Effect of dietary α-linolenic acid and its ratio to linoleic acid on platelet and plasma fatty acids and thrombogenesis

The effect of dietary α-linolenic acid (18∶3n−3) and its ratio to linoleic acid (18∶2n−6) on platelet and plasma phospholipid (PL) fatty acid patterns and prostanoid production were studied in normolipidemic men. The study consisted of two 42-d phases. Each was divided into a 6-d pre-experimental period, during which a mixed fat diet was fed, and two 18-d experimental periods, during which a mixture of sunflower and olive oil [low 18∶3n−3 content, high 18∶2/18∶3 ratio (LO-HI diet)], soybean oil (intermediate 18∶3n−3 content, intermediate 18∶2/18∶3 ratio), canola oil (intermediate 18∶3n−3 content, low 18∶2/18∶3 ratio) and a mixture of sunflower, olive and flax oil [high 18∶3n−3 content, low 18∶2/18∶3 ratio (HI-LO diet)] provided 77% of the fat (26% of the energy) in the diet. The 18∶3n−3 content and the 18∶2/18∶3 ratio of the experimental diets were: 0.8%, 27.4; 6.5%, 6.9; 6.6%, 3.0; and 13.4%, 2.7, respectively. There were appreciable differences in the fatty acid composition of platelet and plasma PLs. Nevertheless, 18∶1n−9, 18∶2n−6 and 18∶3n−3 levels in PL reflected the fatty acid composition of the diets, although very little 18∶3n−3 was incorporated into PL. Both the level of 18∶3n−3 in the diet and the 18∶2/18∶3 ratio were important in influencing the levels of longer chain n−3 fatty acid, especially 20∶5n−3, in platelet and plasma PL. Production of 6-keto-PGF_1α was significantly (P<0.05) higher following the HI-LO diet than the LO-HI diet although dietary fat source had no effect on bleeding time or thromboxane B₂ production. The present study showed that both the level of 18∶3n−3 in the diet and its ratio to 18∶2n−6 were important in influencing long-chain n−3 fatty acid levels in platelet and plasma PL and that prostanoid production coincided with the diet-induced differences in PL fatty acid patterns.     

Omega-3 fatty acid and cholesterol content of newly hatched chicks from α-linolenic acid enriched eggs

Egg yolk was enriched with α-linolenic acid (18∶3n−3) by feeding laying hens diets containing flax, canola or soybean seeds. Fertilized eggs were incubated and the fatty acid composition of whole body, liver, plasma, brain and the cholesterol content of plasma and liver tissue of the hatched chicks were studied. Eggs enriched with 18∶2n−6 fatty acids by feeding hens diets containing sunflower seeds were used as the controls. Feeding flax enriched (P<0.05) egg yolk and the developing progeny with 18∶3n−3, 20∶5n−3, 22∶5n−3 and 22∶6n−3. Feeding sunflower seeds resulted in an increase (P<0.05) of 18∶2n−6, 20∶4n−6, 22∶4n−6 and 22∶5n−6. The predominant polyunsaturated fatty acid of the brain was docosahexaenoic acid (22∶6n−3) which was higher (P<0.05) in the flax and canola fed group. The cholesterol content of the liver tissue was lower (P<0.05) in chicks hatched from hens fed flax seeds. This study indicates that 18∶3n−3 and 18∶2n−6 in the maternal diet are potent modulators of long-chain polyunsaturated n−3 or n−6 fatty acid and of cholesterol content in the developing progeny.     

Slow recovery of the fatty acid composition of sciatic nerve in rats fed a diet initially low in n−3 fatty acids

The sciatic nerve of rats fed sunflower oil (6 mg 18∶3n−3/100 g of diet) presented dramatic alterations in the long chain polyunsaturated fatty acids in comparison with those fed soy oil (130 mg 18∶3n−3/100 g of diet). In both 15-day-old and 60-day-old animals fed sunflower oil, 22∶6n−3 (cervonic acid) was fourfold less, 22∶5n−6 was 10-fold greater; adrenic acid (22∶4n−6) was slightly greater and arachidonic acid (20∶4n−6) was close to that in rats fed soy oil. The percentage distribution of total polyunsaturated fatty acids as well as the individual saturated and monounsaturated fatty acids were the same in both groups. When the sunflower oil-fed animals were switched to a soy oil-containing diet for either 15 or 60 days, the percentage distribution of 22∶6n−3 increased slowly to reach the control value 2.5 months later. Conversely 22∶5n−6 decreased slowly. The decay of 22∶5n−6 was more rapid than the increase of 22∶6n−3.     

