Incorporation of choline-1,2-14C into molecular species of phosphatidylcholine by alfalfa leaflet tissue

Alfalfa leaflet tissue incorporated choline-1,2-¹⁴C into at least 6 molecular speies of phosphatidylcholine. After 7 hr incubation the species containing palmitic and linoleic acids (16∶0–18∶2) and the species containing linolenic and linoleic acids (18∶3–18∶2) had the highest specific activities. After 24 hr incubation, the species containing palmitic and linolenic acids (16∶0–18∶3) and the species containing 2 linolenic acids (18∶3–18∶3) had the highest specific activities. The most likely interpretation of these data is that choline is accepted by diglycerides containing one linoleic acid residue and that this residue is then desaturated within the phosphatidylcholine molecule to linolenic acid. Contribution No. 39, C.D.A. Research Station, Ste-Foy, Quebec.     

Stability of low linolenic acid canola oil to frying temperatures

The effect of heating on the oxidation of low (1.6%) linolenic acid canola oil (C18∶3) at frying temperature (185 ±5°C) under nitrogen and air was examined and then compared to a laboratory deodorized (9.0%, C18∶3) and a commercially deodorized (8.5%, C18∶3) canola oil sample. A significantly lower development of oxidation was evident for the low C18:3 canola oil, based on the measurement of peroxide value (PV), thiobarbituric acid (TBA), free fatty acids (FFA), dienals and carbonyls. The greater stability of the low C18:3 canola oil was also reflected by a corresponding improvement in heated room odor intensity scores. Heating under nitrogen (rather than air) not only improved the odors but limited the oxidation in all oils. While the low C18:3 canola oil heated under nitrogen was acceptable in 94% of odor judgments the same oil heated in air was acceptable in only 44%. This suggests that even low levels of C18:3 may contribute to the development of the heated room odor phenomenon.     

Low-linolenic acid soybean oil—Alternatives to frying oils

Oil was hexane-extracted from soybeans that had been modified by hybridization breeding for low-linolenic acid (18∶3) content. Extracted crude oils were processed to finished edible oils by laboratory simulations of commercial oil processing procedures. Oils from three germplasm lines N83-375 (5.5% 18∶3), N89-2009 (2.9% 18∶3) and N85-2176 (1.9% 18∶3) were compared to commercial unhydrogenated soybean salad oil with 6.2% 18∶3 and two hydrogenated soybean frying oils, HSBOI (4.1% 18∶3) and HSBOII (<0.2% 18∶3). Low-18∶3 oils produced by hybridization showed significantly lower room odor intensity scores than the commercial soybean salad oil and the commercial frying oils. The N85-2176 oil with an 18∶3 content below 2.0% showed no fishy odor after 10 h at 190°C and lower burnt and acrid odors after 20 h of use when compared to the commercial oils. Flavor quality of potatoes fried with the N85-2176 oil at 190°C after 10 and 20 h was good, and significantly better at both time periods than that of potatoes fried in the unhydrogenated oil or in the hydrogenated oils. Flavor quality scores of potatoes fried in the N89-2009 oil (2.9% 18∶3) after 10 and 20 h was good and equal to that of potatoes fried in the HSBOI oil (4.1% 18∶3). Fishy flavors, perceived with potatoes fried in the low-18∶3 oils, were significantly lower than those reported for potatoes fried in the unhydrogenated control oil, and the potatoes lacked the hydrogenated flavors of potatoes fried in hydrogenated oils. These results indicate that oils with lowered linolenic acid content produced by hybridization breeding of soybeans are potential alternatives to hydrogenated frying oils.     

Effect of age and α-linolenic acid deficiency on Δ6 desaturase activity and liver lipids in rats

The combined effects of age and of diet deficient in n−3 fatty acids on Δ6 desaturation of linoleic acid and on lipid fatty acid composition were studied in the liver of the rat at 2, 6, 12, 18 and 24 mon of age. The profiles of Δ6 desaturase activity and fatty acid composition were studied in the deficient rats refed, at these different ages either with 18∶3n−3 (mixture of peanut and rapeseed oils) or with 20∶5n−3+22∶6n−3 (fish oil) diets for 2, 4, 8 or 12 wk. Results showed that the liver Δ6 desaturation activity in the control rats remained high at 2 and 6 mon, decreased by 30% from 6 to 12 mon, and then remained stable from 12 to 24 mon. In the deficient rats, this activity remained high during the entire period studied. Thus, the profile of liver Δ6 desaturase activity after puberty was not related to age only; it also depended on the polyunsaturated fatty acid (PUFA) n−6 and n−3 balance in the diet. In the controls, in parallel with the Δ6 desaturase activity, PUFA metabolism could be divided into three periods: a “young” period, and “old age” period, separated by a period of transition between 6 and 12 mon. Recovery from PUFA n−3 deficiency occurred at all ages but in a different manner depending on whether the rats were “young” or “old”. Recovery was faster if long-chain n−3 PUFA rather than α-linolenic acid were supplied in the diet.     

