Effects of dietary saturated, n-6 and n-3 polyunsaturated fats on blood pressure and prostaglandins outflow from perfused mesenteric vascular bed in rats

Effects of the dietary administration of saturated fat and of n-6 and n-3 polyunsaturates on blood pressure, prostaglandin metabolism in small vessels, tissue fatty acid distribution and urinary PGE₂ excretion were compared. Rats were divided into three groups. Diets contained 10% hydrogenated cocunut oil (HCO), 10% safflower oil (SFO) or 10% cod liver oil (CLO) added to a basic fat free diet for 10 weeks. Systolic blood pressure was increased in the CLO group animals. Urinary PGE₂ excretion was decreased in the HCO and CLO groups as compared to that in the SFO group animals. PGE₂, 6-keto-PGF₁ and thromboxane (Tx) B₂ outflow from isolated perfused mesenteric arterial beds were extremely decreased in the CLO group animals, and to a lesser extent in the HCO group as compared to the SFO animals. In the tissue phospholipid, 20:3n−9/20:4n−6 ratios were increased in the HCO group indicating essential fatty acid deficiency, and n-6 and n-3 polyunsaturates were elevated in the SFO and the CLO group animals respectively. Arachidonic acid concentration was highest in the SFO group, while there was no significant differences between the HCO and the CLO group. These results suggest that dietary fatty acid manipulation effects urinary PGE₂ excretion and PGI₂, PGE₂ and TxA₂ synthesis in mesenteric arterial beds and also changes the tissue fatty acid distribution. Furthermore, n-3 polyunsaturates caused an extreme reduction of 2-series PGs synthesis in small resistance vessels.     

The effect of chemical hepatocarcinogenesis on liver phospholipid composition in rats fed N-6 and N-3 fatty acid-supplemented diets.

The effect of dietary fats on essential fatty acid metabolism in rats subjected to chemically induced hepatocarcinogenesis was studied. Sixty male rats were fed a diet supplemented with one of the following three oil compositions: 10% hydrogenated coconut oil (HCO); 5% hydrogenated coconut oil and 5% gamma-linolenic acid (18:3n-6)-rich evening primrose oil (EPO); or 5% hydrogenated coconut oil and 5% marine oil (FO). Half of the animals in each dietary regimen were subjected to hepatocarcinogenesis induction using diethylnitrosamine and 2-acetylaminofluorene (2-AAF) followed by partial hepatectomy, whereas the other half underwent hepatectomy without receiving diethylnitrosamine and 2-acetylaminofluorene. Liver phospholipid composition was analyzed. In comparison to the HCO group, the EPO group showed raised levels of arachidonic acid (20:4n-6) and suppressed n-3 fatty acids. The FO group, on the other hand, showed suppressed levels of n-6 and increased n-3 fatty acids. Hepatocarcinogenesis suppressed the level of 20:4n-6 and this effect was greater in the FO rats. The levels of dihomo-gamma-linolenic acid (20:3n-6) were increased by the hepatocarcinogenic treatment, and this effect was further accentuated in the EPO rats. These results suggest that hepatocarcinogenesis may suppress the activity of delta-5-desaturase, which may be one of the reasons why tumor cell membranes have low levels of long chain fatty acids, especially 20:4n-6 cells, and have an impaired capacity to undergo lipid peroxidation.     

Fatty acid changes in liver choline and ethanolamine glycerophospholipids in aspirin-treated rats fed linoleate, gamma-linolenate and fish oil

