Cyclic nucleotide crosstalk in salivary glands from partially fed Dermacentor variabilis (Say)

Enzyme immunosorbent assays were used to measure cyclic nucleotide concentrations in homogenates of salivary glands from partially fed female Dermacentor variabilis. The adenylyl cyclase activator forskolin (100 μM) increased homogenate cGMP concentrations greater than three-fold over controls. Competitive inhibition of nitric oxide synthase with 1 mM l-NMMA, an l-arginine analog, demonstrated that crosstalk occurs downstream of nitric oxide synthesis. Forskolin-stimulated synthesis of cGMP was diminished 58% by the soluble guanylyl cyclase inhibitor ODQ (2 μM). The protein kinase A selective inhibitor Rp-cAMPS (50 μM) inhibited forskolin-stimulated cGMP by 49%. Whole glands treated with 10 μM dopamine increased cGMP levels two-fold in the presence of 1 mM IBMX. Treatment of whole salivary glands with equimolar concentrations of 8-Br-cAMP and 8-Br-cGMP produced no greater fluid uptake than in glands treated with 8-Br-cGMP alone, suggesting that cAMP and cGMP share a downstream target. The protein kinase G-selective inhibitor Rp-8-pCPT-cGMPS (100 μM) impeded 10 mM 8-Bromo-cGMP-stimulated gland weight increases. Pretreatment with verapamil, a Ca²⁺ channel blocker, attenuated cyclic nucleotide-stimulated fluid uptake indicating that whole gland fluid changes are dependent on extracellular Ca²⁺. Together, our data suggest that cGMP production is mediated in part by cAMP-dependent activation of soluble guanylyl cyclase. Experiments measuring changes in whole salivary gland weight support the hypothesis that cAMP and cGMP signaling cascades have a common target and that cyclic nucleotide-stimulated fluid movement is dependent on Ca²⁺ influx.     

Plasmodium falciparum: In vitro interaction of quassin and neo-quassin with artesunate, a hemisuccinate derivative of artemisinin

Quassia amara L. (Family Simaroubaceae) is known to have several medicinal properties including the activity against malaria. An HPLC method was employed for purification of the biologically active quassinoids; quassin (Q) and neo-quassin (NQ), further characterized by MALDI-TOF analyses. Purified Q, NQ and the crude bark extract (S1) along with artesunate (AS) were studied for their in vitro anti-plasmodial activity. The in vivo toxicity studies at intraperitoneal doses with higher concentrations of the crude bark extract (S1) in Balb/C mice ruled out the apprehension of toxicity. Interaction studies between the test compounds among themselves (Q + NQ) and individually with artesunate (AS + Q, AS + NQ), were carried out in vitro at four ratios (1:5, 1:2, 2:1 and 5:1) on chloroquine sensitive (MRC-pf-20) and resistant (MRC-pf-303) strains of Plasmodium falciparum. The crude bark extracts of Q. amara exhibited higher P. falciparum inhibitory activity (IC₅₀ = 0.0025 μg/ml) as compared to that of the isolated compounds, quassin (IC₅₀ = 0.06 μg/ml, 0.15 μM), neo-quassin (IC₅₀ = 0.04 μg/ml, 0.1 μM) and also to the positive control, artesunate (IC₅₀ = 0.02 μg/ml, 0.05 μM). The in vitro drug interaction study revealed the compounds, quassin and neo-quassin to be additive to each other. At lower ratios, artesunate was found to be a potential combination partner with both the compounds. It was interesting to note that none of the combinations exhibited antagonistic interactions. This phenomenon offers the opportunity for further exploration of novel therapeutic concentrations and combinations.     

