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PubMed1998

High-performance liquid chromatographic analysis of polyhydroxyflavones using solid-phase borate-complex extraction.

A high-performance liquid chromatographic method using a solid-phase borate-complex extraction pretreatment was studied for the selective quantitation of polyhydroxyflavones in vegetables, red wine and human blood plasma. Homogenate, extract and intact samples were applied to phenylboric acid cartridges to retain polyhydroxyflavones on the solid-phase by forming the borate-complex, followed by elution of the retained analytes with an acidic solvent. Reversed-phase chromatography with diode array detection allowed the simultaneous separation of rutin, myricetin, fisetin, morin, quercetin and kaempferol without significant interference from other components, indicating high selectivity of the solid-phase borate-complex extraction. The absolute recoveries of quercetin, fisetin and rutin were superior to those of kaempferol, myricetin and morin, suggesting a difference in the complex formation efficiency between 1,2- and 1,3-diol structures. When using fisetin as an internal standard, polyhydroxyflavones were quantified in the concentration range 0.10-30.0 microg/ml. In replicate spiking experiments with standards, the mean relative recoveries ranged between 75.7 and 104.6%, and the intra-and inter-assay C.V.s ranged between 0.8 and 10.2% for onion, wine and plasma samples. The proposed method will be applicable to nutritional and pharmacokinetic experiments of polyhydroxyflavones.

Chromatography, High Pressure Liquid↗

PubMed2003

Free radical scavenging abilities of flavonoids as mechanism of protection against mutagenicity induced by tert-butyl hydroperoxide or cumene hydroperoxide in Salmonella typhimurium TA102.

Mutagenicity induced by tert-butyl hydroperoxide (BHP) or cumene hydroperoxide (CHP) in Salmonella typhimurium TA102 was effectively reduced by flavonols with 3',4'-hydroxyl groups such as fisetin, quercetin, rutin, isoquercitrin, hyperoxide, myricetin, myricitrin, robinetin, and to a lesser extent also by morin and kaempferol (ID50=0.25-1.05 micromol per plate). With the exception of isorhamnetin, rhamnetin, morin, and kaempferol, closely similar results were obtained with both peroxides. Hydrogenation of the double bond between carbons 2 and 3 (dihydroquercetin, dihydrorobinetin) as well as the additional elimination of the carbonyl function at carbon 4 (catechins) resulted in a loss of antimutagenicity with the notable exception of catechin itself. Again, all flavones and flavanones tested were inactive except luteolin, luteolin-7-glucoside, diosmetin, and naringenin. The typical radical scavenger butylated hydroxytoluene also showed strong antimutagenicity against CHP (ID50=5.4 micromol per plate) and BHP (ID50=11.4 micromol per plate). Other lipophilic scavengers such as alpha-tocopherol and N,N'-diphenyl-1,4-phenylenediamine exerted only moderate effects, the hydrophilic scavenger trolox was inactive. The metal chelating agent 1,10-phenanthroline strongly reduced mutagenicities induced by CHP and BHP (ID50=2.75 and 2.5 micromol per plate) at low concentrations but induced mutagenic activities at higher concentrations. The iron chelator deferoxamine mesylate, however, was less effective in both respects. The copper chelator neocuproine effectively inhibited mutagenicity induced by BHP (ID50=39.7 micromol per plate) and CHP (ID50=25.9 micrommol per plate), the iron chelator 2,2'-dipyridyl was less potent (ID50=6.25 mmol per plate against BHP, 0.42 mmol per plate against CHP). In the absence of BHP and CHP, yet not in the presence of these hydroperoxides, quercetin, rutin, catechin, epicatechin, and naringenin induced strong mutagenic activities in S. typhimurium TA102. Radical scavenging activities of flavonoids against peroxyl radicals generated from 2,2'-azo-bis(2-amidinopropane)dihydrochloride (AAPH) as measured in the haemolysis test, confirmed that in general flavonoids with di- or trihydroxy hydroxyl functions especially in positions 3', 4', 5' are effective radical scavengers. In this test system, however, luteolin was the most potent compound, followed by epicatechin and eriodictyol. Again, isorhamnetin was a potent inhibitor of lysis of red blood cells despite the presence of a 3'-OCH3 function. Radical scavenging activities of flavonoids against the stable radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) in principle obeyed the rules outlined above. Flavanones, tamarixetin, and rhamnetin, however, were only weakly active against DPPH, while isorhamnetin was again a potent compound. From these results we conclude that in the Salmonella/reversion assay with strain TA102 antimutagenic activities of flavonoids against the peroxide mutagens CHP and BHP are mainly caused by radical scavenging effects.

