Influence of dietary n-3 fatty acids on the membrane properties of skeletal muscle in pigs

The aim of the experiment was the in vivo modification of long-chain fatty acids in phospholipids and to investigate the impact on Ca²⁺ transport of sarcoplasmic reticulum (SR). Ten pigs were fed daily a diet containing 1.3 g n-3 fatty acids/kg diet (control), and ten pigs were fed a diet containing 14 g n-3 fatty acids/kg diet (n-3 diet) during the growing-finishing period. The intake of dietary n-3 fatty acids increased the percentages of these fatty acids in the phospholipids of skeletal muscle sarcoplasmic reticulum (21.6% n-3 fatty acids) and in the polar fraction of total muscle homogenates (30.7% n-3 fatty acids) significantly, compared with control (3.0% and 3.9% n-3 fatty acids, respectively), while the n-6 fatty acid concentration was reduced. In phosphatidylethanolamine of skeletal muscle polar lipids eico-sapentaenoic (EPA) and docosahexaenoic acids (DPA) were increased seven times compared with control. There were no differences in the maximal rate of Ca²⁺ uptake in skeletal muscle SR between the groups. However, the activity of Ca²⁺-ATPase of skeletal muscle SR was elevated in the n-3 diet group. It is suggested, that n-3 fatty acid enriched diet can change the complex membrane composition dependent on experimental conditions and animal species leading to different effects on membrane protein activities.     

Phospholipid fatty acid composition in type I and type II rat muscle

The fatty acid composition of the membrane phospholipids phosphatidylcholine (PC) and phosphatidylethanolamine in insulin-sensitive Type I (soleus) and insulin-resistant Type II (EDL) muscle is not known. In the present studies, soleus and EDL muscles were removed from 250–300 g Sprague-Dawley rats, and the fatty acid composition of total and individual phospholipid (PL) species was quantitated. As expected, triglyceride content was increased twofold in soleus muscle. No quantitative differences in the individual PL species or cholesterol content were found between the two muscles. However, a striking difference in PL fatty acid composition was observed in the PC fraction. An increase in 16∶0 with decreases in 18∶0, 18∶1, 22∶5n-3, and 22∶6n-3 (P<0.001 for each) was observed in the PC fraction of EDL compared to that from soleus, consistent with reduced elongation of PC fatty acids. Inhibition of fatty acid oxidation with the carnitine palmitoyl transferase-1 inhibitor, etomoxir, did not alter the fatty acid pattern in either muscle. We conclude that an alteration in PL fatty acid composition consistent with reduced elongation of both saturated and unsaturated fatty acids is observed in Type II muscle. The restriction of these alterations to the PC fraction has important implications. Deceased (June 28, 1996).     

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

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

Isolation of Sarcolemmal Plasma Membranes by Mechanically Skinning Rat Skeletal Muscle Fibers for Phospholipid Analysis

Membrane phospholipid (PL) composition has been shown to affect cellular function by altering membrane physical structure. The sarcolemma plasma membrane (SL_pm) is integral to skeletal muscle function and health. Previous studies assessing SL_pm PL composition have demonstrated contamination from transverse (t)-tubule, sarcoplasmic reticulum, and nuclear membranes. This study assessed the possibility of isolating SL by mechanically skinning skeletal muscle fiber segments for the analysis of SL_pm PL composition. Mechanically skinned SL_pm from rat extensor digitorum longus (EDL) muscle fibers underwent Western blot analysis to assess contamination from t-tubule, sarcoplasmic reticulum, nuclear and mitochondrial membranes. The results indicate that isolated SL_pm had minimal nuclear and mitochondrial membrane contamination and was void of contamination from sarcoplasmic reticulum and t-tubule membranes. After performing both high-performance thin layer chromatography and gas chromatography, we found that the SL_pm obtained by mechanical skinning had higher sphingomyelin and total fatty acid saturation and lower phosphatidylcholine when compared to previous literature. Thus, by avoiding the use of various chemical treatments and membrane fractionation, we present data that may truly represent the SL_pm and future studies can use this technique to assess potential changes under various perturbations and disease conditions such as insulin resistance and muscular dystrophy.     