The effects of dietary linoleic acid, gamma-linolenic acid and marine fatty acids on the development of aspirin-induced gastric hemorrhage and the distribution of liver glycerophospholipid fatty acids in fat-deficient growing rats were studied. Aspirin (100 mg/day)-treated and nontreated rats were fed for 7 days, a mixed diet of 2.5% safflower oil and 7.5% hydrogenated coconut oil (SFO/HCO) or 7.5% fish oil (SFO/FO), or 2.5% gamma-linolenate concentrate and 7.5% fish oil (GLA/FO). Gastric hemorrhage was induced in animals by aspirin treatment to various extents. It was not affected by FO feeding, but was significantly alleviated by GLA feeding. Aspirin treatment reduced the proportions of 20:4n-6 in liver phosphatidylcholine. FO feeding (in SFO/FO and GLA/FO rats) further reduced the 20:4n-6 level and replaced it by n-3 fatty acids. GLA feeding, on the other hand, elevated the proportion of 20:4n-6. As a result, the reduction of 20:4n-6 by fish oil feeding, was less significant in GLA/FO rats than in SFO/FO rats. The degree of gastric hemorrhage appeared to relate negatively to the levels of 20:4n-6 in liver phosphatidylcholine, and to the sum of 20:4n-6 and 20:5n-3 when FO was included in the diet. It is suggested that long-chain polyunsaturated fatty acids (20:4n-6 and 20:5n-3) per se in addition to being precursors of prostaglandins, may also affect the development of gastric hemorrhage, possibly by modulating the permeability of cell membranes in the gastric mucosa.     

The effects of hydrogenated coconut oil, safflower oil, and evening primrose oil on development of hypertension and sodium handling in spontaneously hypertensive rats

Spontaneously hypertensive rats (SHR) were fed a basal regular diet (BD) or three different fat-supplemented diets which contained 10% hydrogenated coconut oil (HCO), 10% safflower oil (SFO), or 10% evening primrose oil (EPO). The rats received these four different diets from 4 weeks to over 24 weeks of age. The development of hypertension in SHR was significantly retarded in the EPO-supplemented animals. The blood pressure was lower in the SFO group animals as compared with the BD and HCO groups, but this did not reach significance. Sodium excretion rate in young SHR was increased in the EPO group compared with the HCO and SFO groups, and the urinary K/Na ratio was decreased in the EPO group compared with the HCO and EPO groups. Water intake and urine volume were increased in the SFO group as compared with the HCO and EPO groups. Sodium concentration in erythrocytes was decreased in the rats receiving SFO. Pressor responses to norepinephrine and angiotensin II were enhanced in the EPO and SFO groups as compared with the basal chow group. These data suggest that a dietary supplementation of EPO which contains a substantial amount of gamma-linolenic acid consistently lowers blood pressure in SHR. The mechanism is uncertain, but the effects on sodium handling may in part be responsible for the retardation of the development of hypertension. There was a difference between the EPO and the SFO groups in sodium--water handling, and to some extent in the blood pressure development in SHR.     

Bio-availability and metabolism of n-3 fatty acid rich garden cress (Lepidium sativum) seed oil in albino rats

The ratio of fatty acids namely linoleic acid (LA, 18:2, n-6) and alpha linolenic acid (ALA, 18:3, n-3) in the diet plays an important role in enrichment of ALA in tissues and further conversion to long-chain polyunsaturated fatty acids (LC-PUFA) like eicosapentaenoic acid (EPA, 20:5, n-3) and docosahexaenoic acid (DHA, 22:6, n-3). Garden cress seed oil (GCO) is one of the richest sources of omega-3 fatty acid and contains 29-34.5% of ALA. In this study, dietary supplementation of GCO on bio-availability and metabolism of alpha-linolenic acid was investigated in growing rats. Male wistar rats were fed with semi-purified diets supplemented with 10.0% sunflower oil (SFO 10%); 2.5% GCO and 7.5% SFO (GCO 2.5%); 5% GCO and 5% SFO (GCO 5.0%); 10% GCO (GCO 10%) for a period of 8 weeks. There was no significant difference with regard to the food intake, body weight gain and organ weights of rats in different dietary groups. Rats fed with GCO showed significant increase in ALA levels in serum and tissues compared to SFO fed rats. Feeding rats with 10% GCO lowered hepatic cholesterol by 12.3% and serum triglycerides by 40.4% compared to SFO fed group. Very low density lipoprotein cholesterol (VLDL-C) and low density lipoprotein cholesterol (LDL-C) levels decreased by 9.45% in serum of 10% GCO fed rats, while HDL remained unchanged among GCO fed rats. Adipose tissue showed incorporation of 3.3-17.4% of ALA and correlated with incremental intake of ALA. Except in adipose tissue, the EPA, DHA levels increased significantly in serum, liver, heart and brain tissues in GCO fed rats. A maximum level of DHA was registered in brain (11.6%) and to lesser extent in serum and liver tissues. A significant decrease in LA and its metabolite arachidonic acid (AA) was observed in serum and liver tissue of rats fed on GCO. Significant improvement in n-6/n-3 fatty acid ratio was observed in GCO based diets compared to diet containing SFO. This is the first study to demonstrate that supplementation of GCO increases serum and liver ALA, EPA, DHA and decreases LA and AA in rats. Therefore, the GCO can be considered as a potential, alternate dietary source of ALA.     