Biological activity of l-2-azetidinecarboxylic acid,isolated from Polygonatum odoratum var. pluriflorum, against several algae

The biological activities of an aqueous fraction extracted from Polygonatum odoratum var. pluriflorum Owhi and of l-2-azetidinecarboxylic acid (AZC), purified from the extract, on the growth of several types of algae were tested. The aqueous fraction was prepared by methanol extraction of P. odoratum var. pluriflorum rhizomes followed by reverse partitioning with butanol. The aqueous extraction inhibited growth of the green alga Chlorella vulgaris by less than 10% at a concentration of 1000 mg L⁻¹. However, growth of the blue-green alga Microcystis aeruginosa was inhibited by 22.0%, 67.9%, and 87.1%, respectively, at 3.1, 6.2, and 12.5 mg extract L⁻¹. AZC was isolated from the aqueous extract and was shown to be the major active substance inhibiting algal growth. AZC concentrations higher than 25 μM inhibited growth, while at 400 μM, growth of the green algae C. vulgaris and Scenedesmus spp. was inhibited by 71.2% and 70.4%, respectively. In contrast, growth of the blue-green algae Anabaena affinis and M. aeruginosa was inhibited at concentrations greater than 1.6 and 0.2 μM, respectively, whereas 92% control required concentrations of 6.3 and 1.6 μM, respectively. AZC also suppressed the growth of the red-tide microalga Cochlodinium polykrikoides by 86.9% and 100% at concentrations of 6.3 and 12.5 μM, respectively. Azetidine and 2-azetidinone showed little activity on the tested algae. The results demonstrate that AZC selectively inhibits algal growth at low concentrations. The green algae C. vulgaris and Scenedesmus spp. were tolerant, whereas M. aeruginosa, A. affinis, and C. polykrikoides were relatively sensitive. Thus, extract and AZC, prepared from P. odoratum rhizomes, showed a potential as natural selective algicide for the control of harmful algae in laboratory assay.     

Respiratory system of Gluconacetobacter diazotrophicus PAL5 Evidence for a cyanide-sensitive cytochrome bb and cyanide-resistant cytochrome ba quinol oxidases

In highly aerobic environments, Gluconacetobacter diazotrophicus uses a respiratory protection mechanism to preserve nitrogenase activity from deleterious oxygen. Here, the respiratory system was examined in order to ascertain the nature of the respiratory components, mainly of the cyanide sensitive and resistant pathways. The membranes of G. diazotrophicus contain Q₁₀, Q₉ and PQQ in a 13:1:6.6 molar ratios. UV_360 nm photoinactivation indicated that ubiquinone is the electron acceptor for the dehydrogenases of the outer and inner faces of the membrane. Strong inhibition by rotenone and capsaicin and resistance to flavone indicated that NADH-quinone oxidoreductase is a NDH-1 type enzyme. KCN-titration revealed the presence of at least two terminal oxidases that were highly sensitive and resistant to the inhibitor. Tetrachorohydroquinol was preferentially oxidized by the KCN-sensitive oxidase. Neither the quinoprotein alcohol dehydrogenase nor its associated cytochromes c were instrumental components of the cyanide resistant pathway. CO-difference spectrum and photodissociation of heme-CO compounds suggested the presence of cytochromes b-CO and a₁-CO adducts. Air-oxidation of cytochrome b (432 nm) was arrested by concentrations of KCN lower than 25 μM while cytochrome a₁ (442 nm) was not affected. A KCN-sensitive (I₅₀ = 5 μM) cytochrome bb and a KCN-resistant (I₅₀ = 450 μM) cytochrome ba quinol oxidases were separated by ion exchange chromatography.     

In silico and in vitro comparative activity of novel experimental derivatives against Leishmania major and Leishmania infantum promastigotes