Inhibition of Mouth Skeletal Muscle Relaxation by Flavonoids of Cistus ladanifer L.: A Plant Defense Mechanism Against Herbivores

Cistus ladanifer exudate is a potent inhibitor of the sarcoplasmic reticulum Ca2+-ATPase (Ca2+-pump) of rabbit skeletal muscle, a well-established model for active transport that plays a leading role in skeletal muscle relaxation. The low concentration of exudate needed to produce 50% of the maximum inhibition of the sarcoplasmic reticulum Ca2+-ATPase activity, 40-60 microg/ml, suggests that eating only a few milligrams of C. ladanifer leaves can impair the relaxation of the mouth skeletal muscle of herbivores, as the exudate reaches up to 140 mg/g of dry leaves in summer season. The flavonoid fraction of the exudate accounts fully for the functional impairment of the sarcoplasmic reticulum produced by the exudate (up to a dose of 250-300 microg/ml). The flavonoids present in this exudate impair the skeletal muscle sarcoplasmic reticulum function at two different levels: (i) by inhibition of the Ca2+-ATPase activity, and (ii) by decreasing the steady state ATP-dependent Ca2+-accumulation. Among the exudate flavonoids, apigenin and 3,7-di-O-methyl kaempferol are the most potent inhibitors of the skeletal muscle sarcoplasmic reticulum. We conclude that the flavonoids of this exudate can elicit an avoidance reaction of the herbivores eating C. ladanifer leaves through impairment of mouth skeletal muscle relaxation.     

Effects of fructose and troglitazone on phospholipid fatty acid composition in rat skeletal muscle

Skeletal muscle phospholipid fatty acid (PLFA) composition is associated with insulin sensitivity in animal models and in man. However, it is not clear whether changes in insulin sensitivity cause a change in PLFA composition or vice versa. The present studies have examined the effects of agents known to increase or decrease insulin sensitivity on PLFA composition of the major phospholipids, phosphatidylcholine (PC) and phosphatidylethanolamine (PE), in soleus and extensor digitorum longus muscle. Four groups of Sprague-Dawley rats— control, 0.2% troglitazone (Tgz), 60% fructose fed, and fructose + Tgz—were treated for 3 wk. Fructose feeding was associated with a decrease in muscle membrane polyunsaturated fatty acids (PUFA) and n-3 fatty acids in both PC and PE. Administration of Igz alone resulted in an increase in liver (3.75±0.93 to 6.93±1.00 μmol/min/mg tissue, P<0.05) and soleus muscle (0.34±0.03 to 0.67±0.09 μmol/min/mg, P<0.01) elongase activity, which would be expected to increase membrane PUFA. However, Tgz decreased PLFA associated with greater insulin sensitivity (e.g., PUFA and n-3 fatty acids) and increased PLFA associated with decreased insulin sensitivity (16∶0 and n-6 fatty acids) in both PC and PE. Co-administration of fructose and Tgz did not reverse the decrease in PUFA observed with fructose alone. We conclude that the improvement in insulin sensitivity reported with Tgz is associated with an apparently paradoxical effect to decrease PUFA and n-3 PLFA composition in rat skeletal muscle. These studies suggest that Tgz-mediated increases in insulin sensitivity do not result in improved PLFA composition.     

Lipids of human myocardium

The major lipid classes, including some phospholipids, and their fatty acid profiles have been measured in portions of left ventricular muscle and psoas muscle obtained at autopsy. Atrial appendages and ventricular muscle removed during cardiac surgery were examined also. The proportions of the individual phospholipids were the same in all the muscles, having an excess of phosphatidyl ethanolamine and phosphatidyl serine compared with the serum. Their fatty acid profiles resembled those obtained from other locations. The triglyceride content of the myocardium was relatively constant (except in the atrial appendage) but did rise slightly with increasing obesity. The free fatty acid concentration in the myocardium was relatively high and had a variable fatty acid profile.     

