The effect of a moderately thermoxidized dietary fat on the vitamin E status,the fatty acid composition of tissue lipids,and the susceptibility of low-density lipoproteins to lipid peroxidation in rats

Several studies demonstrated that dietary oxidized oils markedly affect the vitamin E status and alter the fatty acid composition of tissue lipids in animals. It must however be emphasized that highly oxidized oils reduce the feed intake of animals, which makes it difficult to interpret the results. Therefore, the present study used a moderately thermoxidized soybean oil (peroxide value: 75 mEq O₂/kg), having a similar fatty acid composition as fresh soybean oil (peroxide value: 9.5 mEq O₂/kg) which was used as control. Moreover, according to a bifactorial design, two different vitamin E supplementary levels (11 vs. 511 mg α-to-copherol equivalents per kg diet) were used. The experiment was conducted with male Sprague-Dawley rats. The feeding period lasted for 40 days. In order to assess the vitamin E status, the vitamin E concentrations in plasma, liver, heart, kidney, and adipose tissue were determined. The vitamin E supply had a pronounced effect on the vitamin E concentrations of those tissues whereas the type of fat had only a slight effect. The fatty acid composition of total lipids from liver, erythrocytes, and low-density lipoproteins was also only slightly influenced by the oxidized fat. The osmotic fragility of erythrocytes was even reduced by feeding the oxidized oil. With a low vitamin E supply, the in vitro susceptibility of low-density lipoproteins to lipid peroxidation was slightly increased by feeding the oxidized oil. In contrast, with a high vitamin E supply, there was no adverse effect of the dietary oxidized oil on the susceptibility of low-density lipoproteins to lipid peroxidation. Feeding the oxidized oil, however, increased the concentrations of malondialdehyde in low-density lipoproteins suggesting an increased in vivo lipid peroxidation. Therefore, it cannot be ruled out that moderately oxidized dietary fats increase the atherogenicity of low-density lipoproteins. In contrast, a moderately oxidized oil scarcely affected the vitamin E status and the fatty acid composition of tissue lipids.     

The influence of vitamin E and selenium on lipid peroxidation and aldehyde dehydrogenase activity in rat liver and tissue

Malondialdehyde (MDA) production and cytosolic aldehyde dehydrogenase (ALDH) response were examined in rat liver tissues after feeding different levels of dietary vitamin E and/or selenium and polyunsaturated fat for 12–38 wk. MDA production was significantly increased by vitamin E deficiency or by high levels of polyunsaturated fat intake, but not by selenium deficiency. The activity of cytosolic ALDH increased upon increased production of MDA after 12–16 wk of feeding the lipid peroxidation-inducing diets. However, ALDH activity was suppressed after 38 wk of feeding the vitamin E-deficient diet. The results indicate that the hepatic cytosolic ALDH may be involved in the metabolism of MDA during a relatively short-term increase inin vivo lipid peroxidation, but that ALDH activity becomes suppressed after more severein vivo lipid peroxidation has been produced. Hepatic and plasma α-tocopherol levels and lipid peroxidation products were measured for the various dietary groups.     

The effect of linoleic,arachidonic and eicosapentaenoic acid supplementation on prostacyclin production in rats

