Effect of dietary fats on arachidonic acid and eicosapentaenoic acid biosynthesis and conversion to C22 fatty acids in isolated rat liver cells

The desaturation, chain elongation and esterification of [1-14C]eicosapentaenoic acid, [1-14C]arachidonic acid, [1-14C]eicosatrienoic acid, [1-14C]linolenic acid and [1-14C]linoleic acid were studied in isolated liver cells. Rats fed diets with either 15% hydrogenated coconut oil or 15% partially hydrogenated marine oil, both deficient in essential fatty acids, 15% soybean oil or standard pellet diet with 6% fat, were used. The delta 4-desaturation of 22:5(n - 3) and 22:4(n - 6) as well as the delta 6-desaturase activity was distinctly higher in cells from animals fed coconut or marine oil than with soybean oil or standard pellet. The rate of delta 5-desaturation of 20:3(n - 6) and 20:4(n - 3) was nearly the same in cells from rats fed coconut, marine and soybean oils and higher than with standard pellet. The chain elongation of 20:5(n - 3) to 22:5(n - 3) was distinctly more pronounced than the elongation of 20:4(n - 6) with all four diets. 20:5(n - 3) was mainly esterified in the phospholipids with marine and coconut oils, and mainly in triacylglycerol with standard pellet and soybean oils. The proportion of [1-14C]20:4(n - 6) in the phospholipids to that in triacylglycerol decreased in the order marine oil greater than coconut oil greater than standard pellet greater than soybean oil. The different endogenous arachidonic acid content in the phospholipids induced by the different diets increased in the same order. 20:5(n - 3) was rapidly esterified in triacylglycerol and phospholipids, then liberated especially from the triacylglycerol fraction, chain elongated to 22:5(n - 3) and reesterified.     

Seasonal changes in lipid classes and fatty acid composition in the digestive gland of Pecten maximus

Seasonal variations in lipid classes and fatty acid composition of triacylglycerols and phospholipids in the digestive gland of Pecten maximus were studied over a period of 16 months. Acylglycerols predominated (19-77% of total lipids), in accordance with the role of the digestive gland as an organ for lipid storage in scallops. Seasonal variations were mainly seen in the acylglycerol content, while phospholipids (2.5-10.0% of total lipids) and sterols (1.9-7.4% of total lipids) showed only minor changes. The most abundant fatty acids were 14:0, 16:0, 18:0, 16:1(n-7), 18:1(n-9), 18:1(n-7), 18:4(n-3), 20:5(n-3) and 22:6(n-3) and these showed similar seasonal profiles in both, triacylglycerol and phospholipid fractions. In contrast to the phospholipid fraction, the triacylglycerol fraction contained more 20:5(n-3) than 22:6(n-3). In three phospholipid samples we noted a high percentage of a 22-2-non-methylene-interrupted fatty acid, previously described to have a structural role in several bivalve species. The main polyunsaturated fatty acids displayed important seasonal variations parallel to those of the acylglycerols, suggesting good nutritional conditions. A positive correlation existed between the level of saturated fatty acids and temperature, whereas the levels of polyunsaturated fatty acids correlated negatively with temperature.     

Metabolism of long-chain polyunsaturated fatty acids in isolated cardiac myocytes

The uptake and integrated intracellular metabolism of (n - 6) and (n - 3) polyunsaturated fatty acids was studied in isolated rat cardiac myocytes and in the perfused heart. Labeled linolenic acid (18:3(n - 3)) uptake and its subsequent metabolism into carbon dioxide as well as acylation into lipids was nonsaturable over a substrate range of 0.02 to 0.4 mM. [1-14C]Linoleic acid (18:2(n - 6)), dihomo-gamma-linolenic acid (20:3(n - 6)) and arachidonic acid (20:4(n - 6)) were transported into myocytes at rates similar to those for linolenic acid. Conversely both [1-14C]-gamma-linolenic acid (18:3(n - 6)) and eicosapentaenoic acid (20:5(n - 3)) were taken up at a slower rate. Oxidation of 18:3(n - 6) was 4-5-fold greater when compared with C18-C20 polyunsaturated fatty acids. When myocytes were incubated with labeled 18:2(n - 6), 18:3(n - 6), 18:3(n - 3), 20:4(n - 6) or 20:5(n - 3), it was not possible to detect any desaturation or chain-elongation products. Identical results were obtained when hearts were perfused with 1-14C-labeled linoleic acid.     