Lipoprotein lipase in rats fed fish oil: Apparent relationship to plasma insulin levels

To investigate the role of lipoprotein lipase (LPL) and hepatic lipase in the triacylglycerol lowering effects of fish oil, rats were fed lard (L), corn oil (CO) or menhaden oil (MO) as the primary fat source in otherwise identical diets. After 2 weeks, soleus muscle LPL differed between groups (MO>CO>L). Hepatic lipase did not differ between CO- and MO-fed rats but was elevated in L-fed rats. Adipose LPL did not differ between diet groups. Total epididymal fat weight was reduced in MO-fed rats. There was a significant positive correlation between adipose tissue weight and plasma free fatty acids. MO-fed rats had lower plasma insulin levels. Insulin was directly correlated with plasma triacylglycerol and glucose, consistent with a hyperinsulinemic, insulin-resistant state in CO-and L-fed rats, and a protective effect with MO feeding. In addition, insulin was directly correlated with adipose LPL. A negative relationship between soleus muscle LPL and insulin approached significance. Soleus muscle LPL was significantly inversely correlated with triacylglycerol. The data indicate that increased skeletal muscle LPL, in response to MO or a MO-induced decrease in insulin, may contribute to the triacylglycerol-lowering effects of fish oil. Decreased fat weight and adipose LPL and increased soleus muscle LPL and decreased plasma triacylglycerol suggest a shift from fat deposition to oxidation with MO feeding. The lack of response of hepatic lipase to MO feeding suggests that this enzyme does not contribute to the fish oil-stimulated lowering of plasma triacyglycerolvia hepatic reuptake of very low density lipoproteins or other triacylglycerol-rich lipoproteins.     

The effect of antioxidant deficiency on tissue lipid composition in the rat. I. Gastrocnemius and quadriceps muscle

The gastrocnemius and quadriceps muscle phospholipids of the antioxidant-deficient rat fed a source of both linoleate and linolenate showed a progressive net increase in arachidonate, a progressive net decrease in all other polyunsaturated fatty acids, and there was a concomitant accumulation of fluorescent pigment of the lipofuscin or ceroid type in the tissue. An increased incorporation of intraperitoneally injected, isotopically labeled acetate into not only arachidonate but also the other higher polyunsaturated fatty acids, was observed. The net loss of the higher polyunsaturated fatty acids from the membrane lipids (presumably via lipid peroxidation) apparently was partially compensated by a homeostatic mechanism which involved conversion of the available precursors, linoleate and linolenate, to the higher polyunsaturated fatty acids. The rates of decrease of the polyunsaturated fatty acids in the muscle phospholipids and accumulation of fluorescent pigment in the tissue were correlated with the rate of production of creatinuria.     

Lipid components and enzymatic hydrolysis of lipids in muscle of Chinese freshwater fish

The lipid and fatty acid composition of muscle of 10 species of freshwater fish obtained from a market of Shanghai City was examined. Total lipids (TL) ranged over 0.9–4.7% of muscle for all samples. The content of triacylglycerol (TG) in muscle ranged over 0.2–3.4% and that of polar lipids (PL) was 0.5–1.3%. Differences of TL content were dependent on TG contents. The predominant important fatty acids (>10% of the total fatty acids in TL) were 16∶0 and 18∶1n−9 with some 16∶1n−7, 18∶2n−6, and 22∶6n−3. The polyunsaturated fatty acids (PUFA) content was 10.2–43.4%, and especially Chinese sea bass contained above 20% of 22∶6n−3 in the total fatty acids. There were higher levels of PUFA such as 20∶5n−3 and 22∶6n−3 in PL than in neutral lipids. Muscle of the silver carp was stored at 20°C, and changes of lipid classes during storage were examined. Free fatty acids increased, and PL decreased during storage. This phenomenon was inhibited by heating the muscle, suggesting that lipid hydrolysis by phospholipase occurred in silver carp muscle.     

Composition and structure of phospholipids in chicken muscle tissues

Lipids extracted from breast muscle and thigh muscle of one-year old chickens on a standard MSU-Z-4 diet have been fractionated by silicic acid column chromatography into nonphospholipids, phosphatidyl ethanolamine, phosphatidyl serine, phosphatidyl choline (lecithin), and sphingomyelins. Phospholipid fractions were identified by thin-layer chromatography and the quantity of each determined by gravimetric analysis, analysis of the phosphorus content, and infrared spectra. The phospholipid content of thigh muscle (dark meat) lipids was higher than that in the breast muscle (white meat). Phosphatidyl choline and phosphatidyl ethanolamine were found in relatively greater amts than phosphatidyl serine and sphingomyelins. Enzymatic hydrolysis followed by gas-liquid chromatographic analysis of the fatty acids liberated and those in the lysocompounds was used to establish the positional specificity of the fatty acids in the phosphoglycerides. The polyunsaturated fatty acids are located primarily at the β-position and the saturated fatty acids at the α′-position. The qualitative and quantiative determination of the plasmalogens was also accomplished. Michigan Agriculture Experiment Station Journal Article No. 3527. Presented at the AOCS Meeting in Chicago, October, 1964.     