We examined the effect of dietary supplementation of linoleic acid (LA), arachidonic acid (AA) or eicosapentaenoic acid (EPA) to rats fed a diet low in linoleic acid onin vitro andin vivo production of prostacyclin. Male Sprague Dawley rats were fed a high-fat diet (50% energy as fat, 1.5% linoleic acid) for two weeks. Three of the groups were then supplemented orally with either 90 mg/d of LA, AA or EPA, all as the ethyl esters, for a further two weeks while remaining on the high-fat diet. Forty-eight hour urine samples were collected at the end of the second and fourth weeks.In vivo prostacyclin production was determined by a stable isotope dilution, gas chromatography/mass spectrometry assay for the major urinary metabolite of prostacyclins (2,3-dinor-6-keto-PGF_1α or PGI₂-M and Δ¹⁷-2-3-dinor-6-keto-PGF_1α or PGI₃-M).In vitro prostacyclin production was determined by radioimmunoassay of the stable metabolite (6-keto-PGF_1α) following incubation of arterial tissue. Oral supplementation with AA resulted in a rise in plasma and aorta 20∶4n−6, and increasedin vitro prostacyclin and urinary PGI₂-M production. EPA supplementation resulted in a rise in plasma and aorta 20∶5n−3 and 22∶5n−3, and a decline in plasma 20∶4n−6, but not in the aorta. In the EPA-supplemented group, thein vitro prostacyclin and the urinary PGI₃-M increased, but urinary PGI₂-M decreased. The increase inin vitro prostacyclin production in the EPA-supplemented rats was unexpected and without obvious explanation. Supplementation with LA had minimal effect on fatty acid composition of plasma or aorta and caused no change in prostacyclin production with either method. Thein vivo measure of prostacyclin production was positively correlated with aorta AA levels, and negatively correlated with aorta levels of EPA. There was a significant positive correlation between thein vitro production of prostacyclin and thein vivo production (as measured by the urinary prostacyclin metabolite level), despite the differences observed in the EPA-fed group. There was a high inter-animal variability in prostacyclin production using either method. These results indicate that dietary AA stimulates and dietary EPA reducesin vivo PGI₂ production in the rat. An equivalent amount of dietary LA was without effect.     

Effect of Euphorbia esula on Sheep Rumen Microbial Activity and Mass In Vitro

Most large herbivores avoid the invasive weed leafy spurge (Euphorbia esula L.), possibly because the plant contains secondary compounds including terpenoids and condensed tannins. On the other hand, E. esula has high nutritive value based on traditional measures such as crude protein, fiber, and dry matter disappearance and is consumed by sheep and goats. Our objective was to determine if material from undefoliated and previously defoliated E. esula shoots, mixed in different proportions with grass hay, adversely affects sheep rumen microbial activity and mass in vitro. Material from undefoliated and previously defoliated E. esula shoots was collected in June, July, and August 1994 near Grass Range, Montana. Usually, increasing levels of E. esula leaves and flowers in the mixtures increased in vitro dry matter and neutral detergent fiber disappearances (DMD, NDFD), microbial gas production, and microbial purine concentrations. In contrast, increasing levels of E. esula stems in the mixtures decreased DMD, NDFD, microbial gas production, and microbial purine concentrations. Rumen microbial gas production and purine concentrations were higher with leaves from previously defoliated than undefoliated shoots. In contrast, rumen microbial gas production and DMD were lowest for stems from previously defoliated shoots; these responses correlated with high concentrations of condensed tannins in stems of previously defoliated plants. In early summer, the high nutritive value of E. esula appears to offset any potential negative effects associated with secondary compounds. In late summer, microbial response appears more sensitive to the presence of secondary compounds, when nutritive value of this plant is declining.     

Adipogenic and Myogenic Potentials of Chicken Embryonic Fibroblasts in vitro: Combination of Fatty Acids and Insulin Induces Adipogenesis

The regulation of adipocyte differentiation is an important factor for production efficiency and meat quality in the poultry industry. The purpose of this study was to develop a new in vitro model of adipogenic differentiation of chicken embryonic fibroblasts (CEF). In this study, CEF were isolated at embryonic day (E) 5, and adipogenic differentiation was induced with supplementation of fatty acids (FA) and/or insulin (Ins) for 48 h. Oil-Red-O staining showed that lipid accumulation in E5 CEF was greater when supplemented with a combination of FA and Ins (FI) than other treatment groups (p < 0.05). Genes involved in differentiation of preadipocytes, fatty acid transport, and triacylglycerol synthesis were upregulated in the FI group compared to all other treatment groups (p < 0.01). Under myogenic media, the E5 CEF formed myotubes and expressed myogenic markers, myosin heavy chain (MHC), and myogenin (MyoG), suggesting myogenic potential of E5 CEF. To determine the permissive age window for adipogenic differentiation of CEF, E5, E6, and E7 CEF were induced for adipogenesis with FI treatment in 1%, 5%, or 10% chicken serum (CS). Among all embryonic ages, E5 with 10% CS showed the most lipid accumulation and the least myotube formation with the lowest expression of MHC and MyoG. These data indicate both adipogenic and myogenic potentials of E5 CEF, providing a new in vitro model for a better understanding of the processes of adipogenic and myogenic differentiation in chickens.     