Dietary manipulation with high marine fish oil intake of fatty acid composition and arachidonic acid metabolism in rat cerebral microvessels

Male weanling Wistar rats were maintained on one of two semisynthetic diets, differing only in the type of oil used: (i) 10% by weight marine fish oil (MFO group) containing 20% eicosapentaenoic acid (EPA) and 17% docosahexaenoic acid (DHA), or (ii) 10% by weight sunflower oil (SFO group). The control group was kept on standard diet for 4 weeks. Blood-free microvessels were isolated from brain cortex by a rapid micromethod, and their fatty acid composition was determined by gas chromatography. It was found that the proportion of n-3 fatty acids (including EPA and DHA) increased significantly in the microvessels of the MFO group, accompanied by a decrease of the n-6 fatty acid series. The changes in fatty acid composition of endothelial cells were not significant in the SFO group in comparison to the control. The amounts of lipoxygenase and cyclooxygenase metabolites were determined. Dietary fish oil decreased the percentage of total products of arachidonate by 50%, while the SFO diet had no effect on it. The amount of lipoxygenase products in the MFO group decreased significantly from 16931±3131 dpm to 6399±357 dpm/300 mg wet weight of brain. Significantly less PGF-1, PGF-2 and 12-hydroxyhepta-decatrienoic acid (HHT) were found in the capillaries of MFO treated animals, in comparison to the SFO group. The ratios of vasoconstrictor and vasodilator metabolites of arachidonate cascade were not modifed by the diets. Our results suggest that fish oil diet reduces the arachidonate cascade in cerebral microvessels. This effect may explain for the efficiency of n-3 fatty acids in vascular diseases.     

The effect of dietary fish oils on eicosanoid biosynthesis in peritoneal macrophages is influenced by both dietary N-6 polyunsaturated fats and total dietary fat

Recent research has implicated dietary fish oils in the reduction of eicosanoids formed from arachidonic acid and amelioration of chronic diseases such as coronary heart disease, atherosclerosis and inflammation. Feeding studies were conducted to determine if the efficacy of dietary n-3 polyunsaturated fatty acids (PUFA) from fish oils was influenced by the quantity of n-6 polyunsaturated fatty acids and the total level of fat in the diet. Groups of mice were fed diets composed of 5 and 20% total fat with varying proportions of linoleic acid as a source of n-6 PUFA. Menhaden oil as a source of n-3 PUFA was fed at two levels of n-6 at each level of total fat. Eicosanoid biosynthesis was stimulated and assayed in the mouse peritoneum using zymosan as an inflammatory stimulus. Production of LTE4 and PGE2 was enhanced by increasing n-6 PUFA in the diet at both levels of total fat. High dietary fat significantly suppressed leukotriene (LT) synthesis. Dietary menhaden oil reduced LTE4 and PGE2 synthesis at both levels of dietary n-6 in the low fat study. In animals on 20% dietary fat menhaden oil significantly reduced LT synthesis only at a relatively low dietary n-6 PUFA. On a high n-6 PUFA high fat diets, menhaden oil did not significant affect LTE4 synthesis in response to zymosan stimulation. The results suggest that the effectiveness of fish oils in reducing eicosanoids in response to specific stimulation is influenced by the level of n-6 and the total quantity of fat in the diet.     

