Fatty acids specifically related to the anisotropic properties of plasma membrane from rat urothelium

Four different luminal surfaces of rat urothelium differing in their fatty acid composition were prepared by dietary induction. In order to induce lipid changes, each of four groups of rat received a basal diet rich in one of the unsaturated n-3, n-6 or n-9 fatty acid families and a commercial (control) diet. The effects of the dietary regime on the fatty acid composition of luminal urothelial membranes and their relation to the mobility of fluorescent probes were studied. In comparison with the control diet membrane, all three fatty acid-rich diets induced a decrease of the percentage amount of saturated fatty acid while that of the unsaturated fatty acids was increased. Accordingly, all three diets increased the unsaturation index in comparison with the control diet. The anisotropy across each membrane fraction was assessed using the n-(9-anthroyloxy) fatty acid fluorescent probes 3-AS, 7-AS and 12-AS, which locate at different depths in the membrane. Two different anisotropy profiles were observed. One profile showed the highest anisotropy at the C7 depth, whereas the other exhibited a continuous decrease of the anisotropy from the surface to the center of the bilayer. The molecular properties (isomerization) of 18:2n-9 fatty acid may account, at least in part, for the observed V-shaped profile (the ascending trend) of the membrane anisotropy values as a function of the respective 18:2n-9 fatty acid contents. Nevertheless, the minimum value of the profile did not correspond to the minimum 18:2n-9 fatty acid content, but rather to the higher amount of docosahexaenoic (22:6n-3) fatty acid. Thus, a modulating role of the 22:6n-3 fatty acid on the rigidifying effect of 18:2n-9 fatty acid is suggested, possibly mediated by relationships between fatty acid composition, saturated and unsaturated chain lengths, and freedom of motion of the phospholipid acyl chains.     

Phosphatidylethanolamine methyltransferase: evidence for influence of diet fat on selectivity of substrate for methylation in rat brain synaptic plasma membranes

Male weanling rats were fed diets containing 20% (w/w) fat differing in fatty acid composition for 24 days. Synaptic plasma membranes were isolated from the brain and the fatty acid composition of phosphatidylethanolamine and phosphatidylcholine was determined. In vitro assays of phosphatidylethanolamine methyl-transferase activity were performed on fresh membrane samples to assess effect of dietary fat on the rate of phosphatidylethanolamine methylation for phosphatidylcholine synthesis via the phosphatidylethanolamine methyltransferase pathway. Dietary level of n-6 and ratio of n-6 to n-3 fatty acids influenced membrane phospholipid fatty acid composition and activity of the lipid-dependent phosphatidylethanolamine methyltransferase pathway. Rats fed a diet rich in n-6 fatty acids produced a high ratio of n-6/n-3 fatty acids in synaptosomal membrane phosphatidylethanolamine, and elevated rates of methylation of phosphatidylethanolamine to phosphatidylcholine by phosphatidylethanolamine methyltransferases, suggesting that the pathway exhibits substrate selectivity for individual species of phosphatidylethanolamine containing long-chain homologues of dietary n-6 and n-3 fatty acids (20:4(n-6), 22:4(n-6), 22:5(n-6) and 22:6(n-3). It may be concluded that diet alters the membrane content of n-6, n-3 and monounsaturated fatty acids, and that change in phosphatidylethanolamine species available for methylation to phosphatidylcholine alters the rate of product synthesis in vivo by the phosphatidylethanolamine methyltransferase pathway.     

Response of rat heart membranes and associated ion-transporting ATPases to dietary lipid