Effect of vitamin E on pentane exhaled by rats treated with methyl ethyl ketone peroxide

One useful method to monitor in vivo lipid peroxidation is the measurement of volatile hydrocarbons, mainly pentane and ethane, that derive from unsaturated fatty acid hydroperoxides. Vitamin E, the biological antioxidant, inhibits lipid peroxidation and the production of pentane and ethane. The rates of pentane production by male Sprague-Dawley rats fed a diet that contained 10% vitamin E-stripped corn oil and 0, 1, 3, 5 or 10 IU dl-α-tocopherol acetate/kg were monitored over a 12-wk period. During the eleventh and twelfth weeks, the rats were injected intraperitoneally with 3.3 and 13 mg of methyl ethyl ketone peroxide (MEKP)/kg body wt, respectively. Pentane production was then measured at intervals over a 50-min period, and the total amount of pentane produced over this time interval was estimated. An asymptotic function was found to describe the relationship between exhaled pentane and the low levels of dietary vitamin E that were fed to the rats. As measured by pentane production, rats had a higher minimal vitamin E requirement after they were treated with the potent peroxidation initiator MEKP than they did prior to treatment. The level of pentane exhaled by rats injected with 13 mg MEKP/kg body wt was significantly correlated with kidney and spleen tocopherol levels.     

Studies in the development of antibacterial surfactants. II. performance of germicidal and deodorant soaps

Summary It has been shown that mixtures of hexachlorophene and trichlorocarbanilide or bithionol and trichlorocarbanilide in soap show a marked synergism with respect to antibacterial properties. In both cases the approximate ratio of 50/50 of the two components represents an optimum. Nonionic detergents enhance the antibacterial activity of trichlorocarbanilidein vitro when present at relatively low levels. At higher levels of nonionic the antibacterial agent is neutralized and loses its effectiveness. The antibacterial activity of the pair hexachlorophene-trichlorocarbanilide extends over a wide spectrum of micro-organisms, and synergism is shown with each test organism. High antibacterial activity of the synergistic pairs in soap is shown both inin vivo handwashing studies and in subjective deodorant tests. On the other hand, it is shown by way of several examples thatin vivo observations do not necessarily correlate within vitro bacteriological screening tests.     

Effectiveness of several polyunsaturated seed oils as boll weevil feeding deterrents

Prompted by the previous discovery that (9Z,11E,13E)-9,11,13-octadecatrienoic acid (α-eleostearic acid) was one of the compo-nents responsible for the boll weevil feeding deterrency of tung oil, the seeds of 11 other plant species were extracted with pentane and the oils were evaluated for their feeding deterrency in the laboratory. The oils ofCalendula suffruticosa, Centrantbus macro-siphon, Jacaranda mimosifolia andMomordica cochincbinenis were effective feeding deterrents for the boll weevil.     

