OXIDATIVE-METABOLISM OF [1-C-14] MONO-TRANS ISOMERS OF LINOLEIC AND ALPHA-LINOLENIC ACIDS IN THE RAT

Trans polyunsaturated fatty acids are formed during processing of vege table oils such as deodorization and frying. The oxidative metabolism of linoleic and cr-linolenic acids and of their mono-trans isomers (9 cis,12 trans-18:2, 9 trans,12 cis-18:2 and 9 cis,12 cis,15 trans-18:3, 9 trans,12 cis,15 cis-18:3, respectively) was studied in fasting rats . A single dose of 18.5 MBq of each [l-C-14] labelled fatty acid (260 mu g) was orally given to the animals. The (CO2)-C-14, expired was mon itored during 24h. Radioactive countings of the CO2-trapping agent wer e performed at regular intervals up to 24h after oral administration o f the radiolabelled fatty acid. Radioactive countings were also perfor med on several tissues (liver, heart, brain, kidneys, sus-epidydimal f at, gastrocnemian muscle, gastrointestinal tract and carcass). The (CO 2)-C-14 production 24h after oral administration of the fatty acid ran ged from 55.5% to 68.7% of the radioactivity administered for the C18: 2 isomers and from 69.7% to 73.5% for the C18:3 fatty acids. From 6 to 24 h, (CO2)-C-14 recovery was significantly higher after oral adminis tration of 9 cis,