Fatty acyl desaturation in isolated hepatocytes from Atlantic salmon (Salmo salar): Stimulation by dietary borage oil containing γ-linolenic acid

The effects of different dietary oils on the fatty acid compositions of liver phospholipids and the desaturation and elongation of [1-¹⁴C]18∶3n−3 and [1-¹⁴C]18∶2n−6 were investigated in isolated hepatocytes from Atlantic salmon. Atlantic salmon smolts were fed diets containing either a standard fish oil (FO) as a control diet, a 1∶1 blend of Southern Hemisphere marine oil and tuna orbital oil (MO/TO), sunflower oil (SO), borage oil (BO), or oliver oil (OO) for 12 wk. The SO and BO diets significantly increased the percentages of 18:2n−6, 18:3n−6, 20:2n−6, 20:3n−6, and total n-6 polyunsaturated fatty acids (PUFA) in salmon liver lipids in comparison with the FO diet. The BO diet also increased the percentage of 20:4n−6. Both the SO and BO diets significantly reduced the percentages of all n−3 PUFA in comparison with the FO diet. The OO diet significantly increased the percentages of 18:1n−9, 18:2n−6, total monoenes, and total n−6 PUFA in liver lipids compared to the FO diet, and the percentages of all n−3 PUFA were significantly reduced. With [1-¹⁴C]18:3n−3, the recovery of radioactivity in the products of Δ6 desaturation was significantly greater in the hepatocytes from salmon fed SO, BO, and OO in comparison with the FO diet. The BO diet also increased the recovery of radioactivity in the products of Δ5 desaturation. Only the BO diet significantly affected the desaturation of [1-¹⁴C]18:2n−6, increasing recovery of radioactivity in both Δ6- and Δ5-desaturation products. In conclusion, dietary BO, enriched in γ-linolenic acid (18:3n−6), significantly increased the proportions of both 20:3n−6 and 20:4n−6 in salmon liver phospholipids and also significantly increased the desaturation of both 18:2n−6 and 18:3n−3 in salmon hepatocytes. The possible relationships between dietary fatty acid composition, tissue phospholipid fatty acid composition, and desaturation/elongation activities are discussed.     

Incorporation ofcis- andtrans-octadecenoic acids into the membranes of rat liver mitochondria

The incorporation of dietary isomeric fatty acids into the membranes of liver mitochondria was investigated. Three groups of rats were fed diets containing 3% sunflower seed oil plus 15%, 20%, or 25% partially hydrogenated arachis oil. A fourth group was fed 25% partially hydrogenated arachis oil, but no sunflower seed oil. All diets were given for 3, 6, or 10 weeks. After 10 weeks, the content oftrans fatty acids in the lipids of the mitochondrial membranes was 15–19% of the total fatty acids. The composition of thetrans- and thecis-octadecenoic acids in the lipids of the mitochondrial membranes was similar for all groups supplemented with sunflower seed oil (SO), irrespective of time and dietary level of partially hydrogenated arachis oil (HAO). Thecis 18∶1 (n−8), which was a major isomer of the partially hydrogenated arachis oil, was almost excluded from the mitochondrial fatty acids. Likewise, the content oftrans 18∶1 (n−8) was considerably lower in the mitochondrial lipids than in the diet. On the contrary, the content oftrans 18∶1 (n−6) was higher in the mitochondrial lipids than in the diet. In the group fed without sunflower seed oil, isomers of linoleic acid and arachidonic acid were observed in the lipids of mitochondrial membranes. Presented in part at the ISF Congress, Marseille, September 1976.     

Major clofibrate effects on liver and plasma lipids are independent of changes in polyunsaturated fatty acid composition induced by dietary fat

The effects of clofibrate on the content and composition of liver and plasma lipids were studied in mice fed for 4 wk on diets enriched in n−6 or n−3 polyunsaturated fatty acids (PUFA) from sunflower oil (SO) or fish oil (FO), respectively; both oils were fed at 9% of the diet (dry weight basis). Only FO was hypolipidemic. Both oil regimes led to slightly increased concentrations of phospholipids (PL) and triacylglycerols (TG) in liver as compared with a standard chow diet containing 2% fat. Clofibrate promoted hypolipidemia only in animals fed SO. Its main effect was to enlarge the liver, such growth increasing the amounts of major glycerophospholipids while depleting the TG. SO and FO consumption changed the proportion of n−6 or n−3 PUFA in liver and plasma lipids in opposite ways. After clofibrate action, the PUFA of liver PL were preserved better than in the absence of oil supplementation. However, most of the drug-induced changes (e.g., increased 18∶1n−9 and 20∶3n−6, decreased 22∶6/20∶5 ratios) occurred inrrespective of lipids being rich in n−6 or n−3 PUFA. The concentration of sphingomyelin (SM), a minor liver lipid that virtually lacks PUFA, increased with the dietary oils, decreased with clofibrate, and changed its fatty acid composition in both situations. Thus. oil-increased SM had more 22∶0 and 24∶0 than clofibrate-decreased SM, which was significantly richer in 22∶1 and 24∶1.     