Auswirkungen oxidierter Fettsäuren auf landwirtschaftliche Nutztiere bei Unterversorgung mit Vitamin E und Selen

Effects of Oxidized Fatty Acids on Agricultural Working Animals in Case of Insufficient Supply with Vitamin E and Selenium Diseases of agricultural working animals due to insufficient supply with vitamin E and selenium have been common knowledge for long. Especially in case of feeding with oxidized fats, rich in polyenic acid significant defects can occur. It could be detected in special tests with trouts (Salmo gairdnerii R.) that a low degree of oxidation (about POV 50) of the feed fat in case of sufficient supply with vitamin E and selenium is without any influence on growth and feed exploitation. Higher oxidized fats (about POV 250 and more) cause less increase in weight and above all defects on organs, which can be detected among others by certain parameters (haematocrit value, haemoglobine content, GOT, GPT, LDH, CK, Bilirubin). These effects can be avoided by higher doses of tocopherol. It exists, however, a dependency between the uptaken amount of fat and the period of additional feeding. A mixture of natural D-tocopherols in rations with high oxidized polyenic acids (POV 900–1700) was able to decrease or to avoid the noxious effect and losses of animals if the additional amount was increased. It turned out that there was an equivalency to D, L-α-tocopherol, even if there were great differences in the tocopherol equivalences.     

Effect of antioxidants on lipid peroxidation in iron-loaded rats

Indirect evidence has suggested that lipid peroxidation is associated with iron overload in vivo. As a measure of lipid peroxidation, pentane expired in the breath of rats loaded with an accumulated dose of either 100 mg or 186–200 mg of iron injected intraperitoneally as iron dextran was measured over a 7 to 8 week period, and the effect on pentane production of feeding antioxidant-supplemented diets was determined. By the seventh week of feeding the diets, rats fed 0.3% L-ascorbic acid produced 17% less (P=0.03) pentane than did rats fed the basal antioxidant-deficient diet, whereas rats fed 0.004% dl-α-tocopherol acetate produced 92% less (P<0.001). After being fed the basal diet for 7 weeks, iron-loaded rats produced 76±9 pmol pentane/100 g body wt/min. When synthetic antioxidants were added to the diet at a concentration of 0.25%, the order of effectiveness in decreasing pentane production after 1 week was: N,N′-diphenyl-p-phenylenediamine > ethoxyquin > butylated hydroxyanisole > butylated hydroxytoluene > propyl gallate ∼ no antioxidant. After removal of either ethoxyquin or N,N′-diphenyl-p-phenylenediamine from the diets for 1 week, pentane production increased to a high level. The total amount of lipid soluble fluorophores in individual spleens of rats fed N,N′-diphenyl-p-phenylenediamine, ethoxyquin, dl-α-tocopherol acetate, ascorbic acid and no antioxidant were correlated significantly with the corresponding total integrated amount of pentane produced by the individual rats over the 7 to 8 week period. This study has provided some of the most direct evidence to date that lipid peroxidation is associated with iron overload in vivo.     

Metabolism of long-chain fatty acids,alcohols and alkylglycerols in the fish parasiteParatenuisentis ambiguus (Acanthocephala)

Specific differences between the acyl composition of lipids on the helminthParatenuisentis ambiguus and its host eel, as shown previously, prompted us to study the lipid metabolism in this intestinal fish parasite. Adults and larvae ofP. ambiguus were fed various lipid precursors, e.g., fatty acids, long-chain alcohols and 1-O-alkylglycerols, which may occur as common nutrients of intestinal parasites. Incorporation of [1-¹⁴C]palmitic acid into neutral and polar lipids was found to be similar under aerobic and near-anaerobic conditions. In adult parasites maintained in culture medium supplemented with glucose, [1-¹⁴C]palmitic acid was incorporated mainly into triacylglycerols and phosphatidylcholines, whereas [1-¹⁴C]oleic acid was incorporated preferentially into triacylglycerols. In fasted adults, as well as in larvae, [1-¹⁴C]oleic acid was mainly transferred to phosphatidylcholines. Lipolytic activity was detected in adult parasites that had been incubated with radioactive trioleoylglycerol. [1-¹⁴C]Hexadecan-1-ol was oxidized inP. ambiguus at a high rate to labeled palmitic acid, which was incorporated into various lipid classes ofP. ambiguus. Small but significant proportions of radioactivity from hexadecan-1-ol were incorporated into ether glycerolipids of the parasite. A more direct precursor in ether glycerolipid metabolism, i.e.,rac-1-O-[1′-¹⁴C] hexadecylglycerol, was incorporated into alkyl and 1′-alkenyl moieties of choline and etha-nolamine etherglycerophospholipids ofP. ambiguus in high yield. High proportions of labeled diacylglycerols, triacylglycerols and steryl esters were detected in surface lipids as well as lipid extracts of the culture media after incubation ofP. ambiguus with [1-¹⁴C]palmitic or [1-¹⁴C]oleic acids. The results suggest that palmitic acid and oleic acid are incorporated into neutral and polar lipids ofP. ambiguus maintained in glucose medium quite differently with oleic acid showing a strong preference for triacylglycerols. However, the incorporation of palmitic acid in glucose-fed parasites was similar to that of oleic acid in fasted parasites, as well as in larvae. This may be explained by partial fatty acid depletion in fasted worms and rapid cell division in larvae, respectively.     