Linalyl oleate as a frying oil autoxidation inhibitor

Linalyl oleate (LO), an interesterification product of linalyl acetate (LA) and methyl oleate catalyzed with sodium methoxide, was studied to determine its effectiveness in retarding oxidative changes in soybean oil heated continuously at 180±5°C for 32 h. The identity of LO was established by GC-MS and NMR. LO was tested at levels of 0.05 and 0.1% and compared with the more commonly used synthetic autoxidation inhibitor methyl silicone (MS) at levels of 5 and 10 ppm. FA changes and conjugated dienoic acid formation were monitored. First-order kinetic equations were used to model the decreases in linoleate (18∶2)/palmitate and linolenate (18∶3)/palmitate ratios. Plots of the data show an inflection point at ∼11 h. Oils with either level of MS and LO had lower reaction rate constants before the inflection points, and lower conjugated diene values and higher 18∶2 and 18∶3 percentages at the end of the 32-h heating period than did oil without additives and with LA. LO could replace methyl silicone in soybean oil during deep-fat frying but at levels about 100 times greater. [We propose to use the term “autoxidation inhibitor” for substances that inhibit autoxidation when added to fats and oils at low concentrations and whose mechanism of action may be unknown. Some may wish to call such substances “antioxidants” but others wish to reserve this term for substances that end free radical chains by hydrogen radical donation. Some refer to methyl silicone as a “polymerization inhibitor”, but this term suggests more about its mechanism of action than seems warranted.]     

Effects of different dietary intake of essential fatty acids on C20∶3ω6 and C20∶4ω6 serum levels in human adults

Four diets which differed in fatty acid composition were provided for five months each to a group of 24 healthy nun volunteers. The diets contained 54% carbohydrates, 16% proteins and 30% lipids. One-third of the lipid part remained unchanged during the whole study, and two-thirds were modified during each period. For this latter portion, one of the following dietary fats was used: sunflower oil, peanut oil, low erucic acid rapeseed (LEAR) oil or milk fats. This procedure allowed an evaluation of the effects of various amounts of dietary linoleic acid (C18∶2ω6) and alpha-linolenic acid (C18∶3ω3) on the serum level of their metabolites. A diet providing a large amount of linoleic acid (14% of the total caloric intake) resulted in low levels of dihomo-gamma-linolenic acid (C20∶3ω6) and arachidonic acid (C20∶4ω6) in serum phospholipids and cholesteryl esters. A diet providing a small amount of linoleic acid (0.6% to 1.3% of the total caloric intake) induced high levels of ω6 fatty acid derivatives. Intermediate serum levels of C20∶3ω6 and C20∶4ω6 were found with a linoleic acid supply of about 6.5% of the total caloric intake. Serum levels of ω6 metabolites were not different after two diets providing a similar supply of C18∶2ω6 (4.5% to 6.5% of the total caloric intake), although in one of them the supply of C18∶3ω3 was higher (1.5% for LEAR oil versus 0.13% for peanut oil). Under our experimental conditions (healthy human adults fed on a normo-caloric diet with 30% lipids), we tried to determine PUFA (linoleic and linolenic acid) allowances which should be recommended for adults. The aim of the study was to obtain a hypocholesterolemic or normocholesterolemic effect while keeping normal 20∶3ω6 and 20∶4ω6 serum levels which would evidence a normal linoleic acid metabolism. The amounts recommended are: linoleic acid 5 to 6% of the total calories; alpha-linolenic acid 0.5 to 1% of the total calories.     