Antimutagenic Agents↗

PubMed2003

High-performance liquid chromatographic determination of quercetin in human plasma and urine utilizing solid-phase extraction and ultraviolet detection.

An HPLC method for determining quercetin in human plasma and urine is presented for application to the pharmacokinetic study of rutin. Isocratic reversed-phase HPLC was employed for the quantitative analysis by using kaempferol as an internal standard. Solid-phase extraction was performed on an Oasis HLB cartridge (>95% recovery). The HPLC assay was carried out using a Luna ODS-2 column (150 x 2.1 mm I.D., 5 microm particle size). The mobile phase was acetonitrile-10 mM ammonium acetate solution containing 0.3 mM EDTA-glacial acetic acid, 29:70:1 (v/v, pH 3.9) and 26:73:1 (v/v, pH 3.9) for the determination of plasma and urinary quercetin, respectively. The flow-rate was 0.3 ml/min and the detection wavelength was set at 370 nm. Calibration of the overall analytical procedure gave a linear signal (r>0.999) over a concentration range of 4-700 ng/ml of quercetin in plasma and 20-1000 ng/ml of quercetin in urine. The lower limit of quantification was approximately 7 ng/ml of quercetin in plasma and approximately 35 ng/ml in urine. The detection limit (defined at a signal-to-noise ratio of about 3) was approximately 0.35 ng/ml in plasma and urine. A preliminary experiment to investigate the plasma concentration and urinary excretion of quercetin after oral administration of 200 mg of rutin to a healthy volunteer demonstrated that the present method was suitable for determining quercetin in human plasma and urine.

Chromatography, High Pressure Liquid↗

PubMed2003

Structural characterization and detection of kale flavonoids by electrospray ionization mass spectrometry.

Sensitive and precise analytical methods are needed for flavonols, a subclass of flavonoids that has strong antioxidant activity. We report an improved method for identifying the predominant flavonols, quercetin and kaempferol, by collisionally activated dissociation (CAD) and quantifying them by high-performance liquid chromatography electrospray ionization mass spectrometry (HPLC-ESI-MS) in the selected ion monitoring mode. Practical applications of the method were demonstrated using several kale and biological samples. Two commercial kale samples were found to have 77 or 244 ppm quercetin and 235 or 347 ppm kaempferol (ppm = microg of quercetin/g of kale or microg of kaempferol/g of kale by fresh weight, 5-15% relative standard deviation). Blanching was found to reduce the flavonols to approximately 60% of the levels found in the unblanched kale. Isotopically labeled kale (cultivar Vates) grown in a greenhouse under an atmosphere of (13)CO(2) was found to have much lower flavonol levels. UV-A and UV-B supplementation during kale growth in the greenhouse was found to enhance both quercetin and kaempferol levels in Vates kale. The UV-B-supplemented kale not only produced more flavonols but the quercetin-to-kaempferol ratio was also higher than the UV-A-supplemented or the nonsupplemented kale. Recovery of flavonols from kale was approximately 60% based on spike and recovery trials with rutin, a glycoside of quercetin. Recovery of flavonols from biological samples spiked with rutin ranged from 96% for urine to 70% for plasma. Compared to UV detection, ESI-MS in the deprotonation mode provided lower detection limits, and both higher sensitivity and selectivity, in addition to structural characterization of the kale flavonols by CAD.

Brassica↗

PubMed2000

Potential nitrite scavengers as inhibitors of the formation of N-nitrosamines in solution and tobacco matrix systems.

