Incorporation Of Linoleic Acid Research Articles

COMPARISON OF LINOLEIC AND CONJUGATED LINOLEIC ACIDS IN ENZYMATIC ACIDOLYSIS OF TRISTEARIN

ABSTRACTThe acyl incorporation and migration of linoleic and conjugated linoleic acids in enzymatic acidolysis were compared in a solvent‐free system. Two systems were used in the Lipozyme RM IM‐catalyzed acidolysis at 60C temperature and 5% by weight enzyme load (based on substrates). One included tristearin (SSS) and linoleic (L) or conjugated linoleic (cL) acids (1:6, mol/mol). The other was between tristearin and the mixture of linoleic and conjugated linoleic acids (1:3:3, mol/mol/mol). Acyl incorporation and migration together with triacylglycerol composition of the products were monitored with gas chromatography, pancreatic lipase hydrolysis, and high performance liquid chromatography. Both acyl incorporation and migration of linoleic acid were faster than those of conjugated linoleic acid. At 5 h reaction, there were 13.0% LLL, 46.5% LSL, 27.7% LSS, and 5.6% SSS in the product for a system between tristearin and linoleic acid; whereas there were 2.4% cLcLcL, 10.4% cLScL, 50.9% cLSS, and 36.2% SSS in the product for a system between tristearin and conjugated linoleic acid. The results suggest that linoleic acid was more reactive than conjugated linoleic acid in the enzymatic acidolysis probably because of the rigid structure of the latter.

Separation of glyceride positional isomers by silver ion chromatography

Separation of triglyceride and diglyceride positional isomers by silver ion high-performance liquid chromatography coupled with an evaporative light-scattering detector is described. The triglyceride isomers had a fatty acid composition of CLC and CCL, where C and L were caprylic acid and linoleic acid, respectively. Diglyceride isomers, 1,2(2,3)-diglyceride and 1,3-diglyceride, which contained caprylic acid were separated too. A solvent system based on n-hexane, 2-propanol, ethyl acetate, and acetonitrile with a flow-rate of 0.8 ml/min was developed. Calibration curves of CLC and CCL were achieved with triolein as internal standard. Using this method, the incorporation of linoleic acid onto specific a position of glycerol backbone can be monitored.

Defective Remodeling of Cardiolipin and Phosphatidylglycerol in Barth Syndrome

Cardiolipin (CL) and phosphatidylglycerol (PG) are the major polyglycerophospholipids observed in mammalian tissues. CL is exclusively found in the inner mitochondrial membrane and is required for optimal function of many of the respiratory and ATP-synthesizing enzymes. The role of CL in oxidative phosphorylation is, however, not fully understood and although reduced CL content leads to aberrant cell function, no human disorders with a primary defect in cardiolipin metabolism have been described. In this paper we present evidence that patients with the rare disorder X-linked cardioskeletal myopathy and neutropenia (Barth syndrome, MIM 302060) have a primary defect in CL and PG remodeling. We investigated phospholipid metabolism in cultured skin fibroblasts of patients and show that the biosynthesis rate of PG and CL is normal but that the CL pool size is 75% reduced, indicating accelerated degradation. Moreover, the incorporation of linoleic acid, which is the characteristic acyl side chain found in mammalian CL, into both PG and CL is significantly reduced, whereas the incorporation of other fatty acids into these phospholipids is normal. We show that this defect was only observed in Barth syndrome patients' cells and not in cells obtained from patients with primary defects in the respiratory chain, demonstrating that the observed defect is not secondary to respiratory chain dysfunction. These results imply that the G4.5 gene product, which is mutated in Barth syndrome patients, is specifically involved in the remodeling of PG and CL and for the first time identify an essential factor in this important cellular process.