Toward increasing erucic acid content in oilseed rape (<Emphasis Type="Italic">Brassica napus</Emphasis> L.) through the combination with genes for high oleic acid

Erucic acid (22∶1) is a valuable renewable resource that has several applications in the oleochemical industry. High 22∶1 rapeseed (HEAR) contains around 50% 22∶1. For its technical use it is desirable to increase the 22∶1 content and to decrease the eicosenoic acid (20∶1), PUFA (18∶2+18∶3), and saturated FA (16∶0+18∶0) contents. In the present experiment, HEAR was crossed to high oleic acid rapeseed (ca. 85% 18∶1) with the hypothesis that a combination of the involved genes should lead to a reduced 18∶1 desaturation and to an increased availability of oleoyl-CoA, which should result in enhanced 22∶1 synthesis. A NIR spectroscopic calibration for 22∶1 was developed for single seeds, and the calibration was used to select, in a nondestructive manner, F₂ seeds high in 22∶1. Selected F₂ seeds were sown in the field and F₃ seeds were harvested. The results of the FA analysis showed recombinant genotypes with increased total monounsaturated FA (22∶1+20∶1+18∶1) of up to 89% and decreased PUFA (<8%) and saturated FA content (<3.5%). There was no significant difference in 22∶1 content, but a 3 to 5% increase in 20∶1 content was observed in comparison to the HEAR parental cv. Maplus. Results were confirmed following cultivation of selected plant material a second year in the field. The present study revealed that there are other biochemical limitations than the pool of available oleoyl-CoA that restrict FA elongation to 22∶1 in rapeseed. The generated high 22∶1 plant material with an increased 18∶1 content may be useful in further studies to identify these limitations.     

Influence of dietary fat composition on intestinal absorption in the rat

Omega-3 fatty acids influence the function of the intestinal brush border membrane. For example, the omega-3 fatty acid eicosapentaenoic acid (20∶5ω3) has an antiabsorptive effect on jejunal uptake of glucose. This study was undertaken to determine whether the effect of feeding α-linolenic acid (18∶3ω3) or EPA plus docosahexaenoic acid (22∶6ω3) on intestinal absorption of nutrients was influenced by the major source of dietary lipid, hydrogenated beef tallow or safflower oil. Thein vitro intestinal uptake of glucose, fatty acids and cholesterol was examined in rats fed isocaloric diets for 2 weeks: beef tallow, beef tallow + linolenic acid, beef tallow + eicosapentaenoic acid/docosahexaenoic acid, safflower oil, safflower oil + linolenic acid, or safflower oil + eicosapentaenic acid/docosahexaenoic acid. Eicosapentaenoic acid/docosahexaenoic acid reduced jejunal uptake of 10 and 20 mM glucose only when fed with beef tallow, and not when fed with safflower oil. Linolenic acid had no effect on glucose uptake, regardless of whether it was fed with beef tallow or safflower oil. The jejunal uptake a long-chain fatty acids (18∶0, 18∶2ω6, 18∶3ω3, 20∶4ω6, 20∶5ω3 and 22∶6ω3) and cholesterol was lower in salfflower oil than with beef tallow. When eicosapentaenoic acid/docosahexaenoic acid was given with beef tallow (but not with safflower oil), there was lower uptake of 18∶0, 20∶5ω3 and cholesterol. The demonstration of the inhibitory effect of linolenic acid or eicosapentaenoic acid/docosahexaenoic acid on cholesterol uptake required the feeding of a saturated fatty acid diet (beef tallow). These changes in uptake were not explained by differences in the animals’ food intake, body weight gain or intestinal weight. Feeding safflower oil was associated with an approximately 25% increase in the jejunal and ileal mucosal surface area, but this increase was prevented by combining linolenic acid or eicosapentaenoic acid/docosahexaenoic acid with safflower oil. Different inhibitory patterns were observed when mixtures of fatty acids were present together in the incubation medium, rather than in the diet: for example, when 18∶0 was in the incubation medium with 20∶4ω6, the uptake of 20∶4ω6 was reduced, whereas the uptake was unaffected by 18∶2ω6 or 20∶5ω3. Thus, (1) the inhibitory effect of eicosapentaenoic acid/docosahexaenoic acid on jejunal uptake of glucose, fatty acids and cholesterol was influenced by the major dietary lipid, saturated (beef tallow) or polyunsaturated fatty acid (safflower oil); and (2) different omega-3 fatty acids (linolenic acid versus eicosapentaenoic acid/docosahexaenoic acid) have a variable influence on the intestinal absorption of nutrients.     