Modification of fatty acid composition of membrane phospholipid in hepatocyte monolayer with n-3, n-6 and n-9 fatty acids and its relationship to triacylglycerol production

The objective of these studies with rat hepatocytes in primary culture was to establish that: (a) membrane phospholipids would become enriched with the specific fatty acid supplemented to the media and (b) hepatocyte monolayer triacylglycerol synthetic rates were dependent on the type of fatty acid enrichment of the membrane phospholipids. Hepatocytes cultured in the absence of media lipid developed a phospholipid fatty acid composition which is indicative of an essential fatty acid deficiency. The extensive rise in 18:1(n - 9) content indicated that delta 9-desaturase was active. The fatty acid composition of phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol in the microsomal- and mitochondrial-enriched fractions was highly dependent upon the type of fatty acid supplemented to the medium. Incorporation of fatty acids into phospholipids was rapid, and a new steady-state in fatty acid composition was achieved within approx. 36 h. Changes in the fatty acid composition of these hepatocyte phospholipid subclasses resulting from media supplementation with 18:2/20:4(n-6) or 20:5(n-3) were similar, but not identical, to changes which occurred in vivo as a result of consuming diets rich in 18:2(n-6) or 20:5(n-3). Hepatocyte lipogenesis was highly dependent upon the type of fatty acid supplemented to the medium. Prior conditioning with 16:0 increased triacylglycerol synthesis and secretion. Secretion of triacylglycerol was reduced by polyenoic fatty acid enrichment with 20:5(n-3) greater than 20:4/18:2(n-6). The suppression of triacylglycerol synthesis by 20:5(n-3) was due to an increased (P less than 0.05) diacylglycerol specific activity, which indicates that 20:5(n-3) suppression of hepatic triacylglycerol production may be caused in part by the inhibition of diacylglycerol acyltransferase.     

Phospholipid and triacylglycerol fatty acid content and pattern in the cardiac endothelium of rats depleted in long-chain polyunsaturated omega 3 fatty acids

Rats depleted in long-chain polyunsaturated omega3 fatty acids (omega3-depleted rats) display several features of the metabolic syndrome including hypertension and cardiac hypertrophy. This coincides with alteration of the cardiac muscle phospholipid and triacylglycerol fatty acid content and/or pattern. In the present study, the latter variables were measured in the cardiac endothelium of normal and omega3-depleted rats. Samples derived from four rats each were obtained from 16 female normal fed rats and three groups of 36-40 female fed omega3-depleted rats each aged 8-9, 15-16 and 22-23 weeks. At comparable mean age, the ratio between the square root of the total fatty acid content of phospholipids and cubic root of the total fatty acid content of triacylglycerols was lower in omega3-depleted rats than in control animals. The total fatty acid content of triacylglycerols was inversely related to their relative content in C20:4omega6. Other differences between omega3-depleted rats and control animals consisted in a lower content of long-chain polyunsaturated omega3 fatty acids in both phospholipids and triacylglycerols, higher content of long-chain polyunsaturated omega6 fatty acids in phospholipids, higher activity of delta9-desaturase (C16:0/C16:1omega7 and C18:0/C18:1omega9 ratios) and elongase [(C16:0 + C16:1omega7)/(C18:0 + C18:1omega9) and C20:4omega6/C22:4omega6 ratios], but impaired generation of C22:6omega3 from C22:5omega3 in the former rats. These findings support the view that cardiovascular perturbations previously documented in the omega3-depleted rats may involve impaired heart endothelial function.     

Beta-oxidation of medium chain (C8-C14) fatty acids studied in isolated liver cells

The beta-oxidation and esterification of medium-chain fatty acids were studied in hepatocytes from fasted, fed and fructose-refed rats. The beta-oxidation of lauric acid (12:0) was less inhibited by fructose refeeding and by (+)-decanoyl-carnitine than the oxidation of oleic acid was, suggesting a peroxisomal beta-oxidation of lauric acid. Little lauric acid was esterified in triacylglycerol fraction, except at high substrate concentrations or in the fructose-refed state. With [1-14C]myristic acid (14:0), [1-14C]lauric acid (12:0), [1-14C]octanoic acid (8:0) and [2-14C]adrenic acid (22:4(n - 6] as substrate for hepatocytes from carbohydrate-refed rats, a large fraction of the 14C-labelled esterified fatty acids consisted of newly synthesized palmitic acid (16:0), stearic acid (18:0) and oleic acid (18:1) while intact [1-14C]oleic acid substrate was esterified directly. With [9,10-3H]myristic acid as the substrate, small amounts of shortened 3H-labelled beta-oxidation intermediates were found. With [U-14C]palmitic acid, no shortened fatty acids were detected. It was concluded that when the mitochondrial fatty acid oxidation is down-regulated such as in the carbohydrate-refed state, medium-chain fatty acids can partly be retailored to long-chain fatty acids by peroxisomal beta-oxidation followed by synthesis of C16 and C16 fatty acids which can then stored as triacylglycerol.     

