chromatography and evaluated for antimalarial and haem polymerization inhibition (HPIA) activities. The molecules were found to be very good haem polymerization inhibitors but showed poor antimalarial activity. This was attributed to their low vacuole accumulation ratio (VAR) in comparison to chloroquine. These molecules can be used as templates for designing new antimalarials targeting haem detoxification pathway of malaria parasite. Graphical Abstract   Synthesis and antimalarial evaluation of novel pyridine quinoline hybrids B.N Acharya, D. Thavaselvam^# and M.P Kaushik^* Discovery Centre, Process Technology Development Division Defence R & D Establishment, Jhansi Road, Gwalior-474002 (MP) INDIA ^#Division of Microbiology, Defence Research and Development Establishment,Gwalior-474002, India Synthesis and evaluation of antimalarial activity of new pyridine–quinoline hybrid molecules against a chloroquine-susceptible strain of Plasmodium falciparum and as inhibitors of β-hematin formation are described.     

Potent antimalarial activity of newly synthesized substituted chalcone analogs in vitro

Abstract   Several new chalcone analogues were synthesized and evaluated as inhibitors of malaria parasite. Inhibitory activity was determined in vitro against a chloroquine-sensitive Plasmodium falciparum strain of parasites. The compound 3-(4-methoxyphenyl)-1-(4-pyrrol-1-yl-phenyl)prop-2-en-1-one was found to be the most active with 50% inhibition concentration (IC₅₀) of 1.61 μg/ml. This inhibitory concentration is comparable to a prototype phytochemical chalcone, licochalcone A, with an IC₅₀ of 1.43 μg/ml. The present study suggests that small, lipophilic nitrogen heterocyclic ring A together with small hydrophobic functionality at ring B can enhance antimalarial activity. These results suggest that chalcones are a class of compounds that provides an option of developing inexpensive, synthetic therapeutic antimalarial agents in the future. Graphical Abstract  Claisen-Schmidt condensation method was employed to synthesize various substituted chalcones. Among all, 3-(4-Methoxyphenyl)-1-(4-pyrrol-1-yl-phenyl)prop-2-en-1-one was found to be most effective with IC₅₀ value of 1.6 μg/ml in vitro against chloroquine sensitive strain (3D7) of Plasmodium falciparum.      

Antiplasmodial and antitrypanosomal activity of plants from the Kingdom of Saudi Arabia

The antiplasmodial and antitrypanosomal activity of the methanol extracts of 42 plants collected from the Kingdom of Saudi Arabia and some fractions obtained thereof were evaluated. The antiplasmodial activity was tested in vitro against chloroquine-resistant strain (K1) and sensitive strain (FCR3), and the antitrypanosomal activity was tested in vitro against Trypanosoma brucei brucei GUTat 3.1 strain. For host cells, the cytotoxicity of the active extracts was also evaluated against the MRC5 human cell line. Only extracts of three samples demonstrated good antiplasmodial activity (IC₅₀ < 12.5 and > 1.56 μg/ml, score 2), the methanol extracts of Lycium shawii, Heliotropium zeylanicum and the petroleum ether-soluble fraction of the methanol extract of Caralluma tuberculata, while extracts of the remaining 42 plants were inactive (IC₅₀ > 12.5 μg/ml, score 1). As for the antitrypanosomal activity, the methanol extract of Solanum schimperianum demonstrated the highest activity (IC₅₀ 0.061 μg/ml), followed by the petroleum ether-soluble fraction of the methanol extract of C. tuberculata (IC₅₀ 0.5 μg/ml). The chloroform-soluble fraction of the methanol extract of C. tuberculata was moderately active (IC₅₀ 3.5 μg/ml), with low cytotoxicity (IC₅₀ 62.6 μg/ml) and moderate selectivity index (SI 17.9). The methanolic extracts of 34 plants showed good activity with score 2 (IC₅₀ < 12.5 and > 1.56 μg/ml), while the extracts of seven plants were inactive (IC₅₀ > 12.5 μg/ml, score 1).     