Varietal difference in lipid content and fatty acid composition of highbush blueberries

Lipids from five cultivars of highbush blueberries (Vaccinium corymbosum L.) were extracted and fractionated into neutral lipids (60–66%), glycolipids (20–22%) and phospholipids (14–18%). The major fatty acids in all fractions were palmitic (16∶0), oleic (18∶1), linoleic (18∶2), and linolenic (18∶3) acids. All lipid classes had a large concentration of C₁₈ polyunsaturated acids (84–92%), indicating that blueberries are a rich source of linoleic and linolenic acids. Changes in the fatty acid composition of neutral lipids and phospholipids were not significantly different among the five cultivars, but significant differences were noted in the ratios of linoleic and linolenic acids in the glycolipids fraction.     

Seed oil fatty acids of loasaceae—A new source of γ-linolenic and stearidonic acids

The pharmaceutically interesting Δ6-FA 18∶3Δ6c, 9c, 12c (γ-linolenic acid) and 18∶4Δ6c,9c,12c,15c (stearidonic acid) appear to have evolved independently several times during plant phylogenetic evolution. They typically occur in “clusters” of a few closely related species or genera in about a dozen different plant families throughout the plant kingdom. A hither-unknown “cluster of occurrence” has now been discovered in the New World plant family Loasaceae. γ-Linolenic and stearidonic acids occur exclusively in representatives of the newly described genus Nasa at significance levels of between 3 and 10% each. Nasa had recently been separated from the older, more broadly circumscribed genus Loasa. The two Δ6-FA were not found in the closely related genus Loasa sensu stricto, nor in a number of other representatives of Loasaceae.     

Desaturation and chain elongation of essential fatty acids in isolated liver cells from rat and rainbow trout

Isolated hepatocytes from rainbow trout and rat were incubated with¹⁴C-labeled linoleic acid, linolenic acid, dihomogammalinolenic acid or eicosapentaenoic acid. The most striking difference in the desaturase activity was the lower level of Δ5 desaturase in trout than in rat. No Δ4 desaturation of 22∶4(n−6) to 22∶5(n−6) was observed in either of the two species, while the conversion of 22∶5(n−3) to 22∶6(n−3) was significant in both groups and highest in rainbow trout. The chain-elongating activity was remarkably similar in the two species, except for the “dead-end” elongation which was distinctly more important in fish.     

Polyenoic acid metabolism in cultured human skin fibroblasts

The incorporation of [1-¹⁴C]linoleic acid, and [1-¹⁴C]linoleic acid into cellular lipids of cultured human skin fibroblasts was studied. Cultured cells took up both labeled fatty acids at nearly the same rate and incorporated them into a variety of lipid classes. At the end of 1 hr incubation with [1-¹⁴C]linoleic acid, radioactivity was found in the triacylglycerol (TG) and choline phosphoglyceride (CPG) pools preferentially. Incorporation into the TG fraction decreased rapidly, while the uptake into CPG, serine phosphoglyceride (SPG), and ethanolamine phosphoglyceride (EPG) fractions increased progressively with longer incubation times. Similar results were obtained with [1-¹⁴C]linoleic acid as precursor. At the end of 24 hr, desaturation and chain elongation of 18∶3 n−3 was more extensive than conversion of 18∶2 n−6 to higher polyenoic acids. During pulse-chase experiments with either fatty acid precursor, the incorporated radioactivity was progressively lost from cellular lipids, particularly from the TG and CPG fractions, but continued to increase in the SPG and EPG pools. The similar labeling pattern of cellular phospholipids with linoleic or linolenic acids, and data from pulse-chase studies suggest that a direct transfer of fatty acids from CPG to EPG is a likely pathway in fibroblast cultures. Incorporation into the EPG pool during the pulse-chase experiments paralleled extensive desaturation and elongation of linoleic acid into 20∶4 n−6, and 22∶4 n−6; and of linolenic acid into 22∶5 n−3 and 22∶6 n−3.     

Norflurazon—An inhibitor of essential fatty acid desaturation in isolated liver cells

Norflurazon is a herbicide known to inhibit carotene biosynthesis and linolenic acid biosynthesis in plants. In the present work, the effect of norflurazon on the metabolism of essential fatty acids was studied in isolated rat liver cells and in rat liver microsomes, incubated with [1-¹⁴C] labeled linolenic acid (18∶3, n−3), dihomogammalinolenic acid (20∶3, n−6) and eicosapentaenoic acid (20∶5, n−3). Norflurazon (0.1 mM, 1.0 mM) was found to inhibit essential fatty acid desaturation. The Δ6 desaturation is inhibited more efficiently than the Δ5 and Δ4 desaturation. The chain elongation of essential C₁₈ fatty acids to their C₂₀ and C₂₂ homoglogs was not inhibited by norflurazon.     