Effect of diets rich in linoleic or α-linolenic acid on phospholipid fatty acid composition and eicosanoid production in atlantic salmon (Salmo salar)

Atlantic salmon post-smolts were fed diets rich in linoleic acid (sunflower oil, SO), α-linolenic acid (linseed oil, LO) or long-chain polyunsaturated fatty acids (fish oil, FO) for a period of 12 wk. In the liver phospholipids of fish fed SO, the levels of 18∶2n−6, 20∶2n−6, 20∶3n−6 and 20∶4n−6 were significantly elevated compared to both other treatment. In choline phospholipids (CPL), ethanolamine phospholipids (EPL) and phosphatidylserine (PS) the levels of 22∶4n−6 and 22∶5n−6 were significantly elevated in fish fed SO. In liver phospholipids from fish fed LO, 18∶2n−6, 20∶2n−6 and 20∶3n−6 were significantly elevated but 20∶4n−6, 22∶4n−6 and 22∶5n−6 were similar or significantly decreased compared to fish fed FO. Liver phospholipids from fish fed LO had increased 18∶3n−3 and 20∶4n−3 compared to both other treatments while EPL and phosphatidylinositol (PI) also had increased 20∶5n−3. In fish fed LO, 22∶6n−3 was significantly reduced in CPL, PS and PI compared to fish fed FO. Broadly similar changes occurred in gill phospholipids. Production of 12-lipoxygenase metabolites in isolated gill cells stimulated with the Ca²⁺-ionophore A23187 were significantly reduced in fish fed either SO or LO compared to those fed FO. However, the ratio 12-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE)/12-hydroxy-5,8,10,14,17-eicosapentaenoic acid (12-HEPE) was significantly elevated in stimulated gill cells from SO-fed fish. Although mean values of thromboxane B₂ (TXB₂) and prostaglandin E₂ (PGE₂) were increased in fish fed SO, they were not significantly different from those of the other two treatments.     

Interactive effects of prenatal ethanol and N−3 fatty acid supplementation on brain development in mice

This study assesses the combined effects on brain and behavioral development of ethanol administration and supplementation of the maternal diet with long chain n−3 polyunsaturated fatty acids. From day 7 to 17 of gestation, pregnant mice were fed equivalent daily amounts of isocaloric liquid diets; 20% of the energy was provided by either ethanol or maltose-dextrin, and a further 20% by either safflower oil (rich in linoleic acid, 18∶2n−6), or a combination of safflower oil with a fish oil concentrate (rich in eicosapentaenoic acid, 20∶5n−3, and docosahexaenoic acid, 22∶6n−3). On day 18 the liquid diets were replaced by lab chow; a fifth group was maintained on lab chow throughout the experiment. Measures on the pups included brain weight and the fatty acid composition of the brain phospholipids on days 22 and 32 post-conception (birth=day 19), as well as behavioral development. Maternal weight gain during gestation was decreased by ethanol relative to maltose-dextrin, and increased by fish relative to safflower oil. On day 32, the brain weight of ethanoltreated animals fed fish oil was greater than their safflower oil controls, whereas the reverse was true in the two maltose-dextrin groups; a similar trend was apparent on day 22. The brain phospholipid content of the longer chain fatty acids (20∶4n−6, 22∶4n−6, 22∶5n−6, 20∶5n−3, 22∶5n−3, 22∶6n−3) on day 22 reflected that of the prenatal diet, with the proportion of n−3 compounds being higher and that of n−6 floer in the fish oil than safflower oil groups. Prenatal dietary effects were absent by day 32, with the exception of lower 22∶5n−6 in fish oil groups. Dietary supplementation with n−3 fatty acids increased the ratio of 20∶3n−6 to 20∶4n−6, which is consistent with a blockade of the activity of Δ-5 desaturase. On day 22 the incorporation of dietary long chain n−3 fatty acids into the brain phosphatidylcholine fraction was enhanced in the ethanol-treated animals; by day 32 the animals treated prenatally with ethanol also showed increased levels of long chain n−6 compounds. Behavioral development was retarded by ethanol, but there was no effect of the dietary oils. These results support the hypothesis that effects of ethanol on the developing brain may be modified by the availability of an exogenous supply of long chain fatty acids.     