Characteristics of carcass composition,fat metabolism and meat quality of genetically different pigs

The aim of the study was to quantify the differences in meat and fat quality and lipid metabolism of pigs with either high or medium capacity for lipid accretion. A total of 58 castrated males of the breeds German Saddle Back (SB) and German Landrace (DL) were included in the experiment. Animals were housed individually and fed twice daily semi ad libitum. Saddle Back pigs indicated a lower lean meat content (41.4% vs 52.6%) and a higher fat percentage (40.9% vs 28.2%) in comparison to DL as a result of high lipid accumulation. The larger fat content of SB was related to an increased intramuscular fat concentration of longissimus muscle. A significant correlation between intramuscular fat content and fatty acid composition was estimated in both breeds. The relative concentration of saturated fatty acids was significantly increased in SB pigs. The percentage of polyunsaturated fatty acids (8.3%) in SB muscle fat was significantly lower than in DL muscle fat (10.7%). The de novo biosynthesis of fatty acids resulted in mostly saturated fatty acids and oleic acid. The higher activities of lipogenetic enzymes in backfat of SB proved a higher lipogenetic capacity. There were no significant differences in meat quality traits of longissimus muscle between the two breeds.     

Effect of increasing the level of ω-3 fatty acids on rat skeletal muscle sarcoplasmic reticulum

The effect of dietary supplementation with fish oil as compared to corn oil on the lipid dynamics and calcium ATPase activity of rat skeletal sarcoplasmic reticulum was examined. After four-week supplementation with fish oil, the levels of eicosapentaenoic (20∶5ω3), docosapentaenoic (22∶5ω3) and docosahexaenoic (22∶6ω3) acids in the total lipids were 5.3, 5.5 and 28.1% of the total fatty acids, respectively. In contrast, with corn oil only 22∶6 was found (8.9%). The level of these fatty acids in phosphatidylethanolamine from the membranes of animals fed fish oil was 4.2 (20∶5), 5.4 (22∶5) and 49.1% (22∶6); and for phosphatidylcholine it was 5.4 (20∶5), 4.6 (22∶5) and 17.4% (22∶6). Again, in corn oil fed animals, only 22∶6 was found in appreciable amounts, namely 28.3% in phosphatidylethanolamine and 1.8% in phosphatidylcholine. The steady state fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH) was used to assess lipid order and was found to be only slightly less for membranes from animals supplemented with fish oil (0.120) as compared to those supplemented with corn oil (0.124). The calcium ATPase was found to be unaffected by supplementation consistent with the observed modest changes in lipid order as well as with suggestions that the enzyme is relatively insensitive to the level of unsaturation. It could be argued that if large increases in fatty acyl polyunsaturation in mammalian cell membranes would lead to marked alterations in bulk membrane lipid motional properties, this may not be in the interest of preserving physiological function. The complex mixture of phospholipid molecular species present in natural membranes may buffer against this by a type of passive adaptation, without the expenditure of metabolic energy, thus providing a homeoviscous environment able to optimally support membrane protein function.     

Functional diversity of the phosphoglucomutase superfamily: structural implications

Three-dimensional structural models of three members of thephosphoglucomutase (PGM) superfamily, parafusin, phosphoglucomutase-relatedprotein and sarcoplasmic reticulum phosphoglucomutase, wereconstructed by homology modeling based on the known crystalstructure of rabbit muscle phosphoglucomutase. Parafusin, phosphoglucomutase-relatedprotein and sarcoplasmic reticulum phosphoglucomutase each have50% or more identity with rabbit muscle phosphoglucomutase atthe amino acid level and all are reported to exhibit no or minorphosphoglucomutase activity. There are four major insertionsand two deletions in the parafusin sequence relative to PGM,all of which are located in surface-exposed loops connectingsecondary structural elements. The remaining amino acid substitutionsare distributed throughout the sequence and are not predictedto alter the polypeptide fold. Parafusin contains a putativeprotein kinase C site located on a surface loop in domain IIthat is not present in the homologs. Although the general domainstructure and the active site of rabbit muscle phosphoglucomutaseare preserved in the model of phosphoglucomutase-related protein,a major structural difference is likely to occur in domain 1due to the absence of 55 amino acid residues in PGM-RP. Thisdeletion predicts the loss of three -helices and one ß-strandfrom an anti-parallel ß-sheet in this domain as comparedwith the rabbit muscle phosphoglucomutase.     