Effects of dietary supplementation of rapeseed oil on metabolism of [1-<Superscript>14</Superscript>C]18∶1n−9, [1-<Superscript>14</Superscript>C]20∶3n−6, and [1-<Superscript>14</Superscript>C]20∶4n−3 in atlantic salmon heaptocytes

Atlantic salmon were fed fish meal-based diets supplemented with either 100% fish oil (FO) or 100% rapeseed oil (RO) from an initial weight of 85 g to a final average weight of 280 g. The effects of these diets on the capacity of Atlantic salmon hepatocytes to elogate, desaturate, and esterify [1-¹⁴C]18∶1n−9 and the immediate substrates for the Δ⁵ desaturase, [1-¹⁴C]20∶3 n−6 and [1-¹⁴C]20∶4n−3, were investigated. Radiolabeled 18∶1n−9 was mainly esterified into cellular TAG, whereas the more polyunsaturated FA, [1-¹⁴C]20∶3n−6 and [1-¹⁴C]20∶4n−3, were primarily esterified into cellular PL. More of the elongation product, [1-¹⁴C]20∶1n−9, was produced from 18∶1n−9 and more of the desaturation and elongation products, 22∶5n−6 and 22∶6n−3, were produced from [1-¹⁴C]20∶3n−6 and [1-¹⁴C]20∶4n−3, respectively, in RO hepatocytes than in FO hepatocytes. Further, we studied whether increased addition of [1-¹⁴C]18∶1n−9 to the hepatocyte culture media would affect the capacity of hepatocytes to oxidize 18∶1n−9 to acid-soluble products and CO₂. An increase in exogenous concentration of 18∶1n−9 from 7 to 100 μM resulted in a nearly twofold increase in the amount of 18∶1n−9 that was oxidized. The conversion of 20∶4n−3 and 20∶3n−6 to the longer-chain 22∶6n−3 and 22∶5n−6 was enhanced by RO feeding in Atlantic salmon hepatocytes. The increased capacity of RO hepatocytes to produce 22∶6n−3 was, however, not enought to achieve the levels found in FO hepatocytes. Our data further showed that there were no differences in the hepatocyte FA oxidation capacity and the lipid deposition of carcass and liver between the two groups.     

Molecular markers associated with linolenic acid content in soybean

An altered FA profile with decreased linolenic (18∶3) acid in soybean germplasm was developed by crossing N97-3708-13, a soybean line with reduced 18∶3 (<5.4%) and ‘Anand’, a normal soybean cultivar (9.7% 18∶3). The resulting recombinant inbred lines are promising because they may promote healthier oil with improved oxidative stability and flavor. The objective of this study was to utilize the population N97-3708-13 × Anand to identify simple sequence repeat (SSR) markers associated with 18∶3 content. Two markers, Satt534 and Satt560, which are located approximately 10 cM apart from each other, near the Fan locus on linkage group B2, were identified as quantitative trait loci significantly associated with 18∶3 content (P=0.001, R ²=0.59, individually). The SSR markers identified in this study should be useful for implementation of marker-assisted selection for low-18∶3 genotypes in soybean breeding programs.     

Opportunities and problems in modification of levels of rapeseed C18 unsaturated fatty acids

Selections for different levels of C₁₈ fatty acids in rapeseed to date have had only limited success, due in part to the low frequency of occurrence of desired genotypes with increased linoleic and decreased linolenic acid. In the progeny of mutation experiments with seeds of the variety Oro (linolenic acid content 8–10%) two stable mutants were selected, one with 5% and the other with 20% linolenic acid in the seed oil. The level of linoleic acid in the two mutants is the same as Oro (16–20%), but the levels of oleic and linolenic acids are inversely altered. In this paper several problems associated with selecting for linoleic and linolenic acids, which became apparent during the mutation studies, are discussed. Many selections made from the mutated material were unstable, reverting to the original Oro fatty acid composition after two or three self-pollinated generations. This fact plus environmental and maternal effects made selection difficult. However, with the use of rapid and simple analytical methods and space-saving growing techniques, these difficulties were overcome. One of six papers presented in the symposium “Rapeseed Marketing and Breeding,” AOCS Meeting, Ottawa, September 1972.     