Comparison of growth and fatty acid metabolism in rats fed diets containing equal levels of γ-linolenic acid from high γ-linolenic acid canola oil or borage oil

We have utilized transgenic technology to develop a new source of γ-linolenic acid (GLA) using the canola plant as a host. The aim of the present study was to compare the growth and fatty acid metabolism in rats fed equal amounts of GLA obtained from the transgenic canola plant relative to GLA from the borage plant. Young male Sprague-Dawley rats (n=10/group) were randomized and fed a purified AIN93G diet (10% lipid by weight) containing either a mixture of high GLA canola oil (HGCO) and corn oil or a control diet containing borage oil (BO) for 6 wk. GLA accounted for 23% of the triglyceride fatty acids in both diets. Growth and diet consumption were monitored every 2–3 d throughout the study. At study termination, the fatty acid composition of the liver and plasma phospholipids was analyzed by gas chromatography. The growth and diet consumption of the HGCO group were similar to the BO group. There were no adverse effects of either diet on the general health or appearance of the rats, or on the morphology of the major organs. There was no significant difference between the diet groups for total percentage of n−6 polyunsaturated fatty acids present in either the total or individual phospholipid fractions of liver or plasma. The relative percentage of GLA and its main metabolite, arachidonic acid, in each phospholipid fraction of liver or plasma were also similar between groups. The percentage of 18∶2n−6 in liver phosphatidylethanolamine and phosphatidylinositol/serine was higher (P<0.05) and 22∶5n−6 was lower in the HGCO group than the BO group. This finding could be attributed to the higher 18∶3n−3 content in the HGCO diet than the BO diet. Results from this long-term feeding study of rats show for the first time that a diet containing transgenically modified canola oil was well-tolerated, and had similar biological effects, i.e., growth characteristics and hepatic metabolism of n−6 fatty acids, as a diet containing borage oil.     

Effects of dietary n−3 polyunsaturated fatty acids on phospholipid composition and calcium transport in mouse cardiac sarcoplasmic reticulum

The effects of dietary n−3 and n−6 polyunsaturated fatty acids on the fatty acid composition of phospholipid, Ca⁺⁺· Mg⁺⁺ ATPase and Ca⁺⁺ transport activities of mouse sarcoplasmic reticulum were investigated. Mice were fed a 2 weight percent fat diet containing either 0.5 weight percent ethyl esters of 18∶3n−3, 20∶5n−3 or 22∶6n−3 as a source of n−3 polyusaturated fatty acid or 0.5 weight percent safflower oil as a cource of n−6 polyunsaturated fatty acid for 10 days. Olive oil (2 weight percent) was used as a control diet. Although feeding n−6 polyunsaturated fatty acid induced very little modifications of the phospholipid sarcoplasmic reticulum fatty acid composition, feeding n−3 polyunsaturated fatty acid altered it markedly. Inclusion of 18∶−3, 20∶5n−3 or 22∶6n−3 in the diet caused an accumulation of 22∶6n−3, which replaced 20∶4n−6 and 18∶2n−6 in phospholipid sarcoplasmic reticulum. The saturated fatty acids were significantly increased with a concurrent reduction of 18∶1n−9. These changes in the fatty acid composition resulted in a decrease in the values of the n−6/n−3 polyunsaturated fatty acid ratio and a decrease in the ratio of 20 carbon to 22 carbon fatty acids esterified in the phospholipid sarcoplasmic reticulum. This was associated with a decrease in Ca⁺⁺ uptake by n−3 polyunsaturated fatty acid enriched sarcoplasmic reticulum vesicles as compared with n−6 fatty acid and control diet sarcoplasmic reticulum vesicles. However, neither the affinity for Ca⁺⁺ nor the maximal velocity of ATP hydrolysis activity of Ca⁺⁺·MG⁺⁺ ATPase were altered by the different diets. The data suggest that the incorporation of 22∶6n−3 and/or the decrease of 20∶4n−6 plus 18∶2n−6 in the phospholipid sarcoplasmic reticulum may affect the membrane lipid bilayer structure and make it more permeable to Ca⁺⁺.     