N-3 HUFAs affect fat deposition,susceptibility to oxidative stress,and apoptosis in Atlantic salmon visceral adipose tissue

We have investigated how n-3 highly unsaturated fatty acids (HUFAs) in the diet affect fatty acid (FA) utilization, fat storage and oxidative stress (OS) in Atlantic salmon (Salmo salar) white adipose tissue (WAT). Four groups of Atlantic salmon were fed for 21 weeks on one of the four diets supplemented with 23% (of dry matter) lipid. Docosahexaenoic acid (DHA; 22:6n-3) and eicosapentaenoic acid (EPA; 20:5n-3) levels increased from 10% of total FAs in the rapeseed oil (RO) diet, to 20% in the fish oil (FO) diet, and to 50% and 55% in the DHA-enriched and EPA-enriched diets, respectively. Increased dietary levels of n-3 HUFAs resulted in lower fat percentage in WAT. Furthermore, mitochondrial FA β-oxidation activity was higher in the FO group than it was in the RO group. The relative levels of DHA and EPA in phospholipids (PLs) from WAT and mitochondrial membranes increased with the increasing dietary levels of these HUFAs. In general, the mitochondrial membrane PLs were characterised by lower relative levels of n-3 HUFAs and higher relative levels of linoleic acid (LA; 18:2 n-6) than WAT membrane PLs. The predominance of LA relative to n-3 HUFAs in mitochondrial membrane PLs may help to protect these PLs from peroxidation. Cytochrome c oxidase measurements revealed higher incidence of disrupted mitochondrial membranes in the DHA and EPA dietary groups than in the FO and RO dietary groups. This disruption further affected the mitochondrial function, resulting in a marked reduction in FA β-oxidation capacities. The reduction in mitochondrial function and the increase in the activity of superoxide dismutase (SOD) in the DHA and EPA groups showed that high dietary dose of DHA and EPA resulted in oxidative stress (OS). The increased activity of caspase 3 in the high n-3 HUFA groups suggested the induction of apoptosis and increased incidence of cell death in WAT, which may be one of the factors explaining the lower fat percentage found in these groups.     

Maternal dietary n-3 fatty acids alter cardiac ventricle fatty acid composition, prostaglandin and thromboxane production in growing chicks

The effects of feeding n-6 and n-3 fatty acids to broiler hens on cardiac ventricle fatty acid composition, and prostaglandin E2 (PGE2) and thromboxane A2 (TXA2) production of hatched chicks were investigated. Fertile eggs obtained from hens fed diets supplemented with 3.5% sunflower oil (Low n-3), 1.75% sunflower+1.75% fish oil (Medium n-3), or 3.5% fish oil (High n-3) were incubated. The hatched chicks were fed a diet containing 18:3 n-3, but devoid of longer chain n-6 and n-3 fatty acids for 42 days. Arachidonic acid content was lower in the cardiac ventricle of High n-3 and Medium n-3 compared to Low n-3 birds for up to 2 weeks (P<0.002). Long chain n-3 fatty acids were higher in the cardiac ventricle of chicks from hens fed High and Medium n-3 diets when compared to chicks from hens fed the Low n-3 diet. Differences in long chain n-3 fatty acids persisted up to four weeks of age (P<0.001). Peripheral blood mononuclear cells (PBMNC) of 7-day-old High n-3 broilers produced significantly lower PGE2 and TXA2 than PBMNC from Low n-3 and Medium n-3 birds. These results indicate that maternal dietary n-3 fatty acids increases cardiac ventricle n-3 fatty acids while reducing arachidonic acid and ex vivo PGE2 and TXA2 production during growth in broiler chickens.     