Sex differences in the metabolism of essential fatty acids studied in isolated rat liver cells

The triacylglycerol synthesis from exogenous linoleic acid (18:2(n-6], linolenic acid (18:3(n-3], dihomogammalinolenic acid (20:3(n-6], eicosapentaenoic acid (20:5(n-3] and oleic acid (18:1(n-9] was observed to be significantly increased in isolated liver cells from female rats compared with males. The rate of fatty acid oxidation and phospholipid biosynthesis was concomitantly more important in male cells. With the C22-polyenoic fatty acids, adrenic acid (22:4(n-6] and docosahexaenoic acid (22:6(n-3), only a minor sex-related difference in fatty acid metabolism was found.     

Association of calmodulin inhibition, erythrocyte membrane stabilization and pharmacological effects of drugs

Isolated liver cells from rats fed a diet deficient in essential fatty acids were used to study the oxidation, esterification and, especially, the desaturation and chain elongation of [1-14C]linoleic acid. 14C-labelled arachidonic acid (20:4) and smaller amounts of eicosatrienoic acid (20:3) were recovered mainly in the phospholipids, while gamma-linolenic acid (18:3) was found in both the phospholipids and the triacylglycerol fraction. Lactate strongly increased the formation of arachidonic acid, which was found mainly in the phosphatidylcholine and the phosphatidylinositol fractions. Lactate reduced the amounts of gamma-linolenic acid. Glucagon and (+)-decanoylcarnitine reduced the formation of arachidonic acid, and (+)-decanoylcarnitine increased the incorporation of gamma-linolenic acid especially, in the triacylglycerol fraction. Increasing concentrations of the [1-14C]linoleic acid substrate increased the formation of arachidonic acid and of the other chain-elongated or desaturated fatty acids. Lactate also stimulated the formation of arachidonic acid in liver cells from animals fed adequate amounts of essential fatty acids. It is suggested that dietary and hormonal factors which can change the intracellular levels of malonyl-CoA may influence both the ratio of arachidonic acid/gamma-linolenic acid formed and the total amounts of desaturated and chain-elongated fatty acids formed from linoleic acid.     

De novo biosynthesis of arachidonic acid and 5,11,14-eicosatrienoic acid in the cricket Teleogryllus commodus

The de novo biosynthesis of 5,11,14-eicosatrienoic acid (5,11,14-20:3), arachidonic acid (20:4(n - 6] and eicosadienoic acid (20:2(n - 6] and the elongation/desaturation of linoleic acid (18:2(n - 6] to 20:4(n - 6) and alpha-linolenic acid (18:3(n - 3] to eicosapentaenoic acid (20:5(n - 3] were demonstrated in adult males of the field cricket Teleogryllus commodus. Sodium [1-14C]acetate, [1-14C]18:2(n - 6) and [1-14C]18:3(n - 3) were injected into adult male crickets and after an incubation period, the testes and remaining tissues were extracted and the methyl esters obtained from the phospholipid and triacylglycerol fractions were analyzed. After 5 days of daily injections of [1-14C]acetate, the methyl esters of the triene and tetraene fatty acids from the testicular phospholipid fraction were purified by AgNO3-TLC and HPLC and analyzed by GLC, radio-HPLC, and radio-GLC of ozonolysis products. The results demonstrate the de novo biosynthesis of 20:2(n - 6), 20:4(n - 6) and an isomer of 20:3(n - 6) with double bonds in the 5,11,14 positions. the elongation/desaturation of 18:2(n - 6) to 20:4(n - 6) and 18:3(n - 3) to 20:5(n - 3) was demonstrated by analysis of the methyl esters derived from the testicular phospholipid fraction by radio-HPLC after injecting crickets with radiolabeled substrates.     