The ability of 20 compounds, all but one tobacco constituents, to inhibit the formation of tobacco-specific N-nitrosamines (TSNA) was investigated in buffer and detergent solution and in tobacco midrib and lamina systems. In solution at pH 5.5, ascorbic acid and the phenolic acids caffeic and ferulic acid were the most potent inhibitors of the reaction between nornicotine and nitrite, with nearly complete inhibition at molar ratios test compound/nitrite > 1:1. Also, cysteine > dihydrocaffeic acid > protocatechuic acid approximately catechin acted as strong inhibitors with >90% inhibition at a ratio of 3:1. Lower inhibitions were observed with chlorogenic acid > p-coumaric acid > sclareol > serine. Rutin showed an inhibition of 34% at a ratio of 0.1:1. Sclareol, alanine, proline, and serine did not significantly affect the N-nitrosonornicotine (NNN) formation. alpha-Tocopherol and glutathione enhanced NNN formation at pH 5.5 but were inhibitors at pH 3. Cinnamic acid, vanillic acid, eugenol, and esculin enhanced NNN formation. Increased NNN formation was also observed for dihydrocaffeic acid, chlorogenic acid, protocatechuic acid, and catechin at a less-than-equimolar ratio of test compound to nitrite. The tobacco matrix experiments were performed with air-cured, ground tobacco midrib and lamina. Caffeic acid, ferulic acid, dihydrocaffeic acid and catechin were potent inhibitors of the formation of TSNA in the midrib as well as in the lamina. Also protocatechuic acid, glutathione, ascorbic acid, p-coumaric acid, chlorogenic acid and cysteine were inhibitors, while alpha-tocopherol and rutin inhibited the reaction in the midrib but not in the lamina. Cinnamic acid, vanillic acid, eugenol, alanine, proline and serine showed small effects only. The molar ratio of secondary alkaloid(s)/nitrite in the test systems were 0.1:1 (solution), approximately 0.25:1 (midrib), and approximately 1:1 (lamina) and is most likely the major contributor to the observed order of inhibition potency (solution > midrib > lamina) of the test compounds. The vicinal phenolic hydroxyl groups of polyphenols and the simultaneous presence of a phenol group and an olefinic bond in hydroxycinnamic acids were the most characteristic structural elements of the potent inhibitors.

Free Radical Scavengers↗

PubMed2001

Monoamine oxidase B and free radical scavenging activities of natural flavonoids in Melastoma candidum D. Don.

Monoamine oxidase type B (MAO-B) activity and free radicals are elevated in certain neurological diseases. Four natural flavonoids, quercitrin, isoquercitrin, rutin, and quercetin, were isolated for the first time from the leaves of Melastoma candidum D. Don. They exhibited an inhibitory effect on MAO-B. These potent flavonoids were purified using bioassay-guided fractionation and were separated by Diaion, Sephadex LH-20, and MCI CHP20P columns. The IC(50) values of the four potent flavonoids, quercitrin, isoquercitrin, rutin, and quercetin on monoamine oxidase were 19.06, 11.64, 3.89, and 10.89 microM and enzyme kinetics analysis revealed apparent inhibition constants (K(i)) of 21.01, 2.72, 1.83, and 7.95 microM, respectively, on the substrate, benzylamine. The four potent compounds also exhibited hydroxyl radical scavenging activity as determined using a spin trapping electron spin resonance method. This suggests that the four flavonoids from M. candidum possess both MAO-B inhibitory and free radical scavenging activities. These important properties may be used for preventing some neurodegenerative diseases in the future.

Chromatography, High Pressure Liquid↗

PubMed2004

Synthesis of antioxidants in wheat sprouts.

Aqueous and ethanolic extracts from wheat (Triticum aestivum) sprout powder were analyzed to determine its reduction and antioxidant activities. Mean and standard deviation of five independent samples were reported. The results showed that the micromoles of potassium ferricyanide reduced by aqueous and ethanolic extracts corresponding to 1 g of sprout powder (80.6 +/- 11.2 and 9.7 +/- 1.8, respectively) were higher than that reduced by 1 mg of other reducing compounds: ascorbic acid, rutin, quercetin, and reduced gluthatione (4.8 +/- 0.7, 3.8 +/- 1.2, 4.8 +/- 1.7, and 1.6 +/- 0.4, respectively). In addition, the oxygen superoxide scavenging activity performed by sprout extracts (from 1 g of powder) is comparable to that shown by 10 mg of antioxidant pure compounds (rutin and quercetin). Biochemical analysis of the sprout extracts shows that the antioxidant activity is mainly due to reducing glycoside and polyphenolic compounds.

Antioxidants↗

PubMed2005

Effect of copigments and grape cultivar on the color of red wines fermented after the addition of copigments.

The prefermentation addition of copigments led to significantly different red wines according to the copigment structure (flavonol or hydroxycinnamic acid) and the grape cultivar [Tempranillo (= Cencibel) or Cabernet Sauvignon]. The flavonol rutin enhanced copigmentation and anthocyanin extraction, improving the red color, but the hydroxycinnamic acids (especially caffeic acid) had converse results. The above effects were higher in Cabernet Sauvignon wines, particularly if rutin or p-coumaric acid was used. These wines showed the highest copigmentation as they contained more anthocyanins and flavonols, whereas the coumaroylated anthocyanins of Tempranillo wines could have prevented the action of the added copigments. After 21 months, the main pyranoanthocyanins found were the malvidin-3-glucoside 4-vinylphenol and the malvidin-3-glucoside 4-vinylcatechol (pinotin A) adducts. The results suggested that the former adduct was primarily generated following enzymatic decarboxylation of p-coumaric acid during fermentation, whereas pinotin A was formed through a pure chemical reaction, which depended on the concentration of free caffeic acid during aging.