The prostaglandin outflow from perfused mesenteric vasculature of rats fed different fats

The effects of dietary n-6 polyunsaturated fatty acids and replacement with saturated fat or fish oil on the prostaglandin outflow from perfused mesenteric vasculature in rats were studied. Seventy-two weanling male rats were fed ad libitum a semi-synthetic diet supplemented with 10% by weight of oil, composed wholly of n-6 fatty acid-rich evening primrose oil, or replaced partly or completely (25, 50, 75 or 100%) by n-6 fatty acid-deficient fish oil or hydrogenated coconut oil for 8 weeks. The outflows of 6-keto-PGF1 alpha, thromboxane B2, and prostaglandin E from the perfused mesenteric vasculature were measured at 60 min-time point after starting the perfusion. In general, the release of prostanoids from the mesenteric vasculature was significantly reduced in rats fed a diet in which evening primrose oil was partly or completely replaced by either hydrogenated coconut or fish oil. This was probably due to the insufficient conversion of linoleic acid to arachidonic acid. The extent of reduction was greater in fish oil-fed than in hydrogenated coconut oil-fed rats, while the levels of arachidonic acid in aortic phospholipids were similar between these two groups. This result implies that the greater reduction of prostaglandin synthesis in rats fed fish oil was due to the inhibitory effect of eicosapentaenoic and docosahexaenoic acids in fish oil on the conversion of arachidonate to eicosanoids.     

Influence of an increased intake of linoleic acid on the incorporation of dietary (n-3) fatty acids in phospholipids and on prostanoid synthesis in rat tissues.

We investigated whether the amount of dietary linoleic acid (LA) (as corn oil) influences the incorporation of dietary eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA) in tissue phospholipids and the prostanoid biosynthesis. Rats were fed four different levels of corn oil (at a total dietary fat level of either 2.5%, 5%, 10% or 20%); at each corn oil level, two groups of rats were supplemented with either EPA and DHA (200 mg/day) during 6 weeks, and compared with a group receiving oleic acid. The phospholipid fatty acid composition of liver, kidney and aorta showed, as expected, that the incorporation of EPA was highly suppressed by increasing the content of dietary linoleic acid in the diets. On the other hand, DHA was almost unaffected by the amounts of (n - 6) fatty acids in the diets. These results indicate that EPA levels but not DHA levels in tissue phospholipids were influenced by the competing dietary (n - 6) fatty acids. The tissue arachidonate content was similar under the various dietary linoleic acid conditions, but feeding EPA or DHA lowers the AA content. Moreover, the amount of dietary linoleic acid did not significantly influence the prostaglandin E2 (PGE2) production in stimulated aortic rings. However, PGE2 synthesis was significantly decreased in the groups treated with either EPA or DHA. Thromboxane B2 levels in serum followed a similar pattern. It is suggested that an increase of dietary (n - 3) PUFAs is more efficient to reduce (n - 6) eicosanoid formation than a decrease of dietary (n - 6) fatty acids.     

Gammalinolenic acid-enriched diet alters cutaneous eicosanoids

There are reports that vegetable oils containing gammalinolenic acid (GLA) may exert beneficial effects on inflammatory skin disorders. To determine whether or not dietary GLA exerts any modulatory role on cutaneous eicosanoids, guinea pigs were fed either a control diet containing safflower oil (less than 0.5% GLA) or borage oil, a GLA-rich diet containing 25% GLA. After an 8-week feeding period, epidermal samples from both animal groups were analyzed for fatty acid composition and tissue eicosanoids. Analysis of epidermal neutral lipids and phospholipids in borage oil-fed animals showed a marked increase in GLA and its elongase product, dihomogammalinolenic acid (DGLA). Similarly, analysis of epidermal eicosanoids in the borage oil-fed animals revealed significant increases in the amounts of the 15-hydroxy fatty acid (15-OH-20:3n-6) and prostaglandin PGE1, both metabolites of DGLA. Since these metabolites have anti-inflammatory potential, our results suggest that increased dietary GLA could result in the generation of local anti-inflammatory metabolites thus providing a non-toxic approach to suppression of cutaneous inflammatory skin disorders.     