This in silico and in vitro comparative study was designed to evaluate the effectiveness of some biurets (K1 to K8) and glucantime against Leishmania major and Leishmania infantum promastigotes. Overall, eight experimental ligands and glucantime were docked using AutoDock 4.3 program into the active sites of Leishmania major and Leishmania infantum pteridine reductase 1, which were modeled using homology modeling programs. The colorimetric MTT assay was used to find L. major and L. infantum promastigotes viability at different concentrations of biuret derivatives in a concentration and time-dependent manner and the obtained results were expressed as 50% and 90% of inhibitory concentration (IC₅₀ and IC₉₀). In silico method showed that out of eight experimental ligands, four compounds were more active on pteridine reductase 1. K3 was the most active against L. major promastigotes with an IC₅₀ of 6.8 μM and an IC₉₀ of 40.2 μM, whereas for L. infantum promastigotes was K8 with IC₅₀ of 7.8 μM. The phenylethyl derivative (K7) showed less toxicity (IC₅₀s > 60 μM) in both Leishmania strains. Glucantime displayed less growth inhibition in concentration of about 20 μM. In silico and especially docking results in a recent study were in accordance with the in vitro activity of these compounds in presented study and compound K3, K2 and K8 showed reasonable levels of selectivity for the Leishmania pteridine reductase 1.     

Down-regulation of ether-a-go-go-related gene potassium channel protein through sustained stimulation of AT1 receptor by angiotensin II

We investigated the effects of AT₁ receptor stimulation by angiotensin II (Ang II) on human ether-a-go-go-related gene (hERG) potassium channel protein in a heterogeneous expression system with the human embryonic kidney (HEK) 293 cells which stably expressed hERG channel protein and were transiently transfected with the human AT₁ receptors (HEK293/hERG). Western-blot analysis showed that Ang II significantly decreased the expression of mature hERG channel protein (155-kDa band) in a time- and dose-dependent manner without affecting the level of immature hERG channel protein (135-kDa band). The relative intensity of 155-kDa band was 64.7 ± 6.8% of control (P < 0.01) after treatment of Ang II at 100 nM for 24 h. To investigate the effect of Ang II on the degradation of mature hERG channel protein, we blocked forward trafficking from ER to Golgi with a Golgi transit inhibitor brefeldin A (10 μM). Ang II significantly enhanced the time-dependent reduction of mature hERG channel protein. In addition, the proteasomal inhibitor lactacystin (5 μM) inhibited Ang II-mediated the reduction of mature hERG channel protein, but the lysosomal inhibitor bafilomycin A1 (1 μM) had no effect on the protein. The protein kinase C (PKC) inhibitor bisindolylmaleimide 1 (1 μM) antagonized the reduction of mature hERG channel protein induced by Ang II. The results indicate that sustained stimulation of AT₁ receptors by Ang II reduces the mature hERG channel protein via accelerating channel proteasomal degradation involving the PKC pathway.     

Sulfadoxine-pyrimethamine impairs Plasmodium falciparum gametocyte infectivity and Anopheles mosquito survival

Sulfadoxine-pyrimethamine (SP) is currently the drug of choice for intermittent preventive treatment of Plasmodiumfalciparum both in pregnancy and infancy. A prolonged parasite clearance time conferred by dhfr and dhps mutations is believed to be responsible for increased gametocyte prevalence in SP treated individuals. However, using a direct feeding assay in Mali, we showed that gametocytes present in peripheral venous blood post-SP treatment had reduced infectivity for Anophelesgambiae sensu stricto (ss) mosquitoes. We investigated the potential mechanisms involved in the dhfr and dhps quintuple mutant NF-135 and the single dhps 437 mutant NF-54. Concentrations of sulfadoxine (S) and pyrimethamine (P) equivalent to the serum levels of the respective drugs on day 3 (S = 61 μg/ml, P = 154.7 ng/ml) day 7 (S = 33.8 μg/ml, P = 66.6 ng/ml) and day 14 (S = 14.2 μg/ml, P = 15.7 ng/ml) post-SP treatment were used to study the effect on gametocytogenesis, gametocyte maturation and infectivity to Anophelesstephensi mosquitoes fed through an artificial membrane. The drugs readily induced gametocytogenesis in the mutant NF-135 strain but effectively killed the wild-type NF-54. However, both drugs impaired gametocyte maturation yielding odd-shaped non-exflagellating mature gametocytes. The concomitant ingestion of both S and P together with gametocytemic blood-meal significantly reduced the prevalence of oocyst positivity as well as oocyst density when compared to controls (P < 0.001). In addition, day 3 concentrations of SP decreased mosquito survival by up to 65% (P < 0.001). This study demonstrates that SP is deleterious in vitro for gametocyte infectivity as well as mosquito survival.     