Anthocyanins↗

PubMed2006

Cytochrome P450 1A1 expression and activity in Caco-2 cells: modulation by apple juice extract and certain apple polyphenols.

Cytochrome P450 (CYP) 1A1 plays a role in drug metabolism of intestinal cells (e.g., by activating certain chemical carcinogens such as polycyclic aromatic hydrocarbons into carcinogenic metabolites). In the human colon carcinoma cell line Caco-2, we investigated the effects of a defined polyphenolic apple juice extract (AJE), the major principle flavonoid/dihydrochalkone constituents quercetin and phloretin, and the corresponding prototype glycosides rutin and phlorizin on CYP1A1 expression and activity. Incubations were carried out with or without the potent aryl hydrocarbon receptor agonist/CYP1A1 inducer 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). AJE and quercetin acted as weak inducers of CYP1A1 mRNA and protein, and AJE, quercetin, and phlorizin led to a slight induction of CYP1A1-catalyzed 7-ethoxyresorufin O-deethylase (EROD) activity. However, AJE, quercetin, and phloretin were highly effective in suppressing CYP1A1 induction in co-incubations of the cells with 1 nM TCDD. The antagonistic effects were seen on the levels of mRNA, enzyme protein, and catalytic activity. In contrast, the related glycosides rutin and phlorizin were inactive as inducers or inhibitors. Inhibition of CYP1A1 induction was not related to general cytotoxicity, which could be completely abolished by the addition of ascorbic acid/alpha-tocopherol. AJE, quercetin, and phloretin also antagonized the TCDD-mediated induction of a reporter gene driven by a regulatory sequence of the human CYP1A1 gene promoter. Our findings suggest that apple juice extract can antagonize TCDD-mediated CYP1A1 induction by interfering with AhR-dependent gene transcription and by inhibiting the catalytic activity of CYP1A1. These effects may result in reduced metabolic activation of certain chemical carcinogens, in particular, under conditions of sustained AhR activation.

Beverages↗

PubMed1999

Effect of processing on the flavonoid content in buckwheat (Fagopyrum esculentum Möench) grain.

Six flavonoids have been isolated and identified in buckwheat grain. These are rutin, orientin, vitexin, quercetin, isovitexin, and isoorientin. Rutin and isovitexin are the only flavonoid components of buckwheat seeds while hulls contain all six identified compounds. The total flavonoid concentration in the seeds was 18.8 and in the hulls 74 mg/100 g of dry matter. Dehulling the grain by using different temperature regimes resulted in drastic reductions of the total flavonoid concentration in the grain (by 75% of the control) and smaller but significant (15-20%) reduction in the hulls.

Chromatography, High Pressure Liquid↗

PubMed2000

Effect of pH on the stability of plant phenolic compounds.

It is not uncommon to treat plant-derived foods and feeds with alkali. Such exposure to high pH is being used to recover proteins from cereals and legumes, to induce the formation of fiber-forming meat analogue vegetable protein, for preparing peeled fruits and vegetables, and for destroying microorganisms. In addition to their profound effects on functional and nutritional properties in such foods, such treatments may also cause other side reactions, including the destruction of natural polyphenolic compounds. Because plants contain a large number of structurally different antioxidant, anticarcinogenic, and antimicrobial polyphenolic compounds, it is of interest to know whether such compounds are stable to heat and to high pH. In this model study, the stability of the following natural polyphenols to pH in the range 3-11 was studied with the aid of ultraviolet spectroscopy: caffeic acid, (-)-catechin, chlorogenic acid, ferulic acid, gallic acid, (-)-epigallocatechin, rutin, and the nonphenolic compound trans-cinnamic acid. This study demonstrates that caffeic, chlorogenic, and gallic acids are not stable to high pH and that the pH- and time-dependent spectral transformations are not reversible. By contrast, chlorogenic acid is stable to acid pH, to heat, and to storage when added to apple juice. (-)-Catechin, (-)-epigallocatechin, ferulic acid, rutin, and trans-cinnamic acid resisted major pH-induced degradation. The results are rationalized in terms of relative resonance stabilization of phenoxide ions and quinone oxidation intermediates. The possible significance of these findings to food chemistry and microbiology is discussed.