Prostaglandins and thromboxane outflow from the perfused mesenteric vascular bed in spontaneously hypertensive rats

To clarify the metabolism of PGE2, prostacyclin (PGI2) and thromboxane A2 (TxA2) in small vessels in spontaneously hypertensive rats (SHR), we removed superior mesenteric vascular beds from 10 week old SHR and age matched normotensive controls (WKY). The mesenteric artery was perfused with Krebs-Henseleit buffer and samples of effluent collected every 15 minutes during 3 hours perfusion for analysis of PGE2, 6-keto-PGF1 alpha (a stable metabolite of PGI2) and TxB2 (a stable metabolite of TxA2) by specific radioimmunoassays. Levels of all three arachidonic acid (AA) metabolites, PGE2, 6-keto-PGF1 alpha and TxB2, in the mesenteric effluent were significantly reduced in SHR as compared to WKY. TxB2 was detected in all samples throughout the perfusion. 6-keto-PGF1 alpha/PGE2 ratios and TxB2/PGE2 ratios were significantly increased in SHR. 6-keto-PGF1 alpha/TxB2 ratios in the first four samples were significantly decreased in SHR as compared to WKY. These data suggest that there may be reduced availability of PG precusor AA and unbalanced synthesis of PGs in small vessels in SHR. Both may have relevance to the development of hypertension in the animals.     

Accumulation of N-3 Polyunsaturated Fatty Acids by Cultured Human Y79 Retinoblastoma Cells

Abstract: The metabolism of the n-3 class of polyunsaturated fatty acids, which occur in relatively high quantities in neural tissues, was studied in human Y79 retinoblastoma cells. These cells contained low levels of n-3 polyunsaturates when grown in culture media supplemented with fetal bovine serum. The cells readily incorporated preformed docosahexaenoic acid (22:6 n-3) into phospholipids, but human skin fibroblasts did this to a similar extent. When 10 to 30 μmol/ml linolenic acid (18:3 n-3) was added, the cells also accumulated 22:6 in phospholipids. The capacity to convert appreciable amounts of 18:3 to 22:6 appears to be a unique property of the retinoblastoma cells as compared with other continuously cultured cell lines. More 18:3 than linoleic acid (18:2 n-6) was incorporated into phospholipids by the retinoblastoma cultures, and 18:3 was channeled to a larger extent into the ethanolamine glycerophospholipid fraction. These findings indicate that retinoblastoma cells handle n-3 polyunsaturated fatty acids in a manner very similar to neural tissue in vivo . Based on the results obtained with this model system, it appears that three processes may contribute to the accumulation of 22:6 in retina and neural tissue: increased ability to incorporate 18:3, the capacity to convert 18:3 to 22:6, and channeling of 18:3 and its metabolites into ethanolamine glycerophospholipids.     

Changes in tissue fatty acid composition during the first month of growth of the king penguin chick