Antioxidant and antilisterial effect of seed essential oil and organic extracts from Zizyphus jujuba

Hydrodistilled volatile oil from the seeds of Zizyphus jujuba was analyzed by GC–MS. Twenty three compounds representing 91.59% of the total oil was identified. The oil and organic extracts revealed a great potential of antilisterial effect against all five strains of Listeria monocytogenes ATCC 19111, 19116, 19118, 19166 and 15313. Also the oil had strong detrimental effect on the viable count of the tested bacteria. The samples were also subjected to screening for the antioxidant activity by using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and superoxide radicals scavenging activities assay. In the first case, the IC₅₀ value of the Z. jujuba essential oil was determined to be 5.21 ± 0.01 μg/ml. Among the extracts, the strongest activity was exhibited by the methanol extract with an IC₅₀ value of 20.44 ± 0.18 μg/ml. In the superoxide radicals scavenging activities assay, methanol extract was superior to all other extracts (IC₅₀ = 18.60 ± 0.3 μg/ml). Furthermore, the amount of total phenolic compounds was determined. The results indicate that the essential oil and extracts of Z. jujuba could serve as natural antimicrobial and antioxidant agents for the food industry.     

Brazilian marine sponge <Emphasis Type="Italic">Polymastia janeirensis</Emphasis> induces apoptotic cell death in human U138MG glioma cell line,but not in a normal cell culture

Summary  Marine sponges have been prominently featured in the area of cancer research. Here, we examined the anti-proliferative effects of crude extracts (aqueous and organic) of the Brazilian marine sponge Polymastia janeirensis in the U138MG human glioma cell line. Moreover, we examined the effects of extracts on selective cytotoxicity in the glioma cells in comparison with a normal cell culture. Exposure of glioma cells to treatments (24 h) resulted in cell number decrease at all doses tested, with both aqueous and organic extracts (IC₅₀ <20 and <30 μg/ml, respectively). Parallel to this result, sponge extracts reduced glioma cell viability (IC₅₀ <15 μg/ml for both extracts). However, higher doses (50 and 100 μg/ml) induced a stronger cytotoxic effect when compared to the lower dose tested (10 μg/ml), inhibiting more than 80% of cellular growth and viability. Propidium iodide uptake and flow cytometry analysis further showed that sponge extracts caused necrosis in the glioma cell line at higher doses, while a high percentage of apoptotic glioma cells were observed at 10 μg/ml. Moreover, apoptosis was prevented by the pan-caspase inhibitor Z-VAD, suggesting that marine sponge extracts, at lower doses, induce caspase-dependent apoptosis in U138MG glioma cells. Surprisingly the extracts herein tested were more effective than temozolomide, a potent inductor of apoptosis used for the treatment of malignant gliomas. Furthermore, our results suggested a selectivity cytotoxic effect on glioma cell line in comparison with a normal cell culture, since the effect on viability found in glioma cells was not observed in astrocyte cultures with the lower dose (10 μg/ml). Thus, this marine sponge may be considered a good candidate for development of new cancer medicines with antitumor activity against gliomas.     

Inhibitory effects of compounds from Anemarrhenae Rhizoma on α-glucosidase and aldose reductase and its contents by drying conditions

An aqueous extract of Anemarrhena asphodeloides Bunge (Anemarrhenae Rhizoma) showed inhibitory effects on α-glucosidase and aldose reductase (AR). We obtained two active compounds, mangiferin (α-glucosidase: IC₅₀ = 96.1 μg/ml, AR:IC₅₀ = 0.13 μg/ml) and mangiferin 7-O-β-D-glucopyranoside (α-glucosidase: IC₅₀ = 158 μg/ml, AR:IC₅₀ = 65.7 μg/ml ), from Anemarrhenae Rhizoma. In addition, the amount of mangiferin in Anemarrhenae Rhizoma changed with the method of preparation (drying conditions), namely, low-temperature, long-term drying conditions and harvesting in August were most effective.     

Inhibitory effect of Yunnan traditional medicines on hepatitis C viral polymerase

For the purpose of developing novel anti-hepatitis C virus (HCV) agents from natural resources, 93 Yunnan crude drugs were screened for their inhibitory effects on RNA-dependent RNA polymerase (RdRp) of HCV. Although 71 methanol extracts and 50 water extracts inhibited HCV-RdRp by more than 50% at a concentration of 50 g/ml, the majority of them contained a high percentage of tannins. However, methanol extracts of Plumbago zeylanica (branch), Maytenus fookerii (leaf) and Huashidancha (Y61, branch and leaf), and water extracts of Potentilla griffithii (whole plant) and Salvia yunnanensis (underground part), having IC₅₀ values of less than 10 g/ml, showed less than 10% tannin content. In addition, from a methanol extract of Tripterygium hypoglaucum (root bark), demethylzeylasteral was isolated as a strongly inhibitory substance against HCV-RdRp.     