Thioglycolate‐elicited rat macrophages exhibit alterations in incroporation and oxidation of fatty acids

Incorporation and oxidation of fatty acids (FA) were investigated in resident and thioglycolate-elicited (TG-elicited) rat macrophages (Mphi). Both cell types presented a time-dependent incorporation of [14C]-labeled palmitic acid (PA), oleic acid (OA), linoleic acid (LA), and arachidonic acid (AA) up to 6 h. The total amount of [14C]-FA incorporated by resident Mphi after 6 h was: AA > PA = LA > OA. TG-elicited cells presented a 50% reduction in the incorporation of LA, PA, and AA, whereas that of OA remained unchanged as compared to resident Mphi. The FA were oxidized by resident Mphi as follows: LA > OA > PA > AA. TG elicitation promoted a reduction of 42% in LA oxidation and a marked increase in AA oxidation (280%). The increased oxidation of AA in TG-elicited cells may account for the lower production of prostaglandins in Mphi under these conditions. The full significance of these findings for Mphi function, however, remains to be examined.

Enzymatic enrichment of conjugated linoleic acid isomers and incorporation into triglycerides

AbstractA method was developed for the enrichment of either the cis9,trans11 or the trans10,cis12 isomer of conjugated linoleic acid (CLA) from a synthetic CLA mixture consisting predominantly of these isomers in equal amounts. Lipases were screened for their ability to selectively esterify one isomer at a significantly greater rate than the other isomer. An immobilized lipase from Rhizomucor miehei was nonselective, but a lipase from Geotrichum candidum esterified the cis9,trans11 isomer more rapidly than the trans10,cis12 isomer. This selectivity was exploited at the kilogram scale to prepare an ester fraction with a content of 91% cis9,trans11 CLA and an unreacted free fatty acid fraction consisting of 82% trans10,cis12 CLA, based on total CLA content. The components of the reaction mixture were separated by molecular distillation. Each enriched fraction was then incorporated into palm oil triglycerides by interesterification with the non‐selective lipase from R. miehei. Two triglyceride fats resulted, which were enriched in either cis9,trans11 CLA (26.5% cis9,trans11 and 1.7% trans10,cis12) or trans10,cis12 CLA (3.5% cis9,trans11 and 22.9% trans10,cis12).

Lipid composition of hepatocyte plasma membranes from geese overfed with corn.

Twelve-week-old Landes male geese were overfed with corn for 21 d in order to induce liver steatosis (fatty liver). Lipid composition of hepatocyte plasma membranes from fatty livers was compared to that of lean livers obtained from geese fed a normal diet. The ratio cholesterol/phospholipids was higher in fatty hepatocyte plasma membranes (0.63 vs. 0.47), whereas the phospholipid/protein ratio was less than half. Overfeeding induced changes in fatty acid composition of hepatocyte plasma membranes, including a greater than twofold increase in the percentage of oleic acid (29.7 vs. 13.8%) and a somewhat lesser increase in lauric, palmitic, and palmitoleic acid contents of plasma membrane lipids of fatty livers. A concomitant reduction in the proportion of stearic acid (18.4 vs. 25.1%) was also observed. In fatty livers, the increased ratio of saturated to polyunsaturated fatty acids (PUFA) (1.5 vs. 1.0) was related to a significant decrease in PUFA content. Among all the PUFA, only the eicosatrienoic acid (20:3n-9) percentage was increased by liver steatosis. Overfeeding with corn appeared to induce competition between de novo synthesized and dietary fatty acids incorporated in hepatocyte plasma membranes. This resulted in an accumulation of de novo synthesized monounsaturated and derived fatty acids in plasma membranes from overfed birds. A defect in the incorporation of linoleic acid and linoleic- and linolenic-derived PUFA was observed despite the high proportion of these essential fatty acids in the diet. It was concluded that in overfed palmipeds, de novo hepatic lipogenesis prevails over dietary lipid intake to modulate lipid composition of the fatty liver plasma membrane.