Calcium silicate hydrate—in-situ development of the silicate structure followed by infrared spectroscopy

In the current study, the development of the silicate structure of synthetic calcium silicate hydrates with different calcium contents was followed by in-situ infrared (IR) spectroscopy and correlated to the in-situ phase development evaluated by X-ray diffraction (XRD). A baseline correction method initially developed for X-ray diffractograms was successfully adapted for the complex background of the fingerprint region in in-situ IR, which significantly contributed to signal quality and reproducibility. The development of separate silicate infrared bands could be monitored over 24 h of reaction. These bands could be assigned to oligomeric and dimeric species based on their time and stoichiometry-dependent development. It was clearly shown that the main peak of the dimeric silicate species was overlooked in the literature. The correlation of time-dependent events to in-situ XRD revealed that changes in the unit cell of calcium silicate hydrate are related to silicate polymerization. The results were compared to ²⁹Si-MAS-NMR, which highlighted the benefits of in-situ IR spectroscopy.     

Effects of organic solvent extracts from herbage on feeding behavior in goats

The effects of organic solvent extracts from perennial ryegrass (Lolium perenne L. cv. Friend), orchardgrass (Dactylis glomerata L. cv. Akimidori) andLolium ×Festuca hybrid on the hay consumption of goats were measured by simple two-choice feeding assays. Orchardgrass hay treated with methanol extracts (resuspended in water) of perennial ryegrass showed an increased intake by goats compared to untreated hay (P < 0.01). The palatability of hay tended to be slightly decreased by spraying it with pentane extract of perennial ryegrass and orchardgrass. Furthermore, extracts of hybrid with pentane inhibited goats from feeding (P < 0.05). Methanol extract stimulated hay consumption whereas the pentane extracts did not change or reduce intake.     

Einfluß der Vitamin E-Supplementierung auf den antioxidativen Stoffwechsel des Ferkels bei unterschiedlicher Linolsäureversorgung

Influence of Vitamin E Supplementation on the Antioxidative Metabolism of Young Pigs at Different Intakes of Linoleic Acid To characterize the antioxidative metabolism of young pigs influenced by different vitamin E and linoleic acid concentrations in the diet, the in vitro pentane production of the liver microsomes, the α-tocopherol concentration in total liver and liver microsomes, and the fatty acid content of the liver microsomes were investigated. Increased vitamin E concentrations in the diet resulted in decreased pentane production, increased α-tocopherol concentration of total liver and microsomes and reduced absolute content of total fatty acids of the microsomes. However, the n-6-fatty acids decreased to a smaller degree than the saturated fatty acids. Increased supplementation with linoleic acid resulted in an elevated pentane production when the vitamin E concentration of the diet was low. The α-tocopherol concentration of total liver and microsomes were not influenced by increased supplementation of linoleic acid, however, the monoenoic fatty acid content of the microsomes was reduced.     