The effects of different dietary fat intake on the lipid composition and enzyme behaviour of sarcolemmal (Na+ + K+)ATPase and sarcoplasmic reticulum Ca2+-ATPase from rat heart were investigated. Rat diets were supplemented with either sunflower seed oil (unsatd./satd. 5.6) or sheep kidney fat (unsatd./satd. 0.8). Significant changes in the phospholipid fatty acid composition were observed in both membranes after 9 weeks dietary lipid treatment. For both membranes, the total saturated/unsaturated fatty acid levels were unaffected by the dietary lipid treatment, however the proportions of the major unsaturated fatty acids were altered. Animals fed the sunflower seed oil diet exhibited an increase in n-6 fatty acids, including linoleic (18:2(n-6] and arachidonic (20:4(n-6] while the sheep kidney fat dietary rats were higher in n-3 fatty acids, principally docosahexaenoic (22:6), with the net result being a higher n-6/n-3 ratio in the sunflower seed oil group compared to sheep kidney fat dietary animals. Fluorescence polarization indicated that the fluidity of sarcoplasmic reticular membrane was greater than that of sarcolemmal membrane, with a dietary lipid-induced decrease in fluidity being observed in the sarcoplasmic reticular membrane from sheep kidney fat dietary animals. Despite these significant changes in membrane composition and physical properties, neither the specific activity nor the temperature-activity relationship (Arrhenius profile) of the associated ATPases were altered. These results suggest that with regard to the parameters measured in this study, the two ion-transporting ATPases are not modulated by changes which occur in the membrane lipid composition as a result of the diet.     

Altered Composition of Cerebral Microvessel Membrane Phosphoglycerides from Senescent Mouse

Abstract— Phosphoglyceride and fatty acid composition was determined in the cellular membranes of isolated cerebral microvessels and brain parenchymal cells (neurons and glia) taken from 10-, 20-, and 27–30-month-old C57BL6/NNIA mice. Lipids were extracted from each fraction and the fatty acid profiles of ethanolamine, cho-line, serine, and inositol phosphoglycerides analyzed by gas chromatography. The results suggest that membrane phosphoglycerides from cerebral microvessels are significantly more affected by the aging process than are those of the brain parenchyma. Relative percentage for fatty acids in cerebral microvessels indicate an overall decline in membrane unsaturation with a concomitant elevation in the level of saturation. The decline in unsaturation is reflected primarily in the loss of precursor fatty acids for arachidonic (18:2n-6 and 20:3n-6) and docosahexaenoic (20:5n-3 and 22:5n-3) acids. Levels of arachidonic (20:4n-6) and docosahexaenoic (22:6n-3) acids in each phos-phoglyceride remained unchanged with age; however, mol% for ethanolamine plasmalogen, a major source of these fatty acids, was significantly reduced in 27–30-month-old mice. Conversely, mol% for choline phospho-glyceride increased with age. The age-related changes in fatty acid profile for microvessel membrane phosphoglycerides are reflected by increased saturation/unsaturation ratios and decreased unsaturation indices. These parameters were not affected by aging in parenchymal membranes.     

EFFECTS OF DIFFERENT DIETARY LEVELS OF ESSENTIAL FATTY ACIDS ON THE FATTY ACID COMPOSITION OF ETHANOLAMINE PHOSPHOGLYCERIDES IN MYELIN AND SYNAPTOSOMAL PLASMA MEMBRANES

Abstract— Three dietary levels of essential fatty acids (EFA), 3 0, 0 75 and 0 07 calorie-% were fed to rats for two generations or more. Myelin was isolated at the ages of 18, 30, 45 and 120 days and synaptosomal plasma membranes at 18, 30 and 45 days. No difference was found in the lipid composition between the dietary groups in either subcellular fraction. The fatty acid patterns of ethanolamine phosphoglycerides (EPG) were analysed. In myelin the proportions of 18:1 and 20:1 increased with age, while those of 20:4 (n-6) and 22:6 (n-3) decreased, in synaptosomal plasma membranes the proportions of 20:4 (n-6) decreased with age, but 22:6 (n-3) increased and the sum of the polyunsaturated fatty acids was constant. At no age were significant differences found between the proportions of saturated and monounsaturated fatty acids, in either myelin or the synaptosomal plasma membrane fraction, when the different dietary groups were compared. In myelin from rats fed 007 calorie-% EFA the proportions of 20:4 (n-6) were slightly lower than in the two other groups, while those of 22 6 (n-3) were considerably lower. The synaptosomal plasma membranes fraction of rats fed O-07 calorie-% EFA had equal or slightly larger amounts of 20:4 (n-6) than in the two other groups, while 22:6 (n-3) was considerably smaller. In both subcellular fractions the decreased proportion of fatty acids of linoleic and linolenic acid series was compensated for by an increase in 20:3 (n-9) and 22:3 (n-9). The sum of these two fatty acids was equal in the EPG of myelin and synaptosomal plasma membranes at 18 days of age. At 30 and 45 days of age a lower value was found in the synaptosomal plasma membranes, while in the myelin fraction a slight decrease was found only at 120 days of age.     