Antioxidant and antidermatophytic activities of essential oil and extracts of Magnolia liliflora Desr.

This study was carried out to assess the antioxidant and antidermatophytic activities of the essential oil and extracts of Magnolia liliflora Desr. Antioxidant activity was evaluated by using 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay. The free radical scavenging activities of the oil and ethyl acetate extract were found to be superior (IC₅₀ values = 10.11 and 16.17 μg/ml, respectively) as compared to butylatedhydreoxyanisole (BHA), (IC₅₀ value = 18.27 μg/ml). Also the ethyl acetate extract revealed the highest phenolic contents (96.13 mg/g of dry wt) as compared to the other extracts. Further, the oil (1000 μg/disc) and extracts (1500 μg/disc) revealed 42.36–63.12% and 19.07–54.14% antidermatophytic effect, respectively along with their respective MIC values ranging from 62.5 to 500 and 250 to 2000 μg/ml against the members of Trichophyton and Microsporum spp. Also the oil had strong detrimental effect on spore germination of tested fungal pathogens as well as concentration and time dependent kinetic inhibition of Microsporum canis KCTC 6348. The results of this study justify a potential role of M. liliflora to serve as a natural antioxidant and antidermatophytic agent.     

Antibacterial, antioxidant and cytotoxic activities of extracts of Conyza canadensis (L.) Cronquist growing in Tunisia

Antibacterial antioxidant and cytotoxic activities of petroleum ether, ethyl acetate and methanol extracts of Conyza Canadensis (L.) Cronquist were investigated. Antibacterial activity was evaluated using the agar diffusion and microwell dilution assays against four strains of bacteria. Antioxidant activity was measured by the 1,1-diphenyl-2-picrylhydrazyl (DPPH) method and the cytotoxic activity was tested against Hep-2 cells (laryngeal carcinoma cell line) using methylene blue assays. Among tested extracts, the methanolic extract exhibited important antibacterial activity. It also showed good antioxidant activity with 50% inhibition concentration (IC₅₀) of 120 μg/ml. Cytotoxicity of extracts was time depend, increasing with exposure time and concentration. At 72 h of incubation, the ethyl acetate and petroleum ether extracts demonstrated effective cytotoxic activity against Hep-2 cells with IC₅₀ values of 45 and 50 μg/ml, respectively.     

Neolignans from North American Magnolia Species with Cyclooxygenase 2 Inhibitory Activity

Objectives:  Based upon reported ethnomedicinal use by Native Americans, extracts and pure isolates from leaves and seeds of Magnolia grandiflora, M. virginiana, M. acuminata and M. macrophylla, all native to the Southeastern United States, were investigated for their anti-inflammatory potential against cyclooxygenase 2 (COX-2). Material and methods:  The extracts and pure compounds from Magnolia species were tested for their production of prostaglandin E₂ (PGE₂) using a mouse macrophage (RAW 264.7) assay where cells were stimulated by lipopolysaccharide. Results:  Leaf extracts were moderately active (44–58% inhibition at 50 μg/ml) whereas seed extracts showed significant activity of 54–88% inhibition, respectively. In the seed extract of M. grandiflora, honokiol, magnolol and 4’-O-methylhonokiol strongly inhibited COX-2 (IC₅₀: 1.2–2.0 μg/ml), 3-O-methylmagnolol was moderately active while a new compound was inactive towards COX-2. The neolignans were not cytotoxic to macrophages (RAW 264.7) and kidney fibroblast (VERO) cells in vitro. Conclusions:  The results indicate that the reported ethnomedicinal use of the investigated Magnolia species is in agreement with anti-inflammatory activity of their respective compounds. Received 8 December 2007; accepted 16 January 2009     

In vitro antioxidant activity and total phenolic content of ethanolic leaf extract of Stevia rebaudiana Bert.