Effects of dietary butter enrichment on the fatty acid distribution of phospholipid fractions isolated from rat platelets and aortae

Rats were maintained for 2 weeks on a low-fat basal diet (5% energy) and a diet from which 50% of the energy was derived from butter. Lipids were extracted from aortae and platelets and the fatty acid profiles of individual phospholipids were examined. Similar responses to dietary butter enrichment occurred in PI, PS, PE and PC fractions from either tissue: 20:4(n - 6) and all other n - 6 series longer-chain polyunsaturated fatty acids except 20:3(n - 6) decreased in percentage; all n - 3 series polyunsaturated fatty acids increased, including 20:5(n - 3) and 22:6(n - 3); n - 9 series polyunsaturated fatty acids, derived from 18:1(n - 9), increased. Despite the considerable redistribution of polyunsaturated fatty acids, the percentages of total polyunsaturated fatty acids in each phospholipid were, in every case, independent of diet. None of the changes were localized in a particular phospholipid fraction. Quantitation of fatty acids using heptadecanoic acid as an internal standard revealed that the concentrations of 20:4(n - 6) in platelet and aortic PE and PC was higher than in PI fractions. Therefore, in terms of substrate amount, it appears that PC and PE as well as PI have the potential to provide endogenous 20:4(n - 6) for oxygenation to the prostanoids thromboxane A2 and prostacyclin I2.     

Astrocytes, Not Neurons, Produce Docosahexaenoic Acid (22:6ω-3) and Arachidonic Acid (20:4ω-6)

Elongated, highly polyunsaturated derivatives of linoleic acid (18:2 omega-6) and linolenic acid (18:3 omega-3) accumulate in brain, but their sites of synthesis are not fully characterized. To investigate whether neurons themselves are capable of essential fatty acid elongation and desaturation or are dependent upon the support of other brain cells, primary cultures of rat neurons and astrocytes were incubated with [1-14C] 18:2 omega-6, [1-14C]20:4 omega-6, [1-14C]18:3 omega-3, or [1-14C]20:5 omega-3 and their elongation/desaturation products determined. Neuronal cultures were routinely incapable of producing significant amounts of delta 4-desaturase products. They desaturated fatty acids very poorly at every step of the pathway, producing primarily elongation products of the 18- and 20-carbon precursors. In contrast, astrocytes actively elongated and desaturated the 18- and 20-carbon precursors. The major metabolite of 18:2 omega-6 was 20:4 omega-6, whereas the primary products from 18:3 omega-3 were 20:5 omega-3, 22:5 omega-3, and 22:6 omega-3. The majority of the long-chain fatty acids formed by astrocyte cultures, particularly 20:4 omega-6 and 22:6 omega-3, was released into the extracellular fluid. Although incapable of producing 20:4 omega-6 and 22:6 omega-3 from precursor fatty acids, neuronal cultures readily took up these fatty acids from the medium. These findings suggest that astrocytes play an important supportive role in the brain by elongating and desaturating omega-6 and omega-3 essential fatty acid precursors to 20:4 omega-6 and 22:6 omega-3, then releasing the long-chain polyunsaturated fatty acids for uptake by neurons.     

Comparative utilization of n-3 polyunsaturated fatty acids by cultured human Y-79 retinoblastoma cells

The Y-79 retinoblastoma cell, a cultured human line derived from the retina, was utilized as a model for investigating the metabolism of n-3 polyunsaturated fatty acids in neural tissue. When cultures were incubated with 5 microM linolenic (18:3), eicosapentaenoic (20:5) or docosahexaenoic (22:6) acids, a low concentration probably representative of physiologic levels, the amount incorporated was 20:5 congruent to 18.3 greater than 22:6. Regardless of which fatty acid was provided, 65-75% of the total uptake accumulated in phosphatidylethanolamine and ethanolamine plasmalogen, suggesting that these phospholipids play an important role in n-3 polyunsaturated fatty acid metabolism. A small amount of 22:6 was converted to 20:5, which was recovered in phosphatidylinositol and phosphatidylserine. Therefore, one metabolic function of 22:6 may be to serve as an intracellular storage pool for the formation of 20:5 through retroconversion. When any of the n-3 polyunsaturates was available, the main fatty acid that accumulated in the cell phospholipids was 22:6. The extent to which 22:6 accumulated, however, depended on the particular n-3 polyunsaturated fatty acid that was available. This suggests that the 22:6 content of a neural cell, and any cellular function dependent on 22:6 content, may be regulated by changes in the type of n-3 polyunsaturate available to the nervous system.     