Modulation of cyclic nucleotide phosphodiesterase by dietary fats in rat heart

Feeding oils of different fatty acid composition modifies the fatty acid composition of cardiac membrane phospholipids, thereby inducing changes in cardiac contractility and altering response of adenylate cyclase to catecholamines. In the present study, the effect of such dietary manipulations on cyclic nucleotide phosphodiesterase, which is involved in the control of cyclic nucleotide intracellular levels and in the control of cardiac contractility, was investigated. Rats were fed either a saturated fatty acid-enriched diet (8 weight percent [%] coconut oil +2% sunflower oil), an n−6 fatty acid-enriched diet (10% sunflower oil) or an n−3 fatty acid-enriched diet (8% fish oil +2% sunflower oil). The fatty acid composition of cardiac phospholipids, as well as the nonesterified fatty acid content of heart were markedly altered by the diets. The 18∶2n−6 and 20∶4n−6 content of cardiac phospholipids was markedly (−49%) depressed by fish oil as compared with sunflower oil feeding, but the nonesterified fatty acid level of heart membrane was lowest in coconut oil-fed rats. In addition, fish oil feeding more drastically depressed the n−6/n−3 fatty acid ratio in the nonesterified fatty acid pool than in cardiac phospholipids. Cyclic AMP phosphodiesterase activity was the lowest in both the particulate and soluble fractions of heart from rats fed sunflower oil, whereas cyclic GMP phosphodiesterase activity was not altered by the diets. Cyclic AMP phosphodiesterase activity was decreased by 18 and 12% in heart membranes of the sunflower oil group as compared to that of the coconut oil and fish oil groups, respectively. In heart cytosol, the activity decreased by 30% when compared with the activity of the coconut oil group. Additionalin vitro experiments showed that polyunsaturated fatty acids were more potent inhibitors of cyclic AMP phosphodiesterase than saturated fatty acids. These results suggest that polyunsaturated fatty acid-enriched diets might decrease heart cyclic AMP phosphodiesterase activity by increasing non-esterified polyunsaturated fatty acids, especially those of the n−6 series, but more complex and indirect mechanisms are very likely to be involved.     

Alteration in mouse splenic phospholipid fatty acid composition and lymphoid cell populations by dietary fat

The fatty acid composition of diacyl- and alkylacylglycerophosphocholine (PC), phosphatidylinositol (PI), phosphatidylserine (PS), alkenylacyl-glycerophosphoethanolamine (aPE), and diacyl- and alkylacyl-glycerophosphoethanolamine (dPE) was assessed in isolated splenocytes from C3H/Hen mice fed one of four purified isocaloric diets for six weeks. Diets contained 20% by weight of either a high-linoleate sunflower oil (Hi 18∶2), a high-oleate sunflower oil (Hi 18∶1), a mixture of 17% menhaden fish oil and 3% high-linoleate sunflower oil (Hi n−3), or a mixture of 17% coconut oil and 3% high-linoleate sunflower oil (Hi SFA). Spleen weight and immune cell yield were significantly higher (P<0.05) in mice fed the Hi 18∶1 or the Hi n−3 diets compared with those fed the Hi 18∶2 and Hi SFA diets. Distinctive patterns of fatty acids were observed for each phospholipid in response to dietary fatty acids. Dietary fat significantly affected (P<0.05) total polyunsaturated fatty acids (PUFA) in PC and dPE, total saturated fatty acids (SFA) in PC, total monounsaturated fatty acids (MUFA), and n−3 PUFA in all phospholipid classes examined. In mice fed the Hi n−3 diet, n−3 PUFA were significantly elevated, whereas n−6 PUFA decreased in all of the phospholipids. In these mice, eicosapentaenoic acid (EPA) was the predominant n−3 PUFA in PC and PI, whereas docosahexaenoic acid (DHA) was the major n−3 PUFA in aPE and PS. Interestingly, the ratios of n−3/n−6 PUFA in the phospholipids from these mice were 3.2, 2.4, 1.8, 0.8 and 0.8 for aPE, PS, dPE, PC and PI, respectively. These data suggest a preferential incorporation of n−3 PUFA into aPE, PS and dPE over PC and PI.     