Sphingomyelin metabolism is linked to salt transport in the gills of euryhaline fish

Byin vivo andin vitro studies ofl-(3-³H)serine and [9,10(n)-³H]palmitic acid incorporation into phospholipids, we show a change in the renewal of the ceramide moiety of sphingomyelin in the gills of euryhaline fish (sea bass and eels) when the animals were subjected to abrupt alterations in environmental salinity.In vivo, decrease of the salinity from sea water (salinity 3.7%) to diluted sea water (salinity 1%) induced an increase of label incorporation into gill sphingomyelin. The same was true when gills from sea water-adapted sea bass or sea water-adapted eels were incubated in diluted sea water. A decrease in free ceramides synthesis was also observed in the gills of sea water-adapted sea bass when the salinity of the incubation medium was reduced. Direct inhibition of Na⁺/K⁺-ATPase activity with ouabain decreased the sphingomyelin synthesis in the gills of sea bass duringin vitro incubation in diluted sea water, whereas treatment with furosemide stimulated sphingomyelin synthesis in the same gills incubated in sea water. These findings indicate that changes in Na⁺ fluxes modify the sphingomyelin turnover and control the production of free ceramides and sphingosine in gill cells of euryhaline fish. In view of the well-known effects of these sphingomyelin degradation products on isolated tumor cell differentiation, we suggest that they play a very important role in modulating chloride cell distribution and metabolism of fish gills during abrupt changes in environmental salinity.     

Identification of triterpenoid feeding deterrent of red pumpkin beetles (Aulacophora foveicollis) fromMomordica charantia

The triterpenoids isolated from the leaves ofMomordica charantia Linn (bitter gourd) were found to elicit feeding-deterrent activity against red pumpkin beetles (Aulacophora foveicollis Lucas). The most abundant triterpenoid which deterred feeding was identified as momordicine II, 23-O--glucopyranoside of 3,7,23-trihydroxycucurbita-5,24-dien-19-al. A concentration of 3200g/ml and above of the triterpenoids caused significant reduction of feeding by red pumpkin beetles in in vitro bioassay experiments, which compared favorably with the levels of triterpenoids inM. charantia leaves found in nature.     

Beziehungen von Vitamin E zur Arteriosklerose

Relationship between Vitamin E and Arteriosclerosis Vitamin E deficiency in animals can lead to arteriosclerotic changes of blood vessels. Antioxidant vitamins A and E are, therefore, part of an important biological defense system. In this paper we describe effects of antioxidant vitamins on the synthesis of prostacyclin (PGI₂) by cultured human endothelial cells and on the mortality of middle-aged men due to ischemic heart diseases. In vitro studies on the induced prostacyclin (PGI₂) synthesis of cultured human endothelial cells from umbilical cord veins show an increased release of PGI₂ in the presence of vitamin E (all-rac-α-tocopherol) and trolox (rac-2-carboxy-6-hydroxy-2,5,7,8-tetramethylchroman). Cross-cultural epidemiological studies on different male populations (age 40 – 49 years, N = 12) throughout Europe show a statistically significant inverse correlation between the status of antioxidant vitamins A and E in plasma and the rate of mortality due to ischemic heart disease. In conclusion, the results of both the in vitro studies and the epidemiological surveys are consistent with the interpretation that antioxidant vitamins reduce damage induced by peroxidation of important biological structures, and hence limit the development of arteriosclerosis.     