The switch from yolk to food (myctophid fishes) as the nutrient source for the newly hatched chick of the king penguin ( Aptenodytes patagonicus) results in a profound change in the pattern of fatty acid provision. This is characterized by major increases in the proportionate intake of n-3 polyunsaturates (20:5n-3 and 22:6n-3) and long chain (C(20-24)) monounsaturates, accompanied by relatively lower levels of n-6 polyunsaturates (18:2n-6 and 20:4n-6). The effects of this change on the fatty acid composition of tissue lipids during the first month of growth, a period of tissue maturation leading to thermal emancipation, were determined. The composition of adipose tissue triacylglycerol responded rapidly to the switch in nutrient source, the proportion of long chain monounsaturates (mainly 20:1n-9 and 22:1n-11) increasing five-fold between hatch and emancipation while the relative levels of 20:5n-3 and 22:6n-3 also increased significantly, by 3- and 1.2-fold, respectively. At emancipation, the fatty acid profile of adipose tissue triacylglycerol was essentially identical to that of the diet. At hatch, the main polyunsaturates of muscle phospholipid were 20:4n-6, 20:5n-3, and 22:6n-3, respectively, forming (w/w of fatty acids) 13.2%, 5.0%, and 12.0%. By emancipation, 20:4n-6 had decreased to 4.8%, 20:5n-3 increased to 10.9%, and 22:6n-3 at 11.4% showed little change. The main polyunsaturate in brain phospholipid at hatch was 22:6n-3 (19.3%): this remained almost constant until day 15 but then increased significantly to 23.6% by emancipation. Significant but minor changes in the proportions of 20:4n-6 (from 5.2% at hatch to 3.5% at emancipation) and 20:5n-3 (from 3.0% to 3.9%) were also observed in brain phospholipid. The data do not allow us to completely distinguish changes that are solely diet driven from those which are a consequence of tissue differentiation. Nevertheless, it is evident that, whereas the fatty acid composition of adipose tissue responds faithfully to the change in nutrient source, the phospholipids of muscle and, especially, of brain are much more refractory to the effects of diet during this period of tissue maturation.     

The effects of evening primrose oil, safflower oil and paraffin on plasma fatty acid levels in humans: Choice of an appropriate placebo for clinical studies on primrose oil

In a number of diseases, plasma levels of linoleic acid are normal or elevated while those of gamma-linolenic acid (18:3n-6, GLA) and further metabolites are below normal. Evening primrose oil (EPO), similar to safflower oil (SFO) except that it contains 8-9% of 18:3n-6, has been proposed as a therapeutic agent in these diseases, such as atopic eczema. There is argument as to whether an appropriate placebo for clinical studies on EPO should be an inert material such as paraffin, or a linoleic acid--containing oil such as SFO. We have therefore compared in normal humans the effects on plasma fatty acids of administering EPO, SFO and paraffin for 10 days. Paraffin had no effect on any fatty acid in any fraction. EPO raised the level of 20:3n-6 (dihomo-gamma-linolenic acid, DGLA) the immediate metabolite of GLA but had no significant effect on arachidonic acid. In surprising contrast, SFO raised the levels of linoleic and of arachidonic acids, without raising those of DGLA. This suggests that linoleic acid may be rapidly converted to arachidonic acid by a tightly linked enzyme sequence: GLA, in contrast, may be rapidly converted to DGLA but then only slowly on to arachidonic acid. These results are consistent with recent in vitro observations by others on rat hepatocytes and human fibroblasts.     

Cellular interactions between n-6 and n-3 fatty acids: a mass analysis of fatty acid elongation/desaturation, distribution among complex lipids, and conversion to eicosanoids.