The aim of this study was to assess the in vitro potential of ethanolic leaf extract of Stevia rebaudiana as a natural antioxidant. The DPPH activity of the extract (20, 40, 50, 100 and 200 μg/ml) was increased in a dose dependent manner, which was found in the range of 36.93–68.76% as compared to ascorbic acid 64.26–82.58%. The IC₅₀ values of ethanolic extract and ascorbic acid in DPPH radical scavenging assay were obtained to be 93.46 and 26.75 μg/ml, respectively. The ethanolic extract was also found to scavenge the superoxide generated by EDTA/NBT system. Measurement of total phenolic content of the ethanolic extract of S. rebaudiana was achieved using Folin–Ciocalteau reagent containing 61.50 mg/g of phenolic content, which was found significantly higher when compared to reference standard gallic acid. The ethanolic extract also inhibited the hydroxyl radical, nitric oxide, superoxide anions with IC₅₀ values of 93.46, 132.05 and 81.08 μg/ml, respectively. However, the IC₅₀ values for the standard ascorbic acid were noted to be 26.75, 66.01 and 71.41 μg/ml respectively. The results obtained in this study clearly indicate that S. rebaudiana has a significant potential to use as a natural antioxidant agent.     

Protective effect of the ethanol extract of <Emphasis Type="Italic">Magnolia officinalis</Emphasis> and 4-<Emphasis Type="Italic">O</Emphasis>-methylhonokiol on scopolamine-induced memory impairment and the inhibition of acetylcholinesterase activity

Magnolol, honokiol, and obovatol are well-known bioactive constituents of the bark of Magnolia officinalis and have been used as traditional Chinese medicines for the treatment of neurosis, anxiety, and stroke. We recently isolated novel active compound (named 4-O-methylhonokiol) from the ethanol extract of Magnolia officinalis. The present study aimed to test two different doses of ethanol extracts of Magnolia officinalis (5 and 10 mg/kg/mouse, p.o., 1 week) and 4-O-methylhonokiol (0.75 and 1.5 mg/kg/mouse, p.o., 1 week) administered for 7 days on memory impairment induced by scopolamine (1 mg/kg body weight i.p.) in mice. Memory and learning were evaluated using the Morris water maze and the step-down avoidance test. Both the ethanol extract of Magnolia officinalis and 4-O-methylhonokiol prevented memory impairment induced by scopolamine in a dose-dependent manner. The ethanol extract of Magnolia officinalis and 4-O-methylhonokiol also dose-dependently attenuated the scopolamine-induced increase of acetylcholinesterase (AChE) activity in the cortex and hippocampus of mice, and inhibited AChE activity in vitro with IC₅₀ (12 nM). This study, therefore, suggests that the ethanol extract of Magnolia officinalis and its major ingredient, 4-O-methylhonokiol, may be useful for the prevention of the development or progression of AD.     

Cytotoxic activity of Perilla frutescens var. japonica leaf extract is due to high concentrations of oleanolic and ursolic acids

Three triterpene acids, ursolic acid (1), corosolic acid (2), and oleanolic acid (7), were isolated from the ethanol extract of leaves of Perilla frutescens (L.) Britton var. japonica Hara (Labiatae; Japanese name: Egoma). These acids are the active principles responsible for the cytotoxicity against three cultured human tumor cell lines, HL-60 (leukemia carcinoma), MCF-7 (breast carcinoma), and Hep-G2 (hepatic carcinoma), with half maximal inhibitory concentration (IC₅₀) values of 12–48 μM.     

Free radical scavenging and antiatherogenic activities of Sesamum indicum seed extracts in chemical and biological model systems

An emerging consensus underscores the importance of oxidative events in vascular disease including excess production of reactive oxygen/nitrogen species (ROS/RNS), in addition to lipoprotein oxidation. Sesamum indicum has long been used extensively as a traditional food. The aim of present study was to evaluate antioxidant action of aqueous and ethanolic seed extracts from S. indicum using various in vitro ROS/RNS generated chemical and biological models. Results demonstrated that the graded-dose (25–1000 μg/ml) of aqueous and ethanolic extracts markedly scavenged the nitric oxide, superoxide, hydroxyl, 1,1-diphenyl-2-picrylhydrazyl and 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) radicals and, showed metal chelating ability as well as reducing capacity in Fe³⁺/ferricyanide complex and ferric reducing antioxidant power assays. In biological models, both extracts were found to inhibit metal-induced lipid peroxidation in mitochondrial fractions, human serum and LDL oxidation models. In lipoprotein kinetics study, both extracts significantly (P < 0.05) increased lag phase time along with reduced oxidation rate and conjugated dienes production. Ethanolic extract of S. indicum showed higher amounts of total polyphenol and flavonoid content as compared to their counterpart. The IC₅₀ values of both extracts were compared with respective antioxidant standards. Overall, ethanolic extract of S. indicum possess strong antioxidant capacity and offering effective protection against LDL oxidation susceptibility.     