Regional differences in lipid composition and incorporation of saturated and unsaturated fatty acids into microsomal membranes of rat small intestine

Incorporation of [1-14C]palmitic (16:0) and [1-14C]linoleic (18:2 omega 6) acids into microsomal membranes of proximal (jejunum) and distal (ileum) regions of rat small intestine was investigated, and the lipid composition, including fatty acid profiles of membrane phospholipids, was determined. Jejunal microsomes contained significantly higher amounts of total phospholipids, phosphatidylcholine, and phosphatidylinositol, and lower amounts of cholesterol and sphingomyelin when compared with ileal microsomes. Jejunal microsomal phospholipids contained higher levels of stearic (18:0), 18:2 omega 6, and eicosapentaenoic (20:5 omega 3) acids followed by reduced levels of oleic (18:1 omega 9), arachidonic (20:4 omega 6), and docosahexaenoic (22:6 omega 3) acids when compared with those from the ileum, except for phosphatidylinositol where no significant difference between 20:4 omega 6 content of each site was observed. In both jejunal and ileal microsomes, incorporation of [1-14C]18:2 omega 6 was significantly higher than that of [1-14C]16:0. Incorporation of both [1-14C]16:0 and [1-14C]18:2 omega 6 was significantly higher in jejunal microsomal lipid fractions (phospholipids, diacylglycerols, triacylglycerols) when compared with the ileal microsomal fraction. These data suggest that (1) jejunal and ileal microsomal membranes differ from each other in terms of lipid composition and lipid synthesis, (2) site variations in the specificity of acyltransferases for different fatty acids exist, and (3) higher delta 9-, delta 6-, delta 5-, and delta 4-desaturase activities exist in ileal compared with jejunal enterocytes.     

Mitochondrial and peroxisomal oxidation of arachidonic and eicosapentaenoic acid studied in isolated liver cells

The partitioning between peroxisomal and mitochondrial beta-oxidation of [1-14C]eicosapentaenoic acid (20:5(n-3] and [1-14C]arachidonic acid (20:4(n-6)) was studied. In hepatocytes from fasted rats approximately 70% of the fatty acid substrate was oxidized with oleic, linoleic, eicosapentaenoic and docosahexaenoic (22:6(n-3)) acid, even more with adrenic (22:4(n-6)) and less with arachidonic acid. When the mitochondrial oxidation was suppressed by fructose refeeding and by (+)-decanoylcarnitine, the fatty acid oxidation in per cent of that in cells from fasted rats was with 18:1(n-9) 7%, 18:2(n-6) 8%, 20:4(n-6) 12%, 20:5(n-3) 20%, 22:4(n-6) 57% and for 22:6(n-3) 29%. The fraction of 14C recovered in palmitate and other newly synthesized fatty acids after fructose refeeding decreased in the order 22:4(n-6) greater than 22:6(n-3) greater than 20:5(n-3) greater than 20:4(n-6) and was very small with 18:1(n-9) and 18:2(n-6). In cells from both fed and fructose-refed animals 20:5(n-3) was efficiently elongated to 22:5(n-3) and 22:6(n-3). 20:5(n-3) and 20:4(n-6) were not elongated after fasting. The phospholipid incorporation with [1-14C]20:5(n-3) decreased during prolonged incubations while it remained stable with [1-14C]arachidonic acid. The results suggest that peroxisomes contribute more to the oxidation of 20:5(n-3) than with 20:4(n-6) although both substrates are probably oxidized mainly in the mitochondria.     

22-Carbon polyenoic acids. Incorporation into platelet phospholipids and the synthesis of these acids from 20-carbon polyenoic acid precursors by intact platelets