Geometrical isomerization of linolenic acid during heat treatment of vegetable oils

Heat treatment of rapeseed (primor) and soybean oils resulted in the geometrical isomerization of linolenic acid. The geometrical isomers were isolated from a rapeseed oil heated at 240 C for 10 hr by a combination of thin layer chromatography (TLC) of the methoxy bromomercuric adducts of the total methyl esters and AgNO₃-TLC. Three major isomers were identified after hydrazine reduction followed by ozonolysis in BF₃-MeOH as 18:3Δ9c, 12c, 15t, 18:3Δ9t, 12c, 15c and 18:3Δ9t, 12c, 15t. These were accompanied by minor amounts of 18:3Δ9c, 12t, 15c, 18:3Δ9c, 12t, 15t and 18:3Δ9t, 12t, 15c. The 18:3 isomers were detected in both soybean and rapeseed oil heated at 240 C for 10 hr. At this temperature, the increase in time of the heat treatment from 10 to 40 hr resulted in a relative increase of the di-trans and in a decrease of the mono-trans isomers. Only minor quantities of these isomers were detected in the oils heated at 200 C for 10 hr. At this temperature, the increase in time of the heat treatment resulted in an increase of both the mono- and di-trans isomers. Presented in part at the I.S.F. Congress, October 1983, Budapest, Hungary.     

Lipid metabolism of the yellow clam,Mesodesma mactroides: 2-Polyunsaturated fatty acid metabolism

The fate of labeled linoleic, α-linolenic, and higher homologs of α-linolenic acid administered to the yellow clam,Mesodesma mactroides, was investigated. It was found that the clam incorporated the acids dissolved in sea water and converted 18∶2 (n−6) into 20∶2 (n−6) and 18∶3 (n−3) into 18∶4 (n−3) and 20∶3 (n−3). The addition of casein hydrolysate to the sea water increased the desaturation capacity of the clam and allowed the conversion of 18∶2 (n−6) into 18∶3 (n−6) to be demonstrated. An enhanced desaturation of 18∶3 (n−3) into 18∶4 (n−3) was also demonstrated. After 12 hr administration of the acid, no radioactivity was found in arachidonic, 20∶5 (n−3), or 22∶6 (n−3). Feeding the clams a culture ofPhaeodactylum tricornutum previously incubated with 1-¹⁴C-α-linolenic acid demonstrated that all the homologs of the α-linolenic series were found in the clam without any important changes. Six hour administration of labeled linolenic acid resulted in the incorporation of the acid into diglycerides and phospholipids. Member of the carrera del Investigador Cientifico of the Consejo Nacional de Investigaciones Cientificas y Tecnicas     

Fatty acid composition of lipids fromSaccharomyces fragilis

Lipids extracted fromSaccharomyces fragilis, grown in whey and deproteinized whey, were similar in amount and fatty acid composition. On a dry weight basis, the yeasts contained 3.0% total lipid and 0.5% saponifiable lipid. The fatty acids identified by gas chromatography-mass spectrometry were 2.5% C14∶0, 19.2% C16∶0, 11.9% C16∶1, 1.28% C16∶2, 3.4% C18∶0, 27.0% C18∶1, 25.1% C18∶2, and 9.6% C18∶3 with less than 1% of the following fatty acids present: C10∶0, C12∶0, C14∶1, C15∶0, and C17∶0.     

Dietary fats containing concentrates ofcis ortrans octadecenoates and the patterns of polyunsaturated fatty acids of liver phosphatidylcholine and phosphatidylethanolamine

The effects of the mixedcis- 18∶1 isomers and mixedtrans-18∶1 isomers present in partially hydrogenated soybean oil (PHSO) upon the patterns of polyunsaturated fatty acids (PUFA) in liver phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were studied in rats fed concentrates ofcis- 18∶1 ortrans- 18∶1 isomers isolated as triacylglycerides from PHSO. Thecis- 18∶1 andtrans- 18∶1 concentrates were fed at levels equal to those present in PHSO fed at 17.9% of the diet. All diets contained the required amounts of both linoleic and linolenic acids. Thetrans- 18∶1 concentrate was found to suppress the levels of 20∶4ω6 and 20∶3ω9, and to increase the levels of 18∶2ω6 and 20∶5ω3 in PC and PE. Thecis- 18∶1 concentrate suppressed 20∶4ω6 in PC, 20∶5ω3 in PC and PE, and 18∶2ω6 was more effective than thetrans concentrate in suppressing 22∶6ω3. Thetrans- 18∶1 concentrate was more effective in suppressing 20∶4ω6. Thetrans-18∶ isomers appear to modify PUFA metabolism by inhibition of PUFA synthesis, whereas thecis- 18∶1isomers appear to compete with 2-position fatty acyl transfer and to inhibit ω3 PUFA acylation.