Effect of brominated vegetable oils on heart lipid metabolism

Normal rats fed for 105 days on an experimental diet made up of standard laboratory chow supplemented with 0.5% of a mixture of brominated sunflower-olive oil (BVO) developed a significant increase in the triacylglycerol content of the heart, liver and soleus muscle compared to controls. In addition, BVO-treated rats had a decrease in plasma levels of triacylglycerol and total and HDL cholesterol. Plasma fatty acid levels and plasma post-heparin lipolytic activities, such as H-TGL, LPL, T-TGL and MGH were similar to those of control animals fed the standard chow alone. Heart PDH_a (active portion of pyruvate dehydrogenase) was dramatically decreased in the BVO-fed rats. A faster rate of spontaneous lipolysis was recorded in the isolated perfused preparation of hearts from the experimental animals. The addition of 10⁻⁷ M of glucagon to the perfusate, however, revealed a lipolytic effect comparable to the one observed in the control rats. In summary, our findings of normal fatty acids and low triacylglycerol plasma levels associated with normal activities of the various PHLA (post-heparin lipolytic activity) enzymes suggest that accumulation of triacylglycerol in heart muscle may not be explained essentially in terms of an elevated uptake and/or increased delivery of plasma fatty acids or plasma triacylglycerol. A decreased in situ catabolism of tissue triacylglycerol also appears unlikely because the spontaneous as well as the glucagon induced lipolysis in the heart both were found to be unimpaired. Our results suggest that the mechanisms involved in the toxicologic effects of a BVO diet on heart lipid metabolism could be exerted mainly at the level of triacylglycerol biosynthesis rather than a derangement in some known step of their catabolic pathway. Additional studies are necessary to clarify this matter. An abstract pertaining to this work was presented in November 1984 at the IV Congress of the Pan American Association of Biochemical Societies (PAABS), Buenos Aires, Argentina.     

Color and the lipid composition of pork muscles

The lipid characteristics of three porcine muscles were investigated. Included in the study were the light and dark portions of the semitendinosus muscle, the semimembranosus (light) and the quadriceps femoris (dark) muscles. The lipids from the semimembranosus and the quadriceps femoris muscles were observed to be statistically different. The light muscles were 20% higher in lipid level and these lipids contained 20% more glycerides and 40% less phospholipids than the dark muscles. The glycerides from both muscle lipids were identical in fatty acid composition but the phospholipid fatty acids differed significantly. The light muscle phospholipid fatty acids were higher in monoenes while the dark muscle phospholipids predominated in polyunsaturates. In the semitendinosus muscle, the light portion was 35% higher in lipid content than the dark portion but the compositions of the lipids from both areas were similar. When these data were compared to the values for the semimembranosus and the quadriceps femoris muscle lipids, the lipid characteristics were found to be intermediate of predominantly light or dark muscle lipids. Presented at the AOCS Meeting, New York, October 1968. E. Utiliz. Res. Dev. Div., ARS, USDA.     

Dietary Inclusion of Tea Catechins Changes Fatty Acid Composition of Muscle in Goats

This study was conducted to examine dietary tea catechins (TC) supplementation on the fatty acid composition of muscle and ruminal bacteria in goats fed a maize stover-based diet. Forty goats, 8 months old (16.2 ± 1.2 kg), were randomly divided into four equal groups (10 animals in each group) and assigned to four experiment diets with TC supplementation at four levels (0, 2,000, 3,000 and 4,000 mg TC/kg feed, namely TC0, TC2000, TC3000 and TC4000, respectively). After a 60-day feeding period, all the goats were slaughtered and sampled. The results showed that dietary TC inclusion increased the average daily gain (ADG), protein content in the semimembranosus muscle and dry matter in the longissimus dorsi muscle (LD). Dietary TC supplementation increased the ratio of n-6 to n-3 fatty acid, the ratio of polyunsaturated fatty acids to saturated fatty acids was higher in TC3000 and TC4000 than in TC0 and TC2000 for LD. The current results implied that dietary inclusion of a suitable TC dose could improve the growth performance and increase the proportions of unsaturated fatty acids in muscle, and the biohydrogenation of ruminal microorganisms might change the profiles of fatty acids in the muscle of growing goats.     