Effect of In Vivo Modulation of Membrane Docosahexaenoic Acid Levels on the Dopamine-Dependent Adenylate Cyclase Activity in the Rat Retina

Abstract: We have studied the effect of a dietary deprivation of n-3 fatty acids on the activity of the dopamine (DA)-de-pendent adenylate cyclase in the rat retina. Experiments were conducted in 6-month-old rats raised on semipurified diets containing either safflower oil (n-3 deficient diet) or soybean oil (control diet). The levels of docosahexaenoic acid [22:6 (n-3)] in retinal phospholipids were significantly decreased in n-3 deficient rats (35–42% of control levels). This was compensated by a rise in 22:5 (n-6), the total content of poly-unsaturated fatty acids (PUFA) remaining approximately constant. Adenylate cyclase activity was measured in retinal membrane preparations from dark-adapted or light-exposed rats. The enzyme activity was stimulated by DA and SKF 38393 in a light-dependent fashion. The activation was lower in rats exposed to light than in dark-adapted animals, suggesting a down-regulation of the DI DA receptors by light. The activation by guanine nucleotides and forskolin was also decreased in light-exposed rats. There was no significant effect of the dietary regimen on the various adenylate cyclase activities and their response to light. Furthermore, the guanine nucleotide- and DA-dependent adenylate cyclase activities of retinal membranes were found to be relatively resistant to changes in membrane fluidity induced in vitro by benzyl alcohol. The results indicate that in the absence of changes in total PUFA content, a decreased ratio of n-3 to n-6 fatty acids in membrane phospholipids does not significantly affect the properties of adenylate cyclase in the rat retina.     

Dietary supplementation of N-3 fatty acids and hydroperoxide levels in rat retinas.

Docosahexaenoic acid (DHA) plays an important role in visual and neural development in mammals. In the present study, effect of dietary supplementation with n-3 fatty acids, primarily docosahexaenoic acid (DHA) with high purity, on the fatty acid composition of photoreceptor cells of young rats (fed from 4 weeks) was investigated. DHA in rod outer segment (ROS) membranes was significantly increased in the group of high DHA feeding (9.69% total energy). Other n-3 fatty acids (alpha-linolenic acid (ALA) and eicosapentaenoic acid (EPA)) included in the diets with DHA (0.95%-5.63% total energy) also significantly increased the proportion of DHA compared with the linoleic acid diet groups. However, the proportions of arachidonic acid (ARA) and other long chain n-6 fatty acids (22:4n6 and 22:5n6) were suppressed in these n-3 fatty acids-fed groups. Phospholipid hydroperoxides in ROS membranes were determined using a highly sensitive analytical technique, chemiluminescence-high performance liquid chromatography (CL-HPLC). There was no increasing tendency in the hydroperoxide levels of ROS membranes containing high content of DHA, and phosphatidylethanolamine hydroperoxide (PEOOH) was much lower than phosphatidylcholine hydroperoxide (PCOOH) under normal light conditions, which implies that DHA supplementation does not much affect the peroxidizability of ROS membranes in vivo. But UV irradiation on separated ROS membranes accelerated the formation of phospholipid hydroperoxides in high DHA feeding rats, and PEOOH was produced more efficiently than PCOOH in vitro.     