Dietary cod liver oil decreases arachidonic acid in rat gastric mucosa and increases stress-induced gastric erosions

The purpose of this study was to examine the influence of long-term feeding of dietary fat rich in either n−3 or n−6 fatty acids on the availability of arachidonic acid (20∶4n−6) in major phospholipids of gastric mucosa in rats. Three groups of male Wistar rats were fed either a standard diet, a cod liver oil-enriched diet (10% by weight), or a corn oil-enriched diet (10% by weight) for 8 mon. Dietary cod liver oil significantly reduced the level of 20∶4n−6 in phosphatidylcholine (PC) and in phosphatidylethanolamine (PE) of gastric mucosa. The loss of 20∶4n−6 was compensated for by eicosapentaenoic acid (20∶5n−3) in PC, whereas the decrease in 20∶4n−6 in PE corresponded to the increase in three n−3 fatty acids: 20∶5n−3, docosapentaenoic acid (22∶5n−3), and docosahexaenoic acid (22∶6n−3). The level of 20∶5n−3 was higher than the level of 22∶6n−3 both in PC and PE of mucosa in rats fed cod liver oil. Diets supplemented with corn oil increased the level of 18∶2n−6 but decreased the monoene fatty acids 16∶1 and 18∶1n−7 in PC but not in PE of gastric mucosa. The 20∶4n−6 levels of both PC and PE were markedly reduced by dietary cod liver oil, to about one-third of control levels. Similar changes were also observed in the stomach wall. Gastric erosions were observed in all rats exposed to restriction stress, but this form of stress induced twice the number of erosions in rats fed fish oil compared to control rats or rats fed corn oil. We conclude that a diet rich in fish oil altered the balance between n−6 and n−3 fatty acids in major gastric mucosal phospholipids, markedly reduced the availability of 20∶4n−6, and increased the incidence of gastric erosions induced by restriction or emotional stress.     

Hematological and lipid changes in newborn piglets fed milk replacer diets containing vegetable oils with different levels of n−3 fatty acids

To test if linolenic acid (18∶3n−3) from vegetable oils would affect bleeding times and platelet counts in new-borns, piglets were used as a model fed milk replacer diets containing 25% (by wt) vegetable oils or oil mixtures for 28 d and compared to sow-reared piglets. The oils tested included soybean, canola, olive, high oleic sunflower (HOAS), a canola/coconut mixture and a mixture of oils mimicking canola in fatty acid composition. All piglets fed the milk replacer diets showed normal growth. Bleeding times increased after birth from 4–6 min to 7–10 min by week 4 (P<0.001), and were higher in pigs fed diets containing 18∶3n−3, as well as in sowreared piglets receiving n−3 polyunsaturated fatty acids (PUFA) in the milk, as compared to diets low in 18∶3n−3. Platelet numbers increased within the first week in newborn piglets from 300 to 550×10⁹/L, and remained high thereafter. Milk replacer diets, containing vegetable oils, generally showed a transient delay in the rise of platelet numbers, which was partially associated with an increased platelet volume. The oils showed differences in the length of delay, but by the third week of age, all platelet counts were >500×10⁹/L. The delay in rise in platelet counts appeared to be related to the fatty acid composition of the oil, as the effect was reproduced by a mixture of oils with a certain fatty acid profile, and disappeared upon the addition of saturated fatty acids to the vegetable oil. There were no alterations in the coagulation factors due to the dietary oils. Blood plasma, platelets and red blood cell membranes showed increased levels of 18∶3n−3 and long-chain n−3 PUFA in response to dietary 18∶3n−3. The level of saturated fatty acids in blood lipids was generally lower in canola and HOAS oil-fed piglets as compared to piglets fed soybean oil or reared with the sow. The results suggest that consumption of milk replacer diets containing vegetable oils rich in 18∶3n−3 does not represent a bleeding risk, and that the transient lower platelet count can be counterbalanced by the addition of saturated fatty acids to the vegetable oils.     

Lipid metabolism and FA composition in tissues of Eurasian perch Perca fluviatilis as influenced by dietary fats

Eurasian perch, Perca fluviatilis, were fed a semipurified fat-free diet for 4 wk, followed by a 16% feeding supplementation of either olive oil (OO), safflower oil (SO), linseed oil (LO), or cod liver oil (CLO) as the only lipid source in each diet for 10 wk. Significant reductions in total lipid of tissues were observed (31.4% in viscera, 66.7% in muscle, and 74.1% in liver) after feeding the fat-free diet. The SO-, LO-, and CLO-fed fish significantly increased lipid deposition in liver and viscera compared to fish fed the OO diet; however, muscle lipid levels were not significantly affected. Large amounts of dietary 18∶1n−9 were incorporated directly into tissue lipids when fish were fed the OO diet. The LO diet significantly elevated 18∶4n−3, 20∶5n−3, 22∶5n−3, and 22∶6n−3 in the liver compared to fish fed OO or SO diets, and the n−3/n−6 ratio was 16 times that of the SO group, with significantly high desaturation and elongation products of 18∶3n−3. These results suggest that Δ6 and Δ5 desaturases are highly active in Eurasian perch, and that the enzymes at this dietary n−3/n−6 ratio favor 18∶3n−3 over 18∶2n−6 as substrate. The SO diet significantly increased 18∶3n−6, 20∶3n−6, and 22∶5n−6 in the liver and significantly decreased EPA and DHA. This indicates that desaturation enzymes were not specifically favoring n−3 over n−6 acids in perch lipid metabolism, and that these elongation and desaturation enzymes were influenced by n−3 and n−6 FA content in the diet. The present study indicates that high tissue content of DHA in the muscle of Eurasian perch was attributable to the greater ability for n−3 acid bioconversion.     