Anti-oxidative and inhibitory activities on nitric oxide (NO) and prostaglandin E<Subscript>2</Subscript> (COX-2) production of flavonoids from seeds of <Emphasis Type="Italic">Prunus tomentosa</Emphasis> Thunberg

Chemical investigation of the 80% Me₂CO extract from the seeds of Prunus tomentosa led to the isolation and identification of six flavonoids: kaempferol (1), kaempferol 3-O-α-L-rhamnopyranoside (2; afzelin), kaempferol 3-O-β-D-(6-acetyl)-glucopyranosyl(1→4)-α-L-rhamnopyranoside (3; multiflorin A), kaempferol 3-O-β-D-glucopyranosyl(1→4)-α-L-rhamnopyranoside (4; multiflorin B), quercetin 3-O-α-L-rhamnopyranoside (5; quercitrin), and quercetin 3-O-β-D-glucopyranosyl (1→4)-α-L-rhamnopyranoside (6; multinoside A). Anti-oxidative and inhibitory activities on nitric oxide (NO) and prostaglandin E₂ production in interferon-γ (INF-γ) and lipopolysaccharide (LPS)-activated RAW 264.7 cells in vitro (COX-2) of the isolated compounds were evaluated. Compounds 1, 5, and 6 exhibited potent anti-oxidative activity in the DPPH radical scavenging assay with IC₅₀ values of 57.2, 59.4, and 54.3 μg/mL respectively. The positive control, ascorbic acid, had an IC₅₀ of 55.5 μg/mL. Compounds 1, 5, and 6 also reduced COX-2 levels in a dose dependent manner with IC₅₀ values of 10.2, 8.7, and 9.6 μg/mL respectively, with the positive control, indomethacin, having an IC₅₀ of 5.1 μg/mL. All six compounds inhibited NO production in a dose dependent manner with IC₅₀ values of 35.1, 42.8, 40.0, 44.8, 43.7, and 43.9 μg/mL respectively, while the positive control, L-NMMA, had an IC₅₀ of 42.1 μg/mL.     

Anti-oxidative and anti-inflammatory activities of some isolated constituents from the stem bark of Allanblackia monticola Staner L.C (Guttiferae)

Stem bark of Allanblackia monticola has been used in association with others plant in the Cameroonian folk medicine for the treatment of various diseases such amoebic dysentery, diarrhoea, lung infections, and skin diseases. The methylene chloride fraction, its isolated compounds like α-mangostin, lupeol and acid betulinic were screened for antioxidant activity using free radical scavenging method. These isolated compounds were further tested for anti-inflammatory properties using carrageenan-induced model. Methylene chloride fraction, showed concentration-dependent radical scavenging activity, by inhibiting 1,1-diphenyl-1-picryl-hydrazyl radical (DPPH) with an IC₅₀ value of 14.60 μg/ml. α-Mangostin and betulinic acid (500 μg/ml), showed weak radical scavenging activity with a maximum inhibition reaching 38.07 μg/ml and 26.38 μg/ml, respectively. Betulinic acid, lupeol and α-mangostin (5 mg/kg and 9.37 mg/kg) showed anti-inflammatory activity with a maximum inhibition of 57.89%, 57.14% and 38.70%, respectively. Methylene chloride fraction of Allanblackia monticola and some derivatives, have antioxidant and anti-inflammatory activities. Received 7 July 2008; accepted 7 October 2008     

Isolation of a multidrug resistance inhibitor fromAconitum pseudo-laeve var.erectum

To overcome multidrug resistance (MDR) in cancer chemotherapy, we prepared various plant extracts and searched for a component which is effective for inhibition of MDR. MDR inhibition activity was determined by measuring cytotoxicity to MDR cells using multidrug resistant human fibrocarcinoma KB V20C, which is resistant to 20 nM vincristine and expresses high level ofmdr1 gene. Of various plant extracts, the MeOH extract of the root ofAconitum pseudo-laeve var.erectum was found to have potent inhibitory activity on MDR. The bioassay-guided fractionation of the MeOH extract of the plant led to the isolation of an alkaloid, lycaconitine, as an active principle. And the IC₅₀ of lycaconitne for KB V20C cells was 74 μg/ml.     