Dietary supplementation of N-3 fatty acids and hydroperoxide levels in rat retinas

Docosahexaenoic acid (DHA) plays an important role in visual and neural development in mammals. In the present study, effect of dietary supplementation with n-3 fatty acids, primarily docosahexaenoic acid (DHA) with high purity, on the fatty acid composition of photoreceptor cells of young rats (fed from 4 weeks) was investigated. DHA in rod outer segment (ROS) membranes was significantly increased in the group of high DHA feeding (9.69% total energy). Other n-3 fatty acids (α-linolenic acid (ALA) and eicosapentaenoic acid (EPA)) included in the diets with DHA (0.95%～5.63% total energy) also significantly increased the proportion of DHA compared with the linoleic acid diet groups. However, the proportions of arachidonic acid (ARA) and other long chain n-6 fatty acids (22:4n6 and 22:5n6) were suppressed in these n-3 fatty acids-fed groups. Phospholipid hydroperoxides in ROS membranes were determined using a highly sensitive analytical technique, chemiluminescence-high performance liquid chromatography (CL-HPLC). There was no increasing tendency in the hydroperoxide levels of ROS membranes containing high content of DHA, and phosphatidylethanolamine hydroperoxide (PEOOH) was much lower than phosphatidylcholine hydroperoxide (PCOOH) under normal light conditions, which implies that DHA supplementation does not much affect the peroxidizability of ROS membranes in vivo. But UV irradiation on separated ROS membranes accelerated the formation of phospholipid hydroperoxides in high DHA feeding rats, and PEOOH was produced more efficiently than PCOOH in vitro.     

Conservation of Docosahexaenoic Acid in Rod Outer Segments of Rat Retina During n-3 and n-6 Fatty Acid Deficiency

We investigated the mechanism by which rat retina conserves docosahexaenoic acid during essential fatty acid deficiency. Weanling female albino rats were fed diets containing either 10% by weight hydrogenated coconut oil, safflower oil, or linseed oil for 15 weeks. Plasma and rod outer segment (ROS) membranes were prepared for fatty acid and phospholipid molecular species analysis. In addition, retinas were removed for morphometric analysis. We found the following: (1) Plasma phospholipids and cholesterol esters from coconut oil, safflower oil, and linseed oil diet groups were enriched in 20:3(n-9), 20:4(n-6), and 20:5(n-3), respectively. The levels of these 20-carbon fatty acids in the ROS, however, were only slightly affected by diet. (2) The fatty acids and molecular species of ROS phospholipids from the safflower oil and coconut oil groups showed a selective replacement of 22:6(n-3) with 22:5(n-6), as evidenced by a reduction of the 22:6(n-3)-22:6(n-3) molecular species and an increase in the 22:5(n-6)-22:6(n-3) species. (3) The renewal rate of ROS integral proteins, determined by autoradiography, was 10% per day for each diet group. (4) Morphometric analysis of retinas showed no differences in the outer nuclear layer area or in ROS length between the three groups. We conclude that the conservation of 22:6(n-3) in ROS is not accomplished through reductions in the rate of membrane turnover, the total amount of ROS membranes, or in the number of rod cells. The retina may conserve 22:6(n-3) through recycling within the retina or between the retina and the pigment epithelium, or through the selective uptake of 22-carbon polyunsaturated fatty acids from the circulation.     

Alteration in Fatty Acid Composition of Adult Rat Brain Capillaries and Choroid Plexus Induced by a Diet Deficient in n-3 Fatty Acids: Slow Recovery After Substitution with a Nondeficient Diet

Wistar rats were fed for three generations with a semisynthetic diet containing either 1.5% sunflower oil (940 mg% of C18:2n-6, 6 mg% of C18:3n-3) or 1.9% soya oil (940 mg% of C18:2n-6, 130 mg% of C18:3n-3). At 60 days of age, the male offspring of the third generation were killed. The fatty acyl composition of isolated capillaries and choroid plexus was determined. The major changes noted in the fatty acid profile of isolated capillaries were a reduction (threefold) in the level of docosahexaenoic acid and, consequently, a fourfold increase in docosapentaenoic acid in sunflower oil-fed animals. The total percentage of polyunsaturated fatty acids was close to that in the soya oil-fed rats, but the ratio of n-3/n-6 fatty acids was reduced by threefold. In the choroid plexus, the C22:6n-3 content was also reduced, but by 2.6-fold, whereas the C22:5n-6 content was increased by 2.3-fold and the ratio of n-3/n-6 fatty acids was reduced by 2.4-fold. When the diet of sunflower oil-fed rats was replaced with a diet containing soya oil at 60 days of age, the recovery in content of n-6 and n-3 fatty acids started immediately after diet substitution; it progressed slowly to reach normal values after 2 months for C22:6n-5 and 2.5 months for C22:6n-3. The recovery in altered fatty acids of choroid plexus was also immediate and very fast. Recovery in content of C22:5n-6 and C22:6n-3 was complete by 46 days after diet substitution.     

