Geometry of conjugated double bonds of CLA isomers in a commercial mixtureand in their hepatic 20 : 4 metabolites

Rats were fed a fat-free diet for 2 wk. After this period, while maintainin g the animals on the same diet, the rats were given intragastrically 180 mg per day of a mixture of conjugated linoleic acids (CLA) as triacylglycerol s. Gas chromatography-mass spectrometry (CC-MS) analyses of this mixture, a s well as hydrazine reduction and GC-MS and GC-Fourer transform infrared an alyses of the resulting monoenes, revealed the presence of two major isomer s, the 9c,11t- and the 10t,12c-18:2 accompanied by smaller amounts of the 8 t,10c and the 11c,13t-18:2 isomers. Minor quantities of cis,cis and trans,t rans conjugated isomers also were detected. The total fatty acid methyl est ers from the liver lipids were fractionated by reversed-phase high-performa nce liquid chromatography, and the fraction containing the 20:4 isomers was further fractionated by silver nitrate thin-layer chromatography. A band c ontaining two 20:4 conjugated isomers was submitted to hydrazine reduction and the resulting monoenes analyzed by GC-MS as dimethyl-oxazoline derivati ves. The two conjugated isomers were tentatively identified as 5c,8c,11c,13 t-20:4 and 5c,8c,12t,14c-20:4. These could be formed by desaturation and el ongation of the 9c,11t- and 10t,12c-18:2 present in the commercial CLA mixt ure.