Relaxant and antispasmodic effects of extracts of the orchid <Emphasis Type="Italic">Encyclia michuacana</Emphasis> on isolated guinea pig ileum

The antispasmodic effects of hexane-, chloroform-, methanol- and water-extracts of the orchid Encyclia michuacana were studied in vitro on guinea pig ileum against three spasmogens: acetylcholine (Ach), histamine and barium chloride. The chloroform extract exerted a significant antispasmodic effect on ileum contractions induced by Ach, histamine and barium chloride (IC₅₀ = 90.64, 73.12 and 115.2 μg/mL, respectively). Furthermore, the chloroform extract of E. michuacana provoked a concentration-dependent inhibition of spontaneous contractions of guinea pig ileum with potencies comparable to those of papaverine. The antagonism against the spasmogens used suggests that the action of the chloroform extract of E. michuacana could be due mainly to the presence of gigantol. Hexane-, methanol- and water-extracts did not elicit any significant spasmolytic activity.     

Antihyperglycaemic and aldose reductase inhibitory potential of Acacia catechu hard wood and Tectona grandis leaves

The ethanolic extract of Acacia catechu hard wood (Ac) and the ethanolic as well as aqueous extracts of Tectona grandis leaves (Tg) showed marked antihyperglycaemic activity in both normoglycaemic and streptozotocin-induced diabetic rats at 250 mg/kg dose levels. The ethanolic and aqueous extracts of Ac and Tg also showed marked inhibition on AR from eye lens of normal rats with IC 50 values of 9.30 and 9.08 and 3.05, 4.51 μg/ml, respectively. The ethanolic as well as aqueous extracts of both Ac and Tg also showed marked inhibition on AR from eye lens of STZ-induced diabetic rats with IC₅₀ values of 4.70 and 4.91 and 4.71 and 4.83 μg/ml. These results suggest that Acacia catechu hard wood and Tectona grandis leaves could be a new approach in the development of therapeutic or preventive agents for diabetic late-stage complications.     

Antihypertensive and vasorelaxant activities of Laelia autumnalis are mainly through calcium channel blockade

The aim of the present study was to evaluate the possible mechanism of the vasorelaxant action of methanol extract from Laelia autumnalis (MELa) in isolated rat aortic rings, and to establish its antihypertensive activity in vivo. MELa (0.15→50 µg/mL) induced relaxation in aortic rings pre-contracted with KCl (80 mM), showing an IC₅₀ value of 34.61 ± 1.41 µg/mL and E_max value of 85.0 ± 4.38% (in endothelium-intact rings) and an IC₅₀ value of 45.11 ± 4.17 µg/mL and E_max value of 80.0 ± 12.1% (in endothelium-denuded rings). Serotonin (5-HT, 1 × 10^− 4 M) provoked sustained contraction, which was markedly inhibited by MELa (0.15→50 µg/mL) in a concentration-dependent and endothelium-independent manner. Pretreatment with MELa (15, 46, 150, 300 and 1500 µg/mL) also inhibited contractile responses to norepinephrine (NE 1 × 10^− 11 M to 1 × 10^− 5.5 M). In endothelium-denuded rings, the vasorelaxant effect of MELa was reduced partially by ODQ (1 µM), but not by tetraethylammonium (5 µM), glibenclamide (10 µM), and 2-aminopyridine (100 µM). The extract also reduced NE-induced transient contraction in Ca²⁺-free solution, and inhibited contraction induced by increasing external calcium in Ca²⁺-free medium plus high KCl (80 mM). The antihypertensive effect of MELa was determined in spontaneously hypertensive rats (SHR). A single oral administration of the extract (100 mg/kg) exhibited a significant decrease in systolic and diastolic blood pressure and heart rate (p < 0.05) in SHR rats. Our results suggest that MELa induces relaxation in rat aortic rings through an endothelium-independent pathway, involving blockade of Ca²⁺ channels and a possible cGMP enhanced concentrations and also causes an antihypertensive effect.