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The aim of the study was to determine the influence of conjugated isomers of linoleic acid (CLA) and/or selenium (Se) on the body mass gain of rats, feed intake, and the levels of CLA isomers and some other fatty acids in the femoral muscle. Rat diets enriched in Se, the trans-10,cis-12 isomer and mixtures of the CLA isomers (regardless Se supplementation) tended to decrease body mass gain compared with control rats, while simultaneously supplementation with Se and the trans-10,cis-12 isomer resulted in the highest increase. A mixture of CLA isomers and/or Se supplementation, and the trans-10,cis-12 isomer decreased feed intake, whereas the cis-9,trans-11 isomer, regardless of Se supplementation, only slightly influence of feed intake. Enriching diets with CLA isomers increased their level in muscles as well as the level of non-CLA isomers containing conjugated double bonds (CD). In rats receiving simultaneously Se and mixtures of the CLA isomers or individual CLA isomers the CLA isomers and CD levels in muscles were higher compared with rats fed only the CLA isomers. Rats fed individual isomers or their mixture showed minute changes in C8:0 and C10:0 concentrations in muscles, while the C12:0, C14:0, C16:0 and C18:0 contents were generally lower. A small increase in C10:0 and C16:0 content was found in rats fed the trans-10,cis-12 isomer. Supplementing Se to diets enriched in CLA isomers usually resulted in an increase in the saturated fatty acid content in muscles in comparison with rats fed only CLA isomers. The linoleic acid content in muscles was enhanced by the Se supplemented diets enriched in the trans-10,cis-12 isomer or in the 2% CLA isomer mixture, although 1% mixture of the CLA isomers or the cis-9,trans-11 isomer dosed simultaneously with Se also increased the level of linoleic acid, albeit insignificantly. The Se supplemented diet enriched 184 CLA IN MUSCLES OF RATS FED CLA ISOMERS AND SE in the trans-10,cis-12 isomer or 2% mixture of the CLA isomers produced the highest increase of γ-linolenic acid, the total fatty acid and polyunsaturated fatty acid content in rat muscle.

The effects of conjugated linoleic acid (CLA) isomers and/or selenium (as Na 2 SeO 4) on rat growth performance and levels of some fatty acids (FA) in femoral muscles and perigonadal fat were investigated. Feeding a mixture of CLA isomers, the trans-10,cis-12 isomer, or selenium (Se) tended to decrease the rats' body weight compared with the control animals, whereas a diet supplemented with both Se and the trans-10,cis-12 isomer produced the highest increase in body weight gain and the highest feed conversion efficiency. None of the experimental diets had any influence on brain, kidney, pancreas, or liver weight, while they significantly increased spleen mass. The administered CLA isomers significantly increased the contents of CLA isomers and non-CLA fatty acids containing conjugated double bonds (CD) in the assayed tissues. Se and individual CLA isomers or their mixture increased the CLA isomer and CD contents in muscles, while feeding only the cis-9, trans-11 isomer and Se resulted in an increase in CD and sum of all CLA isomers in fat. These results demonstrate that the trans-10,cis-12 isomer is preferentially driven through the β-oxidation pathway in muscles and fat compared with the cis-9,trans-11 isomer. CLA isomers added to Se-unsupplemented or-supplemented diets increased the levels of total FA in muscles only, while decreased the level of total assayed saturated FA in fat. Feeding Se and individual CLAs or a mixture of these isomers resulted in increasing both the sum of cis-monounsaturated FA (cis-MUFA), CD and polyunsaturated FA (PUFA) in muscles, but generally resulted in decreasing the level of total saturated FA, cis-MUFA and PUFA in fat. The interaction between Se and a mixture of CLA isomers or the trans-10,cis-12 isomer most effectively protected CLA isomers from peroxidation damage and/or catabolism in muscles.

The influence of dietary CLA isomer(s) and/or selenized yeast on the growth, concentration of CLA isomers and other fatty acids in the liver was investigated in rats. Plasma blood triacylglycerols (TAG), total cholesterol (TC), HDL and LDL cholesterol fractions in relation to dietary CLA isomer(s) and/or selenium (Se) were analysed. The experiment was performed on female rats (Wistar), 8 weeks of age and initial body weight of about 200 g. After a 1-week preliminary period, for 4 weeks the animals were fed a diet enriched in conjugated linoleic acid (CLA) isomer(s) and selenized yeast (2×2 experimental design). Dietary Se or/and CLA isomer(s) resulted in small changes in the spleen, heart, kidneys and brain, and increased liver weight. Administration of Se and trans10cis12CLA most efficiently increased the body weight gain of rats. CLA isomer(s) administered with or without Se elevated the CLA isomer(s) level in the liver. These results demonstrate that trans,transCLA isomers are metabolized more slowly, while cis,trans/trans,cisCLA isomers, more rapidly to longchain fatty acids containing a conjugated double bond. Enrichment of the diet in CLA isomer(s) with or without Se caused a reduction in the capacity of Δ9-, Δ6-and Δ5-desaturases in the liver, while dietary trans10cis12CLA or the CLA isomer mixture increased Δ4-desaturases. The contents of oleic acid, C20:4n-6, and C20:5n-3 decreased in the liver, whereas the level of C22:5n-3 and C22:6n-3 increased in the liver of rats fed the CLA isomer mixture. Individual dietary CLA isomers with or without Se increased the concentration of palmitic and stearic acids in the liver. All experimental diets increased the concentration of triacylglycerols in blood plasma, while trans10cis12CLA with or without Se usually decreased the concentration of total cholesterol, LDL, and HDL cholesterol.