Effect of low levels of dietary fish oil on fatty acid desaturation and tissue fatty acids in obese and lean rats

The effect of very low levels of dietary long-chain n−3 fatty acids on Δ6 desaturation of linoleic acid (18∶2n−6) and α-linolenic acid (18∶3n−3), and on Δ5 desaturation of dihomo-γ-linolenic acid (20∶3n−6), in liver microsomes and its influence on tissue fatty acids were examined in obese and lean Zucker rats and in Wistar rats. Animals fed for 12 wk a balanced diet containing ca. 200 mg of long-chain polyunsaturated n−3 fatty acids per 100 g of diet were compared to those fed the same amount of α-linoleic acid. Low amounts of long-chain n−3 fatty acids greatly inhibited Δ6 desaturation of 18∶2n−6 and Δ5 desaturation of 20∶3n−6, while Δ6 desaturation of 18∶3n−3 was not inhibited in Zucker rats and was even stimulated in Wistar rats. Inhibition of the biosynthesis of long-chain n−6 fatty acids was reflected in a decrease in arachidonic acid (20∶4n−6) content of serum lipids when fasting, and also in the phospholipid fatty acids of liver microsomes. On the contrary, heart and kidney phospholipids did not develop any decrease in 20∶4n−6 during fish oil ingestion. Docosahexaenoic acid (22∶6n−3), present in the dietary fish oil, was increased in serum lipids and in liver microsome, heart, and kidney phospholipids.     

Paradoxical effect of n−3-containing vegetable oils on long-chain n−3 fatty acids in rat heart

Flaxseed, echium, and canola oils contain α-linolenic acid (18∶3n−3, ALA) in a range of concentrations. To examine their effect on elevating cardiac levels of long-chain n−3 FA, diets based on these n−3-containing vegetable oils were fed to rats for 4 wk. Sunflower oil, which contains little ALA, was a comparator. Despite canola oil having the lowest ALA content of the three n−3-containing vegetable oils, it was the most potent for elevating DHA (22∶6n−3) levels in rat hearts and plasma. However, the relative potencies of the dietary oils for elevation of EPA (20∶5n−3) in heart and plasma followed the same rank order as their ALA content, i.e., flaxseed>echium>canola>sunflower oil. This paradox may be explained by lower ALA intake leading to decreased competition for Δ6 desaturase activity between ALA and the 24∶5n−3 FA precursor to DHA formation.     

The effect of dietary linoleic acid on the fatty acid composition of individual phospholipid and lipoxygenase products from gills and leucocytes of Atlantic salmon (Salmo salar)

Diets containing either fish oil or sunflower oil, both of which supplied the minimum required level of n−3 fatty acids, were given to Atlantic salmon (Salmo salar) postsmolts for a period of 16 weeks. In fish fed sunflower oil, the phospholipids of gills showed increased 18∶2n−6 (2–13-fold), 20∶2n−6 (4.5–12-fold) and 20∶−6 (2–8-fold). In addition, phosphatidylethanolamine had increased 20∶4n−6 (1.5-fold). Changes of a similar magnitude were observed in the phospholipids of blood leucocytes except that, in addition, 20∶4n−6 was elevated in phosphatidylserine (1.7-fold) and phosphatidylinositol (1.4-fold). Both tissues showed a general decrease in phospholipid 20∶5n−3 (up to 3-fold), which caused an increase in 20∶4n−6/20∶5n−3 ratio (1.3–6-fold). The elongation and desaturation products of 20∶4n−6, 22∶4n−6 and 22∶5n−6 were not increased as a result of feeding sunflower oil. When isolated gill cells were stimulated with the calcium ionophore A23187, 12-hydroxy-8,10,14,17-eicosapentaenoic acid (12-HEPE) was the major lipoxygenase product from salmon given fish oil. 12-HEPE was significantly reduced in salmon given sunflower oil. When stimulated with A23187, the lipoxygenase products derived from whole blood of fish given sunflower oil showed decreased levels of leukotriene B₅, 12-HEPE and 12-hydroxy-5,8,10,14-eicosatetraenoic acid.     