Incorporation of linoleic acid by cultured human keratinocytes

Linoleic acid is required for the formation and maintenance of the epidermal barrier, but most of the current in vitro keratinocyte culture systems are linoleic acid-deficient. The aim of the present study was to examine the efficiency of linoleic acid uptake in human keratinocyte cultures grown under submerged and air-exposed conditions in serum-free medium. The water-insoluble linoleic acid was bound to carrier molecules (cyclodextrin or bovine serum albumin). Comparable results were obtained with home-made and commercially available linoleic acid complexes. In the submerged cultures, the increase of the linoleic acid medium concentration (ranging from 0 to 20 microg/ml) resulted in a gradual increase in the linoleic acid cellular content, which exceeded 1.4 times the value found in native epidermis when the highest concentration of linoleic acid was used. The addition of linoleic acid did not alter the profile of the other epidermal fatty acids, with the exception of oleic acid, which decreased in parallel with the increasing linoleic acid content. While the content of linoleic acid found in phospholipids was similar to that in native epidermis, a large excess of linoleic acid was detected in triglycerides, the synthesis of which was markedly increased in cultures grown submerged in medium containing higher concentrations of linoleic acid. Under air-exposed conditions, the dermal substrate used seemed to be the most limiting factor for efficient linoleic acid supplementation. A low linoleic acid cellular content was detected when an inert filter was used. De-epidermized dermis was found to be the most permeable substrate for linoleic acid complexes. The cellular linoleic acid content increased in a parallel with the increasing linoleic acid concentration (ranging from 4 to 30 microg/ml), but the overall amount incorporated was lower than that in submerged cultures. The content of linoleic acid in the phospholipid and ceramide fractions isolated from reconstructed epidermis grown under air-exposed conditions was close to that of native epidermis, but the triglycerides remained abnormally enriched in linoleic acid, indicating persistence of some anomalies in epidermal lipogenesis in vitro.

Chemically defined structured lipids: current status and future directions in gastrointestinal diseases.

Over the past two decades various concepts for the supply of lipids in parenteral and enteral nutrition have been developed. Traditionally, the nutritional dietary management typically includes physical mixtures of medium chain and long-chain triglycerides. Recently, chemically defined structured lipids have been developed that combine the advantages of conventional fats with those of special purposes. The first structured lipids were produced by mixing pure medium-chain triglycerides and long-chain triglycerides, allowing hydrolysis to free fatty acids, followed by random transesterification of the fatty acids into mixed triglyceride molecules. This results in a triglyceride containing combinations of short-, medium-, and long-chain fatty acids on a single glycerol backbone. These have unique chemical, physical, and/or physiological properties which differ from simply blending mixtures from the starting fats. By use of 1,3-specific or 2-specific lipases it is now possible to synthesize 1,3-specific or 2-specific triglycerides containing short- and/or medium-chain acids. For instance, incorporation of linoleic, arachidonic, or eicosapentaenoic acid at the sn-2 position is being evaluated for the specific objective of modulating membrane fatty acid composition and essential fatty acid absorption in models of cancer, burns, and immune dysfunction. This contribution reviews the current status of experimental and clinical studies of chemically defined structured lipid-based fat emulsions, with emphasis on their therapeutic potential for nutritional support in hospitalized patients.

Untersuchungen zum einfluss von palmfett und distelöl im futter von mastelterntierhennen auf befruchtung, schlupffähigkeit und wachstum der nachkommen

Das Ziel der Versuche bestand darin, den Einfluß einer gestaffelten Supplementierung von Palmfett oder Distelöl (25 g bzw. 50 g pro kg) ins Futter von Mastelterntierhennen auf Schlupfergebnis und Wachstum der Nachkommen zu prüfen. Die Fettsupplementierung führte zu veränderten Konzentrationen an Öl‐ und Linolsäure im Bruteidotter und war der Ausgangspunkt für vier Brutversuche (31 ./40./50./59. Lebenswoche der Zuchthennen) und Mastkükenaufzuchten (35 Tage). Die Anzahl an befruchteten Eiern (Versuch 1/2 ‐75%/88%) war zwischen beiden Versuchen gesichert unterschiedlich. Innerhalb der Versuche wurde dieses Merkmal sowohl vom Futter als auch Hennenalter verändert. Auf die embryonalen Verluste und die Anzahl an geschlüpften Küken (Versuch 1/2 ‐ 76%/78%) hatte das Dotterfettsäuremuster keinen Einfluß (P > 0,05). Während die Körpermasse der Küken (Versuch 1/2 : 43,3 g/43,7 g) gleich war, unterschied sich die Mastendmasse der Broiler (Versuch 1/2 : 1676 g/1764 g) zwischen den Versuchen gesichert. Die Unterschiede zwischen den Gruppen eines jeden Versuches ließen keine gesicherte Beziehung zu dem Zuchthennenfutter erkennen. Das Fettsäurenmuster der Triacylglyceride und Phospholipide des Restdottersackes der frischgeschlüpften Küken zeigte bei Öl‐ und Linolsäure die gleichen Abstufungen wie im Bruteidotter. Die Reduzierung des Gehaltes an Docosahexaensäure im Bruteidotter aufgrund einer steigenden Linolsäureeinlagerung, spiegelte sich in den Gehimphospholipiden der Küken (1./5. Tag) wider.