In the current paper we describe the development of our method for quantification of underivatized individual conjugated linoleic acid (CLA) isomers by silver ion liquid chromatography (Ag +-HPLC). Positional and geometric CLA isomers were separated on two commercially available Chrompac (The Netherlands) ChromSpher 5 µm Lipids columns (250 x 4.6 mm) protected by a guard column (10 x 3 mm) containing the same stationary phase. Lyophilized skeletal muscle, adipose tissue, liver, brain and pancreas samples were hydrolyzed with 2M NaOH at 80-85 o C for 30-35 min in sealed tubes. After cooling, the hydrolyzates were acidified with 4M HCl and the free CLA isomers were extracted with dichloromethane. The organic solvent was removed in a stream of argon and then the residue was re-dissolved in dichloromethane followed by injection of the resulting solution (10-30 µl) onto the HPLC columns (column temperature: 25 o C). A mobile phase of 1.6% acetic acid and 0.0125% acetonitrile in n-hexane was chosen as the optimum mobile phase for fractionation of the individual CLA isomers. Analyses of underivatized isomers were performed by the isocratic elution program (flow-rate of 1 ml/min) and UV detection at 234 nm. All positional and geometric CLA isomers in standards and biological samples were efficiently retained on the columns and were satisfactorily separated from all endogenous species present in biological materials in about 55 min. The first low intensity peak group was trans-trans CLA isomers (23-27 min), the second highest intensity peak group was cis-trans/trans-cis isomers (31-38 min), while the last group was low intensity cis-cis isomers (41-52 min). The use of two silver ion-exchange columns with direct UV detection offers low limits of detection (0.14-1.02 ngl-1), quantification (0.42-3.06 ngl-1) and satisfactory "purity" of analytical peaks, so, this simple Ag +-HPLC method can be used for routine analysis of CLA isomer biodistribution in the body of animals.

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The aim of the study was to determine the influence of diets containing 1.5% conjugated linoleic acid isomers (CLAmix) and/or a high or low level of selenite (0.2 ppm Se ( L Se) or 0.5 ppm Se ( H Se)) on the body weight gain (BWG), feed conversion efficiency (FCE), and concentrations of CLA isomers and other fatty acids (FA) in the liver and femoral muscle of female rats fed ad libitum these experimental diets for 6 weeks. It was found that the diet containing the CLAmix and 0.5 ppm Se ( H Se) resulted in the highest increase in BWG and FCE compared with values for BWG and FCE of all other groups. This diet most efficiently increased the concentration of Se in the liver and muscles. The content of CLA isomers in muscles was ~20-fold higher than in the liver. There were usually no differences in the concentrations of c9t11CLA, t10c12CLA and the sum of CLA isomers in the liver and muscles of rats fed the diet with CLAmix with or without H Se, whereas these values in the liver and muscles were usually lower for rats fed the diet enriched in CLAmix and 0.2 ppm Se ( L Se) compared with those fed the diet with CLAmix. The diets enriched in CLAmix and/ or Se (as L Se or H Se) caused a decrease in the Δ9-desaturase index only in the liver. The current study shows that the highest values of the Δ4-, Δ5-and Δ6-desaturase indexes were in muscles of rats fed the diet enriched in CLAmix. This diet most efficiently increased the value of the Δ4-desaturase index in the liver, the desaturase responsible for the most efficient increase in the content of c4c7c10c13c16c19C22:6n-3 in the liver. Our study indicates that dietary CLAmix stimulated β-oxidation of FA in skeletal muscles, while promoting the accumulation of FA, particularly n-3 polyunsaturated fatty acids (PUFA), in the liver. The diet enriched in CLAmix and H Se assured satisfactory ratios of PUFA to saturated FA and PUFA to the sum of all assayed FA in the liver and Journal of Animal and Feed Sciences, 18, 2009, 564-

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