Fatty acid composition of membrane bilayers: Importance of diet polyunsaturated fat balance

In one of the most extensive analyses to date we show that the balance of diet n-3 and n-6 polyunsaturated fatty acids (PUFA) is the most important determinant of membrane composition in the rat under 'normal' conditions. Young adult male Sprague-Dawley rats were fed one of twelve moderate-fat diets (25% of total energy) for 8weeks. Diets differed only in fatty acid (FA) profiles, with saturate (SFA) content ranging 8-88% of total FAs, monounsaturate (MUFA) 6-65%, total PUFA 4-81%, n-6 PUFA 3-70% and n-3 PUFA 1-70%. Diet PUFA included only essential FAs 18:2n-6 and 18:3n-3. Balance between n-3 and n-6 PUFA is defined as the PUFA balance (n-3 PUFA as % of total PUFA) and ranged 1-86% in the diets. FA composition was measured for brain, heart, liver, skeletal muscle, erythrocytes and plasma phospholipids, as well as adipose tissue and plasma triglycerides. The conformer-regulator model was used (slope=1 indicates membrane composition completely conforming to diet). Extensive changes in diet SFA, MUFA and PUFA had minimal effect on membranes (average slopes 0.01, 0.07, 0.07 respectively), but considerable influence on adipose tissue and plasma triglycerides (average slopes 0.27, 0.53, 0.47 respectively). Diet balance between n-3 and n-6 PUFA had a biphasic influence on membrane composition. When n-3 PUFA<10% of total PUFA, membrane composition completely conformed to diet (average slope 0.95), while diet PUFA balance>10% had little influence (average slope 0.19). The modern human diet has an average PUFA balance ~10% and this will likely have significant health implications.     

Reduced G protein-coupled signaling efficiency in retinal rod outer segments in response to n-3 fatty acid deficiency

The fatty acid (FA) docosahexaenoic acid (DHA, 22: 6n-3) is highly enriched in membrane phospholipids of the central nervous system and retina. Loss of DHA because of n-3 FA deficiency leads to suboptimal function in learning, memory, olfactory-based discrimination, spatial learning, and visual acuity. G protein-coupled receptor (GPCR) signal transduction is a common signaling motif in these neuronal pathways. Here we investigated the effect of n-3 FA deficiency on GPCR signaling in retinal rod outer segment (ROS) membranes isolated from rats raised on n-3-adequate or -deficient diets. ROS membranes of second generation n-3 FA-deficient rats had approximately 80% less DHA than n-3-adequate rats. DHA was replaced by docosapentaenoic acid (22:5n-6), an n-6 FA. This replacement correlated with desensitization of visual signaling in n-3 FA-deficient ROS, as evidenced by reduced rhodopsin activation, rhodopsin-transducin (G(t)) coupling, cGMP phosphodiesterase activity, and slower formation of metarhodopsin II (MII) and the MII-G(t) complex relative to n-3 FA-adequate ROS. ROS membranes from n-3 FA-deficient rats exhibited a higher degree of phospholipid acyl chain order relative to n-3 FA-adequate rats. These findings reported here provide an explanation for the reduced amplitude and delayed response of the electroretinogram a-wave observed in n-3 FA deficiency in rodents and nonhuman primates. Because members of the GPCR family are widespread in signaling pathways in the nervous system, the effect of reduced GPCR signaling due to the loss of membrane DHA may serve as an explanation for the suboptimal neural signaling observed in n-3 FA deficiency.     

Effect of an essential fatty acid deficiency on the phospholipid composition in anterior pituitary membranes.