Effect of ganglioside GM1 on ethanol-induced changes in the incorporation of free fatty acids into membrane phospholipids in mouse brain.

Our previous studies with mice showed that chronic ethanol (EtOH) administration affected the incorporation of unsaturated free fatty acids (FFA) into four major brain phospholipids (PL). In the current study, we investigated the effects of ganglioside GM1 pretreatment on EtOH-induced changes in the incorporation of various FFA into cerebral PL in mice. Consistent with our earlier findings, the results suggest that chronic EtOH exposure alters the incorporation of unsaturated fatty acids into phosphatidylinositol (PI), phosphatidylserine, and phosphatidylcholine (PC), but not into phosphatidylethanolamine (PE). No significant differences were observed with stearic acid. The ganglioside GM1 treatment led to increased incorporation of linoleic acid (LA) into PE and PC and appeared to enhance the EtOH-produced effects especially for docosahexaenoic acid (DHA) and to a lesser extent for oleic acid, LA, and arachidonic acid, when compared to the untreated control group. However, when comparison was made with the EtOH-alone group, significant differences were observed only with DHA incorporation and mainly into PE and PI. Thus acyltransferases may play an important role in membrane adaptation to the injurious effects of EtOH and GM1 appears to enhance selective incorporation of FFA into membrane PL; a process that may represent a repair mechanism.

The Influence of Kynurenine and Its Metabolites on Lipid Metabolism

Summary Incorporation of fatty acids into phospholipids has been investigated using samples of rat liver tissue homogenate, Krebs-Ringer-phosphate buffer (pH=7.4) containing 0.3% albumin, fatty acid mixture and glycerol. The addition of L-kynurenine (4 nmoljg wet weight) to incubation medium induced an increase of palmitic, oleic and linolenic acid and decrease of linoleic and arachidonic acid incorporation into phospholipids. These changes of fatty acid incorporation into phospholipids were followed by increase of cholesterol and decrease of phospholipids content in samples. The addition of 3-hydroxykynurenine (1.8 and 4 nmoljg wet weight), 3-hydroxyanthranilic acid (2.2 and 4 nmoljg wet weight) ,1n..:l quinolinic acid (2.4 and 4 nmoljg wet weight) to incubation medium for phospholipid biosynthesis ill vitro induced a decrease of stearic, palrnitic and linoleic acid and an increase of oleic and especially arachidonic acid incorporation into phospholipids. These changes were accompanied by a decrease of cholesterol content in samples. The influence of kynurenine on fatty acid incorporation into phospholipids was similar to that of neopterin observed earlier. The other tryptophan degradation products behaved similar to the reduced pteridine derivatives. Our results allow to suggest that L-kynurenine decreases, while 3-hydroxykynurenine, 3-hydroxyanthranilic acid and quinolinic acid increase membrane fluidity in the studied concentrations.