The types of unsaturated fatty acids found in platelet phospholipids must be regulated by a series of controls which include specificity for activation and acylation as well as modification of circulating fatty acids by platelets prior to incubation into phospholipids. In this study we show that washed human platelets not only incorporate [1-14C]6,9,12-18:3, [1-14C]6,9,12,15-18:4, [1-14C]5,8,11-20:3, [1-14C]5,8,11,14-20:4, and [1-14C]5,8,11,14,17-20:5 into their phospholipids but also chain elongate each of these acids with subsequent acylation of the chain elongated products into phospholipids. Platelets incubated alone with 1-14C-labeled 5,8,11-20:3, 5,8,11,14-20:4, 5,8,11,14,17-20:5, 7,10,13,16,19-22:5, or 4,7,10,13,16,19-22:6 incorporated each of these acids into individual phosphoglycerides with phosphatidylinositol having the highest specific activity followed by phosphatidylcholine with phosphatidylserine approximately equal to phosphatidylethanolamine. The incorporation specificity of 4,7,10,13,16,19-22:6 was atypical since it was a relatively poor substrate for acylation into all phospholipids except phosphatidylethanolamine. The 20-carbon acids were better substrates for incorporation into phospholipids than were the 22-carbon compounds. Simultaneous incubation of 10 microM [1-14C]5,8,11,14-20:4 with increasing levels (5 to 15 microM) of each of the above five other 1-14C-labeled acids showed a concentration-dependent increase in the amount of the second fatty acid incorporated into platelet phospholipids. Dietary fat modification thus has the potential of increasing the plasma pool of 22-carbon acids for incorporation into platelets. In addition the activation of 20-carbon eicosanoid precursors by the high affinity platelet activating enzyme (Wilson, D. B., Prescott, S. M. and Majerus, P. W. (1982) J. Biol. Chem. 257, 3510-3515) will yield an acyl-CoA for both acylation and chain elongation followed by subsequent incorporation of 22-carbon acids into phosphoglycerides.     

The biosynthesis of docosahexaenoic acid [22:6(n-3)] from linolenic acid in primary hepatocytes isolated from wild northern pike

Primary hepatocytes from wild northern pike Esox lucius were incubated with radiolabelled linolenic acid ([l-¹⁴C]-18:3(n-3)) to assess their ability to synthesize docosahexaenoic acid [22:6(n-3)]. The distribution of radioactivity in lipid classes and hepatocyte polyunsaturated fatty acids (PUFA) was measured over the time-course of 24h. The majority of radioactivity from [l-¹⁴C]-18:3(n-3) was recovered in hepatocyte triacylglycerols (TAG) and phosphatidylcholine (PC). The levels of radioactivity in TAG and in most of phospholipids, including PC, increased significantly over the incubation period. Radioactivity from [1-¹⁴C]-18:3(n-3) was recovered in several hepatocyte PUFA, including 22:6(n-3), and the Δ6 and Δ5-desaturation products 18:4(n-3) and 20:5(n-3). The presence of radioactivity in C₂₄ (n-3) PUFA may be evidence that the biosynthesis of 22:6(n-3) in pike proceeds via a pathway independent of Δ4-desaturation. Analysis by radio gas chromatography revealed that radiolabelled 24:6(n-3) was present among the desaturation and elongation products of [l-¹⁴C]-18:3(n-3). The results establish that, under the in vitro conditions employed, pike hepatocytes are able to convert linolenic acid to 20:5(n-3) and 22:6(n-3).     

Effects of clofibrate feeding on essential fatty acid desaturation and oxidation in isolated rat liver cells.

The effects of clofibrate feeding on the metabolism of polyunsaturated fatty acids were studied in isolated rat hepatocytes. Administration of clofibrate stimulated the oxidation and particularly the peroxisomal beta-oxidation of all the fatty acids used. The increase in oxidation products was markedly higher when n-3 fatty acids were used as substrate, indicating that peroxisomes contribute more to the oxidation of n-3 than n-6 fatty acids. The whole increase in oxidation could be accounted for by a corresponding decrease in acylation in triacylglycerol while the esterification in phospholipids remained unchanged. A marked stimulation of the amounts of newly synthesized C16 and C18 fatty acids recovered, was observed when 18:2(n-6), 20:3(n-6), 18:3 (n-3) and 20:5(n-3), but not when 20:4(n-6) and 22:4(n-6) were used as substrate. This agrees with the view that extra-mitochondrial acetyl-CoA produced from peroxisomal beta-oxidation is more easily used for fatty acid new synthesis than acetyl-CoA from mitochondrial beta-oxidation. The delta 6 and delta 5 desaturase activities were distinctly higher in cells from clofibrate fed rats indicating a stimulating effect.     