Kinetic mechanism and catalysis of Trypanosoma cruzi dihydroorotate dehydrogenase enzyme evaluated by isothermal titration calorimetry

Trypanosoma cruzi dihydroorotate dehydrogenase (TcDHODH) catalyzes the oxidation of l-dihydroorotate to orotate with concomitant reduction of fumarate to succinate in the de novo pyrimidine biosynthetic pathway. Based on the important need to characterize catalytic mechanism of TcDHODH, we have tailored a protocol to measure TcDHODH kinetic parameters based on isothermal titration calorimetry. Enzymatic assays lead to Michaelis-Menten curves that enable the Michaelis constant (K_M) and maximum velocity (V_max) for both of the TcDHODH substrates: dihydroorotate (K_M = 8.6 ± 2.6 μM and V_max = 4.1 ± 0.7 μM s^-1) and fumarate (K_M = 120 ± 9 μM and V_max = 6.71 ± 0.15 μM s^-1). TcDHODH activity was investigated using dimethyl sulfoxide (10%, v/v) and Triton X-100 (0.5%, v/v), which seem to facilitate the substrate binding process with a small decrease in K_M. Arrhenius plot analysis allowed the determination of thermodynamic parameters of activation for substrates and gave some insights into the enzyme mechanism. Activation entropy was the main contributor to the Gibbs free energy in the formation of the transition state. A factor that might contribute to the unfavorable entropy is the hindered access of substrates to the TcDHODH active site where a loop at its entrance regulates the open-close channel for substrate access.     

Triterpenoidal saponins of Pulsatilla koreana roots

Sixteen (1-16) triterpenoidal saponins were isolated from the roots of Pulsatilla koreana, of which four were determined as the previously unknown 23-hydroxy-3β-[(O-α-L-arabinopyranosyl)oxy]lup-20(29)-en-28-oic acid 28-O-β-D-glucopyranosyl ester (1), 23-hydroxy-3β-[(O-α-L-rhamnopyranosyl-(1 → 2)-α-L-arabinopyranosyl)oxy]lup-20(29)-en-28-oic acid 28-O-β-D-glucopyranosyl ester (2), 3β-[(O-α-L-rhamnopyranosyl-(1 → 2)-α-L-arabinopyranosyl)oxy]lup-20(29)-en-28-oic acid 28-O-β-D-glucopyranosyl-(1 → 6)-β-D-glucopyranosyl ester (3), and 3β-[(O-α-L-rhamnopyranosyl-(1 → 2)-O-[β-D-glucopyranosyl-(1 → 4)]-α-L-arabinopyranosyl)oxy]lup-20(29)-en-28-oic acid 28-O-α-L-rhamnopyranosyl-(1 → 4)-O-β-D-glucopyranosyl-(1 → 6)-β-D-glucopyranosyl ester (4), respectively, based on spectroscopic analysis. The inhibition of the lipopolysaccharide-induced nitric oxide production of sixteen isolated compounds was evaluated in RAW 264.7 cells at concentrations ranging from 1 μM to 100 μM.     

Bioaccumulation du Cd et du Zn chez les plants de tomates (Lycopersicon esculentum L.)