Effect of growth temperature on the biosynthesis of eukaryotic lipid molecular species by the cyanobacterium Spirulina platensis

The incorporation of linoleic acid added at mmolar concentrations to the culture medium of the photosynthetic prokaryote Spirulina platensis results in the synthesis of membrane glycerolipids with a eukaryotic distribution of fatty acid chain length on the glycerol backbone (Pham Quoc et al., Biochim. Biophys. Acta [1993] 1168, 94–99). This distribution contrasts with the usual prokaryotic one found in lipids of cyanobacteria. A subsequent desaturation of the exogenously supplied fatty acid resulted in a large increase of γ-linolenic acid. In order to estimate the capacities of S. platensis for bioconversion of fatty acids in lipid classes, the effects of different temperatures of growth were studied in linoleic acid-supplemented cultures. The lipid composition was affected by growth temperature, the synthesis of SQDG was stimulated at low temperature. The molecular species of each lipid were isolated and analyzed. Whatever the temperature of growth, the biosynthesis of eukaryotic C18/C18 lipid molecular species was observed in all lipid classes. Furthermore, the proportion of eukaryotic lipids increased at low temperature (24°C). The desaturation of C18 fatty acids at C1 and C2 positions of the glycerol moiety occurred and was further stimulated when the growth temperature was lowered. The resulting proportion of γ-linolenic acid increased significantly in cultures supplemented with linoleate at low temperatures. Finally a pathway for the synthesis of eukaryotic lipids and the desaturation of fatty acids esterified to the acyl lipids of linoleate-supplemented S. platensis can be suggested.

Kynurenine and pteridines in changes of membrane fluidity.

Examination of blood serum lipid and kynurenine content in patients with ischemic heart disease and patients with essential hypertension showed that the elevated whole cholesterol and decreased HDL-cholesterol content were not dependent on kynurenine accumulation in blood. The difference was found out in triglycerol and phospholipid amount. Kynurenine accumulation was followed by an increase of triglycerol and a decrease of phospholipid, especially lecitin amount as well as an increased saturated and decreased unsaturated fatty acid content of phospholipids (Rudzite et al.,1988, 1994). The same changes of lipids were also found in white rats with experimentally induced kynurenine accumulation in blood serum (Rudzite and Jurika, 1991). Moreover, kynurenine addition to incubation medium for phospholipid biosynthesis in vitro was followed by an increase of palmitic and oleic acid, a decrease of linoleic and arachidonic acid incorporation into phospholipids. Further studies showed, that similar deviation in fatty acid incorporation into phospholipids was seen after neopterin addition to incubation medium for phospholipid biosynthesis in vitro. The difference was only in oleic acid incorporation:neopterin decreased, while L-kynurenine increased the oleic acid incorporation into phospholipids (Rudzite et al., 1993,1994).

Use of human pseudo-epidermis to evaluate the toxicity of bis-(2-chloroethyl)sulfide (BCES) on water permeation barrier formation and function

Human pseudo-epidermis was used to investigate the effects of bis-(2-chloroethyl)sulfide (BCES) on the formation and function of the water permeation barrier. To generate the culture, 2 million viable basal cells derived from human skin were plated on a Puropore nylon microporous membrane pre-coated with calf skin collagen. Addition of bovine pituitary extract and epidermal growth factor to the medium favored the formation of homogeneous cultures and better barrier function. The water permeation constant ( K p) was shown to decrease significantly and reached 25 ± 6 × 10 −3 when it was calculated from 71% of the cultures prepared. The effects of topically applied BCES on the incorporation of [ 14C]linoleic acid, as a marker for lipid synthesis, and K p, as a measure of water permeation, were studied. Compared with untreated cultures, there was no difference in the K p immediately after exposure to 1–10 nmol BCES/cm 2 for 30 min. On the other hand, [ 14C]linoleic acid incorporation was dose-dependently decreased immediately after exposure and then returned to normal by 48 h later. These data suggest that BCES produces no direct damage to the water permeation barrier but may affect barrier formation by inhibiting lipid synthesis.

Triacylglycerol metabolism by lymphocytes and the effect of triacylglycerols on lymphocyte proliferation.