The effects of an essential fatty acid deficient diet were investigated on the phospholipid fatty acids of several membrane fractions of the rat anterior pituitary, the secretion of which is known to be partly dependent on the membrane phospholipidic constituents. In standard dietary conditions, arachidonic acid (20:4n-6) and its elongation product, adrenic acid (22:4n-6), were the two main polyunsaturated fatty acids in all fractions studied. In rats deprived of EFA for 6 weeks after weaning, the levels of both 20:4n-6 and 22:4n-6 were not changed in microsomal + plasma membrane and nuclear fractions, whereas they were decreased in heavy mitochondrial and light mitochondrial fractions. The present data suggest a mechanism of compensation between membrane fractions which may preferentially preserve 20:4n-6 and 22:4n-6 in discrete membrane fractions.     

Lipid diet and enterocyte microsomal membrane fluidity in rats

Rats were fed on diets more or less enriched with n-3 and n-6 unsaturated fatty acids, before removal of the small intestine. The global protein, cholesterol and phospholipid contents of enterocyte microsomes were measured. Fatty acids of the total lipid extracts were determined. Acyl coenzyme A: cholesterol acyl transferase (ACAT) was chosen as the enzyme whose activity reflects metabolic changes induced by lipid diets. Fluorescence measurements using diphenylhexatriene as the membrane probe were performed. As dietary fat may change the fatty acid composition of membranes, the order parameter S calculated from fluorescence measurements was studied with regard to dietary fatty acid composition. The S values, distributed over a large range, were not different between rat groups. They were positively correlated with the ratios of cholesterol and proteins to phospholipids and the molar percentage of saturated fatty acids. ACAT activity was negatively correlated with S. Variations in S values among rats, whatever the diet, could in part be attributed to individual factors.     

Labeling of phosphatidylcholines of retina subcellular fractions by [1-14C]eicosatetraenoate (20:4(n-6)), docosapentaenoate (22:5(n-3)) and docosahexaenoate (22:6(n-3))

The labeling of molecular species of phosphatidylcholine (PC) has been studied in bovine retinas incubated for 2 h with (1-14C)-labeled (n-6) eicosatetraenoate (n-3) docosapentaenoate and (n-3) docosahexaenoate (20:4, 22:5 and 22:6, respectively) and in four subcellular fractions isolated after such incubations. Of the total radioactivity incorporated in PC, the following percentages of the above fatty acids, respectively, are found in its dipolyunsaturated species: 58, 56 and 53% in rod outer segments; 29, 41 and 49% in mitochondria; 24, 28 and 39% in microsomes; 12, 14 and 16% in postmicrosomal supernatants; 28, 36 and 58% in entire retinas. The remainder percentages are in tetra-, penta- and hexaenoic species of PC, respectively. The levels of pentaenoic species in the PCs of all fractions are similar, while tetraenes are lowest and hexaenes highest in photoreceptor membranes. Dipolyunsaturated species are highly concentrated in photoreceptor membranes, but are minor components of mitochondrial, microsomal and cytosolic PC. The specific radioactivities of tetraenoic, pentaenoic and hexaenoic PCs are decreasingly lower in the following order: postmicrosomal supernatants, microsomes, mitochondria, photoreceptor membranes. In contrast, the specific radioactivities of dipolyunsaturated PCs are higher in mitochondria and microsomes than in the other fractions, especially with 22:5 and 22:6. It is suggested that mitochondria as well as the endoplasmic reticulum could play a role in the synthesis and further modifications of dipolyunsaturated PCs before being supplied to photoreceptor membranes.     