Dietary manipulation of long-chain polyunsaturated fatty acids in the retina and brain of guinea pigs

High levels of n−6 docosapentaenoic acid (22∶5n−6) have been reported in the retina of guinea pigs fed commercially-prepared grain-based rations (commercial diet). In rats and monkeys, high levels of 22∶5n−6 are an indicator of n−3 polyunsaturated fatty acid (PUFA) deficiency. We have examined the fatty acid composition of the retina and brain in guinea pigs fed a commercial diet or one of three semi-purified diets containing three different levels of n−3 PUFA. The diets comprised a diet deficient in n−3 PUFA (semi-purified diet containing safflower oil), two diets containing α-linolenic acid (standard commercial laboratory diet and semi-purified diet containing canola oil), and a diet containing α-linolenic acid, eicosapentaenoic acid, and docosahexaenoic acid (DHA) (semi-purified diet containing canola oil, safflower oil, and fish oil). Two groups of guinea pigs were given the diets from day 1 to 4 wk or day 1 to 8 wk, when they were sacrificed and the retinal tissues were extracted and analyzed for PUFA content by gas-liquid chromatography. Fatty acid analyses of the retinal phospholipids of the four-week-old animals revealed that the group fed DHA (from the fish oil) had the highest level of DHA (32%), compared with values of 19 and 13% for the groups fed canola oil diet and commercial diet, respectively, and 2% for the group fed the diet deficient in n−3 PUFA. The levels of 22∶5n−6 in the retinal lipids were inversely related to the DHA values, being 0.6, 6.6, 11.4, and 20.6 for the fish oil, canola oil, commercial diet, and safflower oil diet groups, respectively. The long-chain PUFA profiles in the brain phospholipids of the four-week-old group were similar to those from the retina. The retinal PUFA values for the eight-week-old animals were similar to the four-week-old group. The safflower oil diet induced a greater deficit of DHA in retinal lipids than has been reported in rats and monkeys fed similar diets. The guinea pigs fed the commercial diet had retinal and brain PUFA patterns similar to that produced by n−3 PUFA-deficient diets in rats and monkeys. Guinea pigs fed the canola oil diet had significantly greater retinal DHA levels than those fed the commercial diet, but lower than those fed fish oil. The data suggest that the guinea pig has a reduced capacity for DHA synthesis from α-linolenic acid as compared with other mammals. Supplementation of guinea pig diets with fish oil produced high retinal and brain DHA levels and prevented the accumulation of 22∶5n−6.     

Incorporation of n−3 fatty acids into plasma and liver lipids of rats: Importance of background dietary fat

The health benefits of long-chain n−3 PUFA (20∶5n−3 and 22∶6n−3) depend on the extent of incorporation of these FA into plasma and tissue lipids. This study aimed to investigate the effect of the background dietary fat (saturated, monounsaturated, or n−6 polyunsaturated) on the quantitative incorporation of dietary 18∶3n−3 and its elongated and desaturated products into the plasma and the liver lipids of rats. Female weanling Wistar rats (n=54) were randomly assigned to six diet groups (n=9). The fat added to the semipurified diets was tallow (SFA), tallow plus linseed oil (SFA-LNA), sunola oil (MUFA), sunola oil plus linseed oil (MUFA-LNA), sunflower oil (PUFA), or sunflower oil plus linseed oil (PUFA-LNA). At the completion of the 4-wk feeding period, quantitative FA analysis of the liver and plasma was undertaken by GC. The inclusion of linseed oil in the rat diets increased the level of 18∶3n−3, 20∶5n−3, and, to a smaller degree, 22∶6n−3 in plasma and liver lipids regardless of the background dietary fat. The extent of incorporation of 18∶3n−3, 20∶5n−3, and 22∶5n−3 followed the order SFA-LNA>MUFA-LNA>PUFA-LNA. Levels of 22∶6n−3 were increased to a similar extent regardless of the type of major fat in the rat diets. This indicates that the background diet affects the incorporation in liver and plasma FA pools of the n−3 PUFA with the exception of 22∶6n−3 and therefore the background diet has the potential to influence the already established health benefits of long-chain n−3 fatty acids.