This work aims at evaluating the accumulation of cadmium (Cd) and zinc (Zn) (trace elements) in the organs of young tomato plants (Lycopersicon esculentum L. var. Rio Grande) and their effects on the rate of chlorophyll and enzyme activities involved in the antioxidant system: catalase (CAT), glutathion-S-transferase (GST) and peroxysase ascorbate (APX). Plants previously grown on a basic nutrient solution were undergoing treatment for 7 days, either by increasing concentrations of CdCl₂ or ZnSO₄ (0, 50, 100, 250, 500 μM) or by the combined concentrations of Cd and Zn (100/50, 100/100, 100/250, 100/500 μM). The results concerning the determination of metals in the various compartments of tomato plants as a function of increasing concentrations of Cd or Zn, suggest a greater accumulation of Cd and Zn in the roots compared to leaves. The combined treatment (Cd/Zn) interferes with the absorption of the two elements according to their concentrations in the culture medium. The presence of Zn at low concentrations (50 μM of Zn/100 μM Cd) has little influence on the accumulation of Cd in the roots and leaves, while the absorption of these two elements in the leaves increases and decreases in roots when their concentrations are equivalent (100/100 μM) compared to treatment alone. When the concentration of Zn is higher than that of Cd (500 μM of Zn/100 μM Cd) absorption of the latter is inhibited in the roots while increasing their translocation to the leaves. Meanwhile, the dosage of chlorophylls shows that they tend to decrease in a dose-dependent for both treatments (Cd or Cd/Zn), however, treatment with low concentrations of Zn (50 and 100 μM) stimulates chlorophyll synthesis. However, treatment with different concentrations of Cd seems to induce the activity of the enzymes studied (CAT, APX, GST). It is the same for treatment with different concentrations of Zn and this particularly for the highest concentrations. Finally, the combined treatment (Zn/Cd) also appears to cause enzyme inductions: CAT, APX and GST.     

Overproduction of geraniol by enhanced precursor supply in Saccharomyces cerevisiae

Monoterpene geraniol, a compound obtained from aromatic plants, has wide applications. In this study, geraniol was synthesized in Saccharomyces cerevisiae through the introduction of geraniol synthase. To increase geraniol production, the mevalonate pathway in S. cerevisiae was genetically manipulated to enhance the supply of geranyl diphosphate, a substrate used for the biosynthesis of geraniol. Identification and optimization of the key regulatory points in the mevalonate pathway in S. cerevisiae increased geraniol production to 36.04 mg L⁻¹. The results obtained revealed that the IDI1-encoded isopentenyl diphosphate isomerase is a rate-limiting enzyme in the biosynthesis of geraniol in S. cerevisiae, and overexpression of MAF1, a negative regulator in tRNA biosynthesis, is another effective method to increase geraniol production in S. cerevisiae.     

Light-dependent phosphate uptake of a submersed macrophyte Myriophyllum spicatum L.

The uptake kinetics of phosphate (Pi) by Myriophyllum spicatum was determined from adsorption and absorption under light and dark conditions. Pi uptake was light dependent and showed saturation following the Michaelis-Menten relation (in light: V = 16.91 × [Pi](1.335 + [Pi]), R² = 0.90, p < 0.001; in the dark: V = 5.13 × [Pi](0.351 + [Pi]), R² = 0.77, p < 0.001). Around 77% of the loss of Pi in the water column was absorbed into the tissue of M. spicatum, and only 23% was adsorbed on the surface of the plant shoots. Our study shows that M. spicatum shoots have a much higher affinity (in light: 3.9 μmol g⁻¹ dw h⁻¹ μM⁻¹; in the dark: 3.7 μmol g⁻¹ dw h⁻¹ μM⁻¹) and V_max (maximum uptake rate, shoot light) for Pi uptake than many other aquatic macrophytes (in light: 0.002-0.23 μmol g⁻¹ dw h⁻¹ μM⁻¹; in the dark: 0.002-0.19 μmol g⁻¹ dw h⁻¹ μM⁻¹), which may provide a competitive advantage over other macrophytes across a wide range of Pi concentrations.     

Fasciolagigantica: Parasitological and scanning electron microscopy study of the in vitro effects of ivermectin and/or artemether

Objective

To evaluate the in vitro effects of different concentrations of ivermectin and/or artemether on Fasciolagigantica worms and to study the parasitological changes and tegumental alterations using scanning electron microscopy (SEM).