This study investigates the ability of lymphocytes to utilize fatty acids originating from triacylglycerols and the effect of triacylglycerols upon mitogen-stimulated lymphocyte proliferation. Lymphocytes isolated from rat lymph nodes, spleen, thymus and lymphatic duct had a lipoprotein lipase activity of approx. 10 units/mg of protein, indicating that the fatty acids of circulating triacylglycerols are accessible to these cells. In culture lymph node lymphocytes hydrolysed triacylglycerols added to the medium as emulsions. Both non-esterified fatty acids and free glycerol appeared in the cell culture medium, but their concentrations indicated that a high proportion of each (65-90% of fatty acids and 60-80% of glycerol) was taken up by the cells. The incorporation and fate of triacylglycerol-fatty acids was studied by culturing the cells in the presence of tri[3H]oleoylglycerol or tri[14C]inoleoylglycerol. Both fatty acids were incorporated into lymphocyte lipids in a time-dependent manner; linoleic acid was incorporated at a significantly greater rate than oleic acid. The majority of oleic acid (greater than 70%) was incorporated into cellular triacylglycerol, while less than 10% was incorporated into phospholipids. In contrast, linoleic acid incorporation into cellular triacylglycerol never exceeded 25%, while up to 45% was incorporated into phospholipids. Triacylglycerols containing polyunsaturated fatty acids inhibited concanavalin A-stimulated lymphocyte proliferation in a concentration- and time-dependent manner; triacylglycerols containing saturated fatty acids or oleic acid were not inhibitory. Such direct effects of certain triacylglycerols on lymphocyte function may explain why some clinical trials of polyunsaturated fatty acid-rich diets have been successful in improving the condition of patients suffering from inflammatory diseases.

Effect of Sesamin on Cholesterol Synthesis and on the Distribution of Incorporated Linoleic Acid in Lipid Subfractions in Cultured Rat Cells

Since sesamin influences the metabolism of essential fatty acids, its effects on cholesterol metabolism and on the incorporation of linoleic acid were studied by using cultured rat artery smooth muscle cells (SMCs) and primary cultured rat hepatocytes. Cholesterol synthesis from acetate was inhibited by sesamin in SMCs, and the distribution of incorporated linoleic acid in the lipid and phospholipid subfractions was altered by sesamin in rat hepatocytes.

Formation of prostanoids and hydroxy fatty acids by stimulated peritoneal mast cells: Role of the dietary fat type in rat

To study the influence of membrane fatty acid composition on the formation of prostanoids and hydroxy fatty acids by rat peritoneal mast cells (MC), animals were fed three different types of fatty acids: mackerel oil (MO), abundant in n−3 fatty acids; sunflower seed oil (SO), rich in linoleic acid; and hydrogenated coconut oil (HCO), mainly containing saturated fatty acids. The presence of n−3 fatty acids in the diet resulted in the incorporation of 20:5( n− 3), 22:5( n−3) and 22:6( n − 3) in MC phospholipids. A decrease of arachidonic acid, 20:4( n−6), was observed in MC-phospholipids of the MO-fed animals. Furthermore, increasing the relative amounts of 18:2( n−6) in the diet (SO group) led to an increased incorporation of linoleic acid, 18:2( n−6) in MC phospholipids when compared to both other dietary groups. The changes in MC phospholipid fatty acid composition were (partly) reflected in the formation of prostanoids and hydroxy fatty acids upon stimulation with the calcium ionophore A23187. The decrease in arachidonic acid content in MC phospholipids of MO-fed rats resulted in a decreased formation of PGD 2 when compared to both other groups. Also, the increased amounts of 18:2( n−6) in MC phospholipids of SO-fed rats resulted in an increased formation of 9-and 13-HODE upon stimulation. The results show that modifications in the fatty acid composition of the diet influences MC membrane fatty acid composition which ultimately results in changes in prostanoid and hydroxy fatty acid synthesis by MC upon stimulation with the calcium ionophore A23187.

Chemical and alpha-chymotrypsin-mediated proteolytic degradation of insulin in bile salt-unsaturated fatty acid mixed micellar systems.