Drug Stability↗

PubMed2000

Antioxidant activity and radioprotective effects against chromosomal damage induced in vivo by X-rays of flavan-3-ols (Procyanidins) from grape seeds (Vitis vinifera): comparative study versus other phenolic and organic compounds.

The quantitative distribution of several flavan-3-ols was determined using HPLC in a grape (Vitis vinifera) seed extract (GSE) of four cultivars grown in the region of Murcia. Polymer >/= C(4) units made up the largest group of procyanidins in the GSE (90.92%, expressed as HPLC % area). The antioxidant activity of GSE and other reference compounds was investigated by measuring their ability to scavenge the ABTS(*)(+) radical cation (TEAC). The most effective compounds were, in order: GSE > rutin > (+)-catechin > diosmin >/= ascorbic acid. The radioprotective effects of GSE and other reference compounds were determined by using the micronucleus test for anticlastogenic activity, any reduction of the frequency of micronucleated polychromatic erythrocytes (MnPCEs) being evaluated in the bone marrow of mouse exposed to X-rays. The most effective compounds were, in order: GSE > rutin > dimethyl sulfoxide (DMSO) > ascorbic acid > 6-n-propyl-2-thiouracil-6c (PTU) > diosmin. The higher ABTS(*)(+) scavenging capacity and anticlastogenic activity of GSE can be explained, structurally, by the high number of conjugated structures between the catechol groups in the B-rings and the 3-OH free groups of the polymeric polyphenolic skeleton and, in addition, by the stability of the aroxyl flavonoid radical generated in the above processes.

Animals↗

PubMed2005

Kinetic study of the quenching reaction of singlet oxygen by flavonoids in ethanol solution.

The quenching rate of singlet oxygen (1O2) by seven kinds of flavonoids (flavone, flavonol, chrysin, apigenin, rutin, quercetin, and myricetin) with 2,3-double bonds has been measured spectrophotometrically in ethanol at 35 degrees C. The overall rate constants kQ (= kq + kr, physical quenching + chemical reaction) increased as the number of OH groups substituted to the flavone skeleton (that is, the total electron-donating capacity of flavonoids) increases. The existence of catechol or pyrogallol structure in the B-ring is essential for the 1O2 quenching of flavonoids. Log kQ was found to correlate with their peak oxidation potentials, E(P); the flavonoids that have smaller E(P) values show higher reactivities. Similarly, log kQ values of flavonoids correlate with the energy level of the highest occupied molecular orbital (E(HOMO)), calculated by the PM3 MO method, and the longest wavelength pi pi* excitation energy (E(ex)). The contribution of the chemical reaction (kr) was found to be negligible in these flavonoids. The kQ values of rutin, quercetin, and myricetin [(1.21 approximately 5.12) x 10(8) M(-1) s(-1)] were found to be larger than those of lipids [(0.9 approximately 6.4) x 10(4) M(-1) s(-1)], amino acids (<3.7 x 10(7) M(-1) s(-1)), and DNA (5.1 x 10(5) M(-1) s(-1)). The result suggests that these flavonoids may contribute to the protection of oxidative damage in foods and plants, by quenching 1O2.

Ethanol↗

PubMed2003

Comparative study of antioxidant properties and cytoprotective activity of flavonoids.

Antioxidant properties and cytoprotective activity of flavonoids (rutin, dihydroquercetin, quercetin, epigallocatechin gallate (EGCG), epicatechin gallate (ECG)) were studied. All these compounds inhibited both NADPH- and CCl4-dependent microsomal lipid peroxidation, and the catechins were the most effective antioxidants. The I(50) values calculated for these compounds by regression analysis were close to the I(50) value of the standard synthetic antioxidant ionol (2,6-di-tert-butyl-4-methylphenol). The antiradical activity of flavonoids to O2-* was studied in a model photochemical system. Rate constants of the second order reaction obtained by competitive kinetics suggested flavonoids to be more effective scavengers of oxygen anion-radicals than ascorbic acid. By competitive replacement all flavonoids studied were shown to be chelating agents capable of producing stable complexes with transition metal ions (Fe2+, Fe3+, Cu2+). The flavonoids protected macrophages from asbestos-induced damage, and the protective effect increased in the following series: rutin < dihydroquercetin < quercetin < ECG < EGCG. The cytoprotective effect of flavonoids was in strong positive correlation with their antiradical activity to O2-*.