Methods

Fasciola gigantica worms were incubated in vitro for 24 and 48 h with three concentrations of either ivermectin or artemether (10, 20 and 50 μg/ml) or both in half concentration of either (5, 10 and 25 μg/ml).

Results

Exposure of Fasciola worms to 25 + 25 μg/ml of combined drug regimens or to 50 μg/ml of either ivermectin or artemether for 48 h led to 100%, 41.7% and 75% worm killing which were accompanied by a significant reduction in egg laying capacity and significant increase in dead eggs maximally recorded in combined drug regimens. SEM of the flukes incubated for 48 h with combined drug regimens showed maximal tegumental disruption with swelling of the worm body, roughness, blebbing, sloughing and complete loss of spines. Disruption to the tegument of the flukes induced by artemether was more than that of ivermectin.

Conclusions

Artemether alone or combined with ivermectin in half doses had potent fasciocidal activities. Besides, half doses of combined drug regimens had higher ovicidal effects than each drug alone. In vivo studies are recommended to explore the efficacy of combined regimens against Fasciola infection.     

Molecular characterization and localization of Plasmodium falciparum choline kinase

Generation of phosphocholine by choline kinase is important for phosphatidylcholine biosynthesis via Kennedy pathway and phosphatidylcholine biosynthesis is essential for intraerythrocytic growth of malaria parasite. A putative gene (Gene ID PF14_0020) in chromosome 14, having highest sequence homology with choline kinase, has been identified by BLAST searches from P. falciparum genome sequence database. This gene has been PCR amplified, cloned, over-expressed and characterized. Choline kinase activity of the recombinant protein (PfCK) was validated as it catalyzed the formation of phosphocholine from choline in presence of ATP. The K_m values for choline and ATP are found to be 145 ± 20 μM and 2.5 ± 0.3 mM, respectively. PfCK can phosphorylate choline efficiently but not ethanolamine. Southern blotting indicates that PfCK is a single copy gene and it is a cytosolic protein as evidenced by Western immunoblotting and confocal microscopy. A model structure of PfCK was constructed based on the crystal structure of choline kinase of C. elegans to search the structural homology. Consistent with the homology modeling predictions, CD analysis indicates that the α and β content of PfCK are 33% and 14%, respectively. Since choline kinase plays a vital role for growth and multiplication of P. falciparum during intraerythrocytic stages, we can suggest that this well characterized PfCK may be exploited in the screening of new choline kinase inhibitors to evaluate their antimalarial activity.     

First report of an anti-tumor, anti-fungal, anti-yeast and anti-bacterial hemolysin from Albizia lebbeck seeds

A monomeric 5.5-kDa protein with hemolytic activity toward rabbit erythrocytes was isolated from seeds of Albizia lebbeck by using a protocol that involved ion-exchange chromatography on Q-Sepharose and SP-Sepharose, hydrophobic interaction chromatography on Phenyl-Sepharose, and gel filtration on Superdex 75. It was unadsorbed on both Q-Sepharose and SP-Sepharose, but adsorbed on Phenyl-Sepharose. Its hemolytic activity was fully preserved in the pH range 0-14 and in the temperature range 0-100 °C, and unaffected in the presence of a variety of metal ions and carbohydrates. The hemolysin reduced viability of murine splenocytes and inhibited proliferation of MCF-7 breast cancer cells and HepG2 hepatoma cells with an IC₅₀ of 0.21, 0.97, and 1.37 μM, respectively. It impeded mycelial growth in the fungi Rhizoctonia solani with an IC₅₀ of 39 μM but there was no effect on a variety of other filamentous fungi, including Fusarium oxysporum, Helminthosporium maydis, Valsa mali and Mycosphaerella arachidicola. Lebbeckalysin inhibited growth of Escherichia coli with an IC₅₀ of 0.52 μM.     