The proteolytic degradation of porcine zinc insulin by alpha-chymotrypsin was previously found to depend markedly on the state of insulin aggregation (Pharm. Res. 9:864-869, 1992). In this study, the effect of bile salt-unsaturated fatty acid mixed micelles on alpha-chymotryptic degradation of insulin was further characterized. The incorporation of linoleic acid has greatly accelerated insulin degradation with the apparent first order rate constant being linearly related to the concentration of linoleic acid. At a 10 mM linoleic acid concentration solubilized in 10 mM sodium glycocholate, the proteolytic degradation rate constant increased by 16 times, which could not be explained solely by the mechanism of insulin oligomer dissociation. Further, this effect is significantly reduced when the free carboxylic group of linoleic acid is methylated. The catalytic role of mixed micelles on chemical degradation of insulin was found to depend on the concentration of linoleic acid incorporated. When solubilized in the form of mixed micelles, linoleic acid chemically catalyzes peptide bond cleavage in a concentration-dependent manner.

Inhibition of vasopressin-induced formation of diradylglycerols in vascular smooth muscle cells by incorporation of eicosapentaenoic acid in membrane phospholipids.

Eicosapentaenoic acid and linoleic acid exert antihypertensive effects by an unknown mechanism unrelated to prostanoids, a property which is not shared by arachidonic acid. This study investigated the influence of these three acids on the formation of diradylglycerols and phosphatidic acid, key intracellular messengers involved in the mediation of agonist-induced vascular smooth muscle cell contraction. Rat mesenteric artery vascular smooth muscle cells in culture were pre-incubated for 24 h with eicosapentaenoic acid, linoleic acid or arachidonic acid. After thorough washing the cells were then incubated for 20 min in the presence of arginine vasopressin or vehicle, either immediately or following cell labelling with 32P-orthophosphate. The fatty acid composition of cell lipids was determined by gas chromatography after transesterification in the presence of boron trifluoride and methanol. Diradylglycerols and 32P-phosphatidic acid were purified from cell lipid extracts by thin-layer chromatography and diradylglycerols were analysed. Incubation of vascular smooth muscle cells with eicosapentaenoic acid, linoleic acid or arachidonic acid resulted in the incorporation of these fatty acids at the sn-2 position of membrane phospholipids, mainly phosphatidylcholine and phosphatidylethanolamine. Eicosapentaenoic acid treatment was associated with a reduction, and linoleic acid treatment with an increase in the relative proportions of arachidonic acid found in cell phospholipids. Arginine vasopressin stimulated the formation of both diradylglycerols and 32P-phosphatidic acid. The arginine vasopressin-induced stimulation of diradylglycerols accumulation was almost completely abolished in eicosapentaenoic acid-treated cells, whereas it was not modified by linoleic acid or by arachidonic acid treatment. The arginine vasopressin-stimulated formation of 32P-phosphatidic acid was significantly inhibited by linoleic acid treatment but was not influenced by eicosapentaenoic acid or arachidonic acid treatment. The incorporation of eicosapentaenoic acid or linoleic acid at the sn-2 position of membrane phospholipids leads to an inhibition of arginine vasopressin-induced formation of diradylglycerols or phosphatidic acid, respectively, in rat mesenteric artery vascular smooth muscle cells in culture. These properties may contribute to the antihypertensive effects in these fatty acids in vitro.

Effects of increasing dietary linoleic acid on phospholipid fatty acid composition and eicosanoid production in leucocytes and gill cells of Atlantic salmon ( Salmo salar)

Diets containing linoleic acid at 10, 25 and 45% of total dietary fatty acids were fed to three groups of post-smolt Atlantic salmon ( Salmo salar) for 18 weeks. Incorporation of linoleic acid into membrane phospholipids of leucocytes and gills increased in response to dietary intake. In general, there was an increase in arachidonic acid and a decrease in eicosapentaenoic acid in the individual phospholipids of both cell types in response to increasing dietary linoleic acid. These changes in eicosanoid precursors were reflected in significantly increased plasma concentrations of 6-keto-PGF 1α and TXB 2 in salmon given the highest dietary linoleic acid. In whole blood stimulated with the calcium ionophore A23187, LTB 4, 12-HETE and TXB 2 were significantly increased and 12-HEPE significantly decreased in response to increasing dietary linoleic acid. In isolated gill cells stimulated with A23187, 12-HEPE, 12-HETE, 14-HDHE and TXB 2 were all decreased in response to increasing dietary linoleic acid, although the ratio of 12-HEPE/12-HETE was also decreased.