EFFECTS OF TRANS N-6 FATTY-ACIDS ON THE FATTY-ACID PROFILE OF TISSUESAND LIVER MICROSOMAL DESATURATION IN THE RAT

18:2 Delta 9c,12t and 18:2 Delta 9t,12c are present in our diet, as re sult of heat treatment of vegetable oils. A nutritional study was carr ied out in order to obtain more precise information on the conversion of these two isomers into long chain polyunsaturated fatty acids (PUFA ) by rat tissues. This in vivo study performed using rat fed with smal l quantities of mono trans linoleic acid isomers (0.6% of total energy ) showed that 18:2 Delta 9c,12t was converted into 20:4 Delta 5c,8c,11 c,14t while 18.2 Delta 9t,12c was only slightly converted into 20:4 De lta 5c,8c,11t,14c. Furthermore 18:2 Delta 9t,12c was preferentially el ongated into 20:2 Delta 11t,14c, Each C20 metabolite of these mono tra ns 18:2 isomers was isolated as methyl ester by semi-preparative high- performance liquid chromatography (HPLC) followed by silver nitrate th in layer chromatography (AgNO3-TLC). The structure of the components w as identified using partial hydrazine reduction, AgNO3-TLC of the resu lting monoenes and gas-liquid chromatography coupled with mass spectro metry (CC-MS) of the 4,4-dimethyloxazoline (DMOX) derivatives. Fourier -transform-infrared spectroscopy (GC-FTIR) confirmed the trans geometr y. Gas-liquid chromatography (GC) analyses showed that 18:2 Delta 9c,1 2t and 18:2 Delta 9t,12c were present in different tissue lipids (live r, heart, testes, brain and adipose tissue), and without any modificat ion in the amount of 20:4n-6. 20:4 Delta 5c,8c,11c,14t was incorporate d in different rat tissues except in brain. Furthermore, its incorpora tion followed that of its structural analogue, 20:3n-9 in liver phosph olipid classes (phosphatidylethanolamine, phosphatidylinositol and pho sphatidylcholine). Finally, an in vitro study carried out with rat liv er microsomes showed that dietary trans 18:2 isomers could inhibit the Delta 6-desaturation of 18:2n-6 to 18:3n-6 and the Delta 5-desaturati on of 20:3n-6 to 20:4n-6.