Botryorhodines A-D, antifungal and cytotoxic depsidones from Botryosphaeria rhodina, an endophyte of the medicinal plant Bidens pilosa

An endophytic fungus (Botryosphaeria rhodina) was isolated from the stems of the medicinal plant Bidens pilosa (Asteraceae) that is known for its anti-inflammatory, antiseptic and antifungal effects. The ethyl acetate extract of the fungal isolate exhibits significant antifungal activity as well as potent cytotoxic and antiproliferative effects against several cancer cell lines. Activity-guided fractionation resulted in the isolation of a complex of four depsidones, botryorhodines A-D and the auxin indole carboxylic acid. Botryorhodine A and B show moderate to weak cytotoxic activities against HeLa cell lines with a CC₅₀ of 96.97 μM and 36.41 μM, respectively. In addition, they also show antifungal activity against a range of pathogenic fungi such as Aspergillus terreus (MIC 26.03 μM for botryorhodine A and 49.70 μM for B) and the plant pathogen Fusarium oxysporum (MIC 191.60 μM for botryorhodine A and 238.80 μM for B). A potential role of the endophyte in modulating fungal populations living within or attacking the host plant is discussed.     

Chemical profile of the North American native Myriophyllum sibiricum compared to the invasive M. spicatum

Myriophyllum spicatum L. is a nonindigenous invasive plant in North America that can displace the closely related native Myriophyllum sibiricum Komarov. We analyzed the chemical composition (including: C, N, P, polyphenols, lignin, nonpolar extractables, and sugars) of M. spicatum and M. sibiricum and determined how the chemistry of the two species varied by plant part with growing environment (lake versus tank), irradiance (full sun versus 50% shading), and season (July through September). M. spicatum had higher concentrations of carbon, polyphenols and lignin (C: 47%; polyphenols: 5.5%; lignin: 18%) than M. sibiricum (C: 42%; polyphenols: 3.7%; lignin: 9%) while M. sibiricum had a higher concentration of ash under all conditions (12% versus 8% for M. spicatum). Apical meristems of both species had the highest concentration of carbon, polyphenols, and tellimagrandin II, followed by leaves and stems. Tellimagrandin II was present in apical meristems of both M. spicatum (24.6 mg g⁻¹ dm) and M. sibiricum (11.1 mg g⁻¹ dm). Variation in irradiance from 490 (shade) to 940 (sun) μmol of photons m⁻² s⁻¹ had no effect on C, N, and polyphenol concentrations, suggesting that light levels above 490 μmol of photons m⁻² s⁻¹ do not alter chemical composition. The higher concentration of polyphenols and lignin in M. spicatum relative to M. sibiricum may provide advantages that facilitate invasion and displacement of native plants.     

Pomolic acid of Licania pittieri elicits endothelium-dependent relaxation in rat aortic rings

Pomolic acid has recently shown hypotensive effect in rats. The purpose of this investigation was to determine the vascular effects of this triterpenoid and to examine its mode of action. Functional experiments in rat aortic rings precontracted with norepinephrine were performed to evaluate the vasorelaxant effect of pomolic acid. This triterpenoid induced a vasorelaxation (IC₅₀ = 2.45 μM) in a concentration- and endothelium-dependent manner and showed no effect on contractions evoked by KCl (25 mM). Pre-treatment of aortic rings with l-NAME (100 μM), methylene blue (100 μM) or glibenclamide (10 μM), totally prevented the vasorelaxation induced by pomolic acid, while indomethacin (10 μM) had no effect on this response. Additionally, pomolic acid relaxation was unaffected under the muscarinic- and β-adrenergic-receptor blocked ensured for atropine and propanolol respectively (10 μM each). In contrast, the vasorelaxant effect of pomolic acid was abolished under the purinergic-receptor blocked ensured for suramin (10 μM). Finally, apyrase (0.8 U/ml) an enzyme which hydrolyses ATP and ADP did not affect pomolic acid relaxation. In summary, pomolic acid has a potent endothelium-dependent vasorelaxant effect, possibly acting through the direct activation of endothelial purinergic receptors via NO-cGMP signaling pathway, which could be part of the mechanism underlying its hypotensive effect.