Aspects of Positional Distribution of Fatty Acids in Triacylglycerols of Skin,White and Dark Muscle of Mackerel Scomber scombrus in Relation to Hypertension

The triacylglycerols from skin, white and dark muscle of Atlantic mackerel Scomber scombrus were isolated and the distribution of fatty acids on the glycerol examined with pancreatic lipase. The dark muscle, which is the smallest dietary fat source of the three tissues, had less EPA and more DHA than the other two tissues. The EPA deficiency was located in the 2-position. The DHA was similar in both the 2-and 1,3-positions. The white muscle triacylglycerol showed a much higher proportion of DHA in the 2-position than in the 1,3-positions. The skin triacylglycerol was relatively undifferentiated in respect to distribution of EPA and DHA. Saturated acids were least in the 2-position of the white muscle triacylglycerol and highest in the 1,3-position of the same fat. Not unexpectedly, the monoethylenic fatty acids of exogenous origin were located in the 1,3-positions and the highest level was in the dark muscle triacylglycerol. The distribution of the whole of the EPA and DHA is not dissimiliar from that projected from literature of fish triacylglycerols. It is concluded that benefits attributed to supplement of dietary mackerel, relative to herring, in certain types of hypertension follow from the total ω-3 fatty acid intake and not from any special distribution on glycerol of mackerel fatty acids.     

Composition of muscle tissue lipids of silver carp and bighead carp

Lipids have a complex role in the nutritional value of food. Some polyunsaturated fatty acids, characterized as essential, are extremely important for human health. This is primarily related to α-linolenic acid (18:3n-3), eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3). Content of polyunsaturated n-3 fatty acids is usually much higher in lipids of marine fish than in freshwater fish. Previous investigations have shown that muscle tissue of silver carp and bighead carp from fish farms may be a rich source of essential fatty acids. Because of that, the objective of this work was to examine contents and composition of fatty acids and total lipids in the muscle tissue of silver and bighead carp, with the aim to find out whether there are significant differences in this respect between the two species and to what extent the harvest season can influence the composition of lipids in these freshwater fish. This study showed that there is no significant difference either in the content of polyunsaturated n-3 and n-6 fatty acids, or in the n-6/n-3 fatty acid ratio in these two fish species. The lipids of both the silver and bighead carp from the spring harvest have significantly higher contents of the n-3 acids and a significantly lower n-6/n-3 ratio than fish from the autumn harvest.     

Effect of PUFA at sn‐2 position in dietary triacylglycerols on the fatty acid composition of adipose tissues in non‐ruminant farm animals

The influence of the distribution of polyunsaturated fatty acids on the glycerol backbone of dietary triacylglycerols on the fatty acid profile of adipose tissue and muscle phospholipids was investigated in growing‐finishing pigs (48) and broiler chicken (84). The animals were fattened on barley/soybean meal diets supplemented with a blend of soybean oil and beef tallow, either in the ratio 3:1 w/w (high‐PUFA) or 1:3 w/w (low‐ PUFA). Part of the high‐ and low‐PUFA blends was chemically interesterified to randomly distribute all fatty acids over the three positions of the glycerol. Thus, two sets of diets of identical overall fatty acid composition, but differing in the distribution of fatty acids in the triacylglycerols, were fed. Growth performance and carcass composition were neither affected by fatty acid composition nor by randomisation of dietary fats in either animal species. Apparent digestibility of energy was slightly lower in pigs fed the low‐PUFA blends. Fatty acid profile of subcutaneous fat of pigs and broilers as well as of internal body fat (lamina subserosa) and muscle phospholipids of pigs varied according to the dietary fatty acid composition but was not affected by randomisation of dietary fats. These findings are explained in terms of the hydrolysis of TAG during transport of lipids from enterocytes to adipose tissue cells and the continuous lipolysis and re‐esterification of fatty acids that take place in adipose tissue cells.