Determination of lysine modification product ε-N-pyrrolylnorleucine in hydrolyzed proteins and trout muscle microsomes by micellar electrokinetic capillary chromatography

ε-N-Pyrrolylnorleucine (Pnl) is a product of the reaction between the lipid peroxidation product 4,5(E)-epoxy-2(E)-heptenal (EH) and the ε-amino group of lysine. Because Pnl might also be produced in proteins, a specific method to determine this compound in protein hydrolysates has been developed. Homoarginine, added as the internal standard, and Pnl are derivatized with diethyl ethoxymethylenemalonate and analyzed by micellar electrokinetic capillary chromatography. The method also analyzes lysine and arginine, and these analyses were useful in determining losses of these amino acids after treatment with EH. The lowest concentration of Pnl detected with acceptable reproductibility is 5 nmol/mL, and the coefficient of variation was determined from four standard curves assayed on separate days. Detector response was linear for samples containing 1.6 to 74 nmol/mL of Pnl. The assay was applied in investigations of Pnl production in bovine serum albumin (BSA) and trout muscle microsomes treated with EH. When BSA was incubated overnight with 30 mM EH, 76% of lysine residues were modified, and a part of these residues were detected as Pnl (12%). Pnl formation was also detected when trout muscle microsomes were incubated for three hours with 1 or 10 mM EH. These results show that Pnl is producedin vitro in proteins treated with the lipid peroxidation product EH, and suggest that Pnl might also be constituent ofin vivo damaged proteins by their reaction with oxidized lipids.     

Zur endogene Lipidperoxidation bei diätetischer Belastung des Masthuhns

Endogenous Lipid Peroxidation in Broiler Chickens under Dietary Loads Growing broiler chickens were fed a Vitamin E-deficient diet containing 10% reesterified triglyceride from soy-bean-oil. Six groups with day-old broiler chicken were supplemented with 0, 20 or 100 ppm of vitamin E. On each vitamin level one group was fed with the fresh fat, the other was supplied with the fat being oxidized. Clinical data and development of body weight were registered. The animals were euthanised after 3 weeks. Pentane production of liver mitochondria and microsomes was measured and tocopherol concentrations were determined as well as the GSH-PX-activity in liver cytosol and plasma. Deficiency of vitamin E together with a high level of dietary linoleic acid leads to an imbalance in peroxidative and antioxidative metabolism and finally to disease. It is discussed if the clinical signs after consumption of linoleic acid-rich oxidized oils are caused by specific toxic secundary products.     

Chemical Defense in <Emphasis Type="Italic">Elodea nuttallii</Emphasis> Reduces Feeding and Growth of Aquatic Herbivorous Lepidoptera

The submersed macrophyte Elodea nuttallii (Hydrocharitaceae) is invasive in Europe and frequently found in aquatic plant communities. Many invertebrate herbivores, such as larvae of the generalist aquatic moth, Acentria ephemerella (Lepidoptera, Pyralidae), avoid feeding on E. nuttallii and preferably consume native species. First instar larvae exhibited a high mortality on E. nuttallii compared to the native macrophyte Potamogeton perfoliatus. Mortality of older larvae was also high when fed E. nuttallii exposed to high light intensities. Growth of older larvae was strongly reduced on E. nuttallii compared to pondweeds (Potamogeton lucens). Neither differences in nitrogen nor phosphorus content explained the different performance on these submerged macrophytes, but plants differed in their flavonoid content. To investigate whether plant-derived allelochemicals from E. nuttallii affect larval performance in the same way as live plants, we developed a functional bioassay, in which Acentria larvae were reared on artificial diets. We offered larvae Potamogeton leaf disks coated with crude Elodea extracts and partially purified flavonoids. Elodea extracts deterred larvae from feeding on otherwise preferred Potamogeton leaves, and yet, unknown compounds in the extracts reduced growth and survival of Acentria. The flavonoid fraction containing luteolin-7-O-diglucuronide, apigenin-7-O-diglucuronide, and chrysoeriol-7-O-diglucuronide strongly reduced feeding of larvae, but did not increase mortality. The concentrations of these compounds in our assays were 0.01–0.09% of plant dry mass, which is in the lower range of concentrations found in the field (0.02–1.2%). Chemical defense in E. nuttallii thus plays an ecologically relevant role in this aquatic plant–herbivore system.