Altered physiological responsiveness and decreased cyclic AMP levels in rat atria after dietary cod liver oil supplementation and its possible association with an increased membrane phospholipid n-3/n-6 fatty acid ratio

Rats were given a cod liver oil supplemented diet and a standard diet for 4 months. The cod liver oil supplementation resulted in a marked increase in the 20:5(n-3) and 22:6(n-3) fatty acids and a marked decrease in the 20:4(n-6) fatty acid in phosphatidylcholine and ethanolamine of the atrial membrane. Atria from the cod liver oil treated rats showed a marked decrease in contractile force, heart rate and cyclic AMP (cAMP) levels under basal conditions. Stimulation with noradrenaline (1 X 10(-6) M) during high oxygen saturation and reoxygenation resulted in an equal increase in the mechanical responses of the two groups in spite of the significantly different levels of cAMP, whereas in hypoxia, both the cAMP level and the contractile force were significantly lower in the cod liver oil treated group. These results indicate that changes in the fatty acid composition of heart membrane phospholipids is associated with changes in adenylate cyclase activity and physiological function of the rat heart and that an increase in the n-3/n-6 fatty acid ratio in membrane phospholipids of the heart results, when oxygen is abundant in enhanced cAMP-independent contractile activity.     

Membrane lipid composition of pancreatic AR42J cells: modification by exposure to different fatty acids

Dietary fat type influences fatty acids in rat pancreatic membranes, in association with modulation of secretory activity and cell signalling in viable acini. We aimed to confirm whether AR42J cells are a valid model to study the interactions between lipids and pancreatic acinar cell function. For this purpose we have (i) compared the baseline fatty acid composition of AR42J cells with that of pancreatic membranes from rats fed a standard chow; (ii) investigated if fatty acids in AR42J membranes can be modified in culture; and (iii) studied if similar compositional variations that can be evoked in rats when dietary fat type is altered occur in AR42J cells. Weaning Wistar rats were fed for 8 weeks either a commercial chow (C) or semi-purified diets containing virgin olive oil (VOO) or sunflower oil (SO) as fat source. AR42J cells were incubated for 72 hrs in medium containing unmodified fetal calf serum (FCS, AR42J-C cells), FCS enriched with 18:1 n-9 (AR42J-O cells), or FCS enriched with 18:2 n-6 (AR42J-L cells). Fatty acids in crude membranes from rat pancreas and AR42J cells were determined by gas-liquid chromatography. Differences in membrane fatty acids between C rats and AR42J-C cells can be explained in part by variations in the amount of fatty acids in the extracellular environment. Supplementation of FCS with 18:1 n-9 or 18:2 n-6 changed the fatty acid spectrum of AR42J cells in a manner that resembles the pattern found, respectively, in VOO and SO rats, although AR42J-L cells were unable to accumulate 20:4 n-6. The AR42J cell line can be a useful tool to assess the effect of membrane compositional changes on acinar cell function. However, differences in baseline characteristics, and perhaps fatty acid metabolism, indicate that results obtained in AR42J cells should be confirmed with experiments in the whole animal.     

Interactions of saturated, n-6 and n-3 polyunsaturated fatty acids to modulate arachidonic acid metabolism

Anti-thrombotic effects of omega-3 (n-3) fatty acids are believed to be due to their ability to reduce arachidonic acid levels. Therefore, weanling rats were fed n-3 acids in the form of linseed oil (18:3n-3) or fish oil (containing 20:5n-3 and 22:6n-3) in diets containing high levels of either saturated fatty acids (hydrogenated beef tallow) or high levels of linoleic acid (safflower oil) for 4 weeks. The effect of diet on the rate-limiting enzyme of arachidonic acid biosynthesis (delta 6-desaturase) and on the lipid composition of hepatic microsomal membrane was determined. Both linseed oil- or fish oil-containing diets inhibited conversion of linoleic acid to gamma-linolenic acid. Inhibition was greater with fish oil than with linseed oil, only when fed with saturated fat. delta 6-Desaturase activity was not affected when n-3 fatty acids were fed with high levels of n-6 fatty acids. Arachidonic acid content of serum lipids and hepatic microsomal phospholipids was lower when n-3 fatty acids were fed in combination with beef tallow but not when fed with safflower oil. Similarly, n-3 fatty acids (18:3n-3, 20:5n-3, 22:5n-3, and 22:6n-3) accumulated to a greater extent when n-3 fatty acids were fed with beef tallow than with safflower oil. These observations indicate that the efficacy of n-3 fatty acids in reducing arachidonic acid level is dependent on the linoleic acid to saturated fatty acid ratio of the diet consumed.