Acylation of 1-palmitoyl-sn-glycerophosphocholine by chick brain microsomes is unaffected by fatty acid binding protein

Rates of incorporation of exogenously supplied fatty acids into 1-palmitoyl-sn-glycerophosphocholine were measured using the microsomal fraction from brains of 14–15 day old chick embryos. The substrate preferences for reacylation were: 18: 2(n – 6) = 20: 4(n – 6) 20: 5(n – 3) = 18: 3(n – 3) 18 : 1(n – 9) 22: 6(n – 3) 18: 0. The normalized rate with 18: 0 was significantly lower than all other rates except for 22: 6(n – 3), and the acylation rate with 22: 6(n – 3) was significantly lower than with 18: 2(n – 6) and 20: 5(n – 3). With the addition of fatty acid binding protein partially purified from brain cytosol, a decrease (not significant) in the rate of incorporation was observed; the substrate preference was unchanged. In the presence of FABP, normalized rates with 18: 2(n – 6) were significantly higher than with 18: 0, 18: 1(n – 9), or 22: 6(n – 3); rates with 20: 4(n - 6) were significantly higher than those with 22: 6(n – 3). Preliminary data on the acylation of 1-palmitoyl-sn-glycerophosphoethanolamine showed lower rates of incorporation than for the choline analogue and no clear substrate preference, but a similar lack of effect of fatty acid binding protein. These results do not support the proposed function of fatty acid binding protein in the establishment of a phospholipid composition rich in polyunsaturated fatty acids. The results are consistent, however, with the role of the reacylation reaction in the continual turnover of particular substrates [18: 2(n – 6) and 20: 4(n – 6)] used to generate second messengers.Abbreviations GPC Glycerophosphocholine - GPE Glycerophosphoethanolamine - LPC 1-palmitoyl-sn-glycerophosphocholine - LPE 1-palmitoyl-sn-glycerophosphoethanolamine - PUFA Polyunsaturated Fatty Acids - FABP Fatty Acid Binding Protein     

Sex, but not maternal protein or folic acid intake, determines the fatty acid composition of hepatic phospholipids, but not of triacylglycerol, in adult rats

The aim of the study was to investigate whether the protein and folic acid content of the maternal diet and the sex of the offspring alter the polyunsaturated fatty acid content of hepatic phospholipids and triacylglycerol (TAG). Pregnant rats were fed diets containing 18% or 9% protein with either 1 or 5mg/kg folic acid. Maternal diet did not alter hepatic lipid composition in the adult offspring. Data from each maternal dietary group were combined and reanalysed. The proportion of 18:0, 20:4n-6 and 22:6n-3 in liver phospholipids was higher in females than in males, while hepatic TAG composition did not differ between sexes. Delta5 Desaturase expression was higher in females than in males. Neither Delta5 nor Delta6 desaturase expression was related to polyunsaturated fatty acid concentrations. These results suggest that sex differences in liver phospholipid fatty acid composition may reflect primary differences in the specificity of phospholipid biosynthesis.     

Effects of hypothyroidism on the distribution and fatty acyl composition of phospholipids in sarcoplasmic reticulum of fast skeletal muscle of the rat

The distribution of phospholipids and fatty acyl composition of individual phospholipids in sarcoplasmic reticulum from fast skeletal muscle of hypothyroid and euthyroid (control) rats have been determined. Hypothyroidism resulted in a 24% decrease in the phosphatidylethanolamine (PE) content and a concomitant increase in the phosphatidylcholine (PC) content of the sarcoplasmic reticulum. The amounts of other phospholipids and cholesterol remained unaffected. Fatty acyl compositions of PE and PC were quantitatively different, but hypothyroidism affected these compositions similarly. Changes included an increase in the proportions of docosahexaenoic (22:6(n - 3)), arachidonic (20:4(n - 6)), icosatrienoic (20:3(n - 6)) and stearic (18:0) acids and a decrease in those of linoleic (18:2(n - 6)), palmitic (16:0) and oleic (18:1(n - 9)) acids. The effects of hypothyroidism on the phospholipid distribution could be reversed by treatment of hypothyroid animals with thyroid hormone for a period of 14 days (10 micrograms T3/100 g body weight per 2 days). The fatty acyl composition of the phospholipids was also restored to the euthyroid values by this treatment. Exceptions were 18:2 and 22:6 in PE, in which case reversal was significant but not complete, and 18:2, 20:4 and 22:6 in PC. The levels of these acids in PC were not reversed to the euthyroid values after the 14-day treatment, but rather the opposite occurred.