Animals↗

PubMed2004

Regioselective acylation of flavonoids catalyzed by immobilized Candida antarctica lipase under reduced pressure.

A single-step acylation of rutin and naringin, catalyzed by immobilized Candida antarctica lipase B in 2-methyl-2-butanol, occurred preferentially on the primary hydroxyl group. Using palmitic methyl ester as acyl donor, the acylation rate of naringin was 10-fold higher than that of rutin. Under optimal conditions, i.e. a molar ratio acyl donor/naringin of 7:1 and 200 mbar, 92% naringin was acylated.

Acylation↗

PubMed1990

Inhibitory effect of quercetin on OVCA 433 cells and presence of type II oestrogen binding sites in primary ovarian tumours and cultured cells.

We investigated the effect of the flavonoid quercetin (Q) on the proliferation of the ovarian cancer cell line OVCA 433. Growth experiments demonstrated that Q exerted a reversible dose-dependent inhibition of cell proliferation in the range of concentrations between 10 nM and 10 microM. Two other flavonoids tested, rutin and hesperidin, were ineffective in inhibiting cell growth. Cell cycle analysis showed that the growth inhibitory effect of Q was due to a blocking effect in the GO/G1 phase. Using a whole cell assay with (6.7-3H) oestradiol (3H-E2) as tracer we demonstrated that OVCA 433 cells contain type II oestrogen binding sites (type II EBS). Competition analysis showed that Q competed for 3H-E2 binding to type II EBS while both rutin and hesperidin did not. Appreciable amounts of type II EBS were also detected in seven primary ovarian tumours. Our results suggest that Q may regulate ovarian cancer cell growth through a mechanism involving a binding interaction with type II EBS. This mechanism could also be active in vivo since primary ovarian tumours contain type II EBS.

Cell Division↗

PubMed2003

Nitric oxide produced by a novel nitric oxide synthase isoform is necessary for gonadotropin-releasing hormone-induced growth hormone secretion via a cGMP-dependent mechanism.

The involvement of nitric oxide (NO) in the regulation of goldfish growth hormone (GH) secretion was further characterized using primary cultures of dispersed goldfish pituitary cells. Western blots revealed the presence of an inducible nitric oxide synthase (iNOS)-like protein of approximately 120 kDa in cytosol/plasma membrane extracts. By contrast, brain NOS-immunoreactive proteins of approximately 120-140 kDa were occasionally detected in a cytoskeleton/organelle fraction but were absent from cytosol/plasma membrane extracts. The NO donor sodium nitroprusside (SNP) acutely increased GH secretion but this response was not observed in the presence of either a NO scavenger (PTIO) or a soluble guanylate cyclase inhibitor (ODQ). SNP also significantly increased the levels of cyclic (c)GMP in somatotrope-enriched cell populations. Treatments with 1400W (iNOS inhibitor), PTIO and rutin hydrate (NO scavengers) and ODQ abolished the acute GH-release response to two endogenous gonadotropin-releasing hormones (GnRH). 1400W, rutin hydrate, PTIO and ODQ alone did not significantly alter basal GH secretion. Together, these results establish that an iNOS-like peptide is constitutively present in the pituitary of the goldfish. Furthermore, these data suggest that NO, most likely through the generation of cGMP, is a necessary signal transduction component of GnRH-induced GH secretion.

Animals↗

PubMed2003

Effect of acute drought stress and time of harvest on phytochemistry and dry weight of St. John's wort leaves and flowers.

The phytochemistry and dry weight of cultivated St. John's wort are significantly influenced by acute drought stress and time of harvest. In this study, plants subjected to brief drought stress during both flower and seed development periods exhibited increased concentrations in 8 of the 10 phytochemicals examined in this study, including hypericin, pseudohypericin, chlorogenic acid, rutin, hyperoside, isoquercitrin, quercitrin, and quercetin. Increases ranged from 5% to 36% (hyperoside and rutin, respectively). Conversely, the concentrations of hyperforin and adhyperforin in flowers were decreased by an average of 10% in drought-stressed plants as compared to well-watered control plants. Acute drought stress decreased flower dry weight significantly during both drydown periods, although vegetative parameters (height, leaf dry weight and stem dry weight) were not adversely affected. While acute drought stress significantly altered the chemical yield in the leaves and flowers (phytochemical content x harvested dry weight), the time of harvest was the predominant factor determining phytochemical concentration in the organs of H. perforatum.

Adaptation, Physiological↗