The biologic effect of eicosanoids depends in large measure upon the relative masses in tissues of eicosanoids derived from the n-6 fatty acids, dihomogammalinolenic acid and arachidonic acid, and the n-3 fatty acid, eicosapentaenoic acid. Generation of this tissue balance is related to the relative cellular masses of these precursor fatty acids, the competition between them for entry into and release from cellular phospholipids, and their competition for the enzymes that catalyze their conversion to eicosanoids. In order to better understand these processes, we studied the cellular interactions of n-6 and n-3 fatty acids using an essential fatty acid-deficient, PGE-producing, mouse fibrosarcoma cell line, EFD-1. Unlike studies using cells with endogenous pools of n-6 and n-3 fatty acids, the use of EFD-1 cells enabled us to examine the metabolic fate of each family of fatty acids both in the presence and in the absence of the second family of fatty acids. Thus, the specific effects of one fatty acid family on the other could be directly assessed. In addition, we were able to replete the cells with dihomogammalinolenic acid (DHLA), arachidonic acid (AA), and eicosapentaenoic acid (EPA) of known specific activities; thus the masses of cellular DHLA, AA, and EPA, and their metabolites, PGE1, PGE2, and PGE3, respectively, could be accurately quantitated. The major findings of this study were: 1) n-6 fatty acids markedly stimulated the elongation of EPA to 22:5 whereas n-3 fatty acids inhibited the delta 5 desaturation of DHLA to AA and the elongation of AA to 22:4; 2) n-6 fatty acids caused a specific redistribution of cellular EPA from phospholipid to triacylglycerol; 3) n-3 fatty acids reduced the mass of DHLA and AA only in phosphatidylinositol whereas n-6 fatty acids reduced the mass of EPA to a similar extent in all cellular phospholipids; and 4) n-3 fatty acids caused an identical (33%) reduction in the bradykinin-induced release of PGE1 and PGE2, whereas n-6 fatty acids stimulated PGE3 release 2.3-fold. Together, these highly quantitative metabolic data increase our understanding of the regulation of both the cellular levels of DHLA, AA, and EPA, and their availability for eicosanoid synthesis. In addition, these findings provide a context for the effective use of these fatty acids in dietary therapies directed at modulation of eicosanoid production.     

Dietary n-3 Fatty Acids Inhibit Fever Induced by Inflammation in the Rat

Modification of endogenous eicosanoid synthesis by dietary n-3 fatty acid supplementation reduces febrile responses, but the mechanisms underlying these effects in vivo have not been determined. In the present study, local inflammation was induced by intramuscular injection ofturpentine in rats fed control or n-3 supplemented diets for 8-9 weeks. In animals fed the control diet, turpentine induced fever, hypermetabolism, marked local inflammation (oedema), increased plasma IL-6 concentrations and raised cerebrospinal fluid (CSF) concentrations of PGE2. N-3 fatty acid supplementation significantly inhibited the rise in CSF PGE2, fever and hypermetaboHsm induced by turpentine. Local inflammation and increased plasma IL-6 concentrations were not affected by n-3 supplementation. These findings suggest that modification of dietary fat intake inhibits fever via reduced release of prostaglandins, probably within the brain, but does not affect the local or afferent signals involved in fever generation.     

Effect of maternally supplied n-3 and n-6 oils on the fatty acid composition and mononuclear immune cell distribution of lymphatic tissue from the gastrointestinal tract of suckling piglets

Fatty acids are essential for immune cell function. Maternal dietary fatty acid supply influences body fat composition of their offspring. As a first step to study immunonutritional interactions at an early age of pigs, four sows were fed a diet containing sunflower oil or oil from seal blubber during pregnancy and lactation. Corresponding piglets were sacrificed at three consecutive time points in the suckling period and their mesenteric lymph nodes and spleen were analysed by gas chromatography for levels of fatty acid. At the same time mononuclear cells of these organs and of the intestinal lymphoid tissue from the jejunum were isolated and subpopulations characterised by flow cytometry. Levels of fatty acids from the lymphatic organs of the piglets were significantly influenced by the maternal diet. The concentration of the fatty acids 20:5n-3, 22:5n-3 and 22:6n-3 were higher in the spleen and mesenteric lymph node of piglets suckled to sows of the test diet. Additionally, suckling time affected the levels of some long chain polyunsaturated fatty acids. Dietary effects were seen on some subpopulations including CD4-CD8alpha+ lymphocytes of the mesenteric lymph nodes and CD4+CD8alpha+ lymphocytes of the lamina propria, which were higher in the group fed seal blubber oil. The levels of CD21+ B-cells were higher in the group fed sunflower oil. The results indicate that the maternal diet and suckling time affect the fatty acid status of the investigated lymphatic tissues of piglets, but may have minor effects on the investigated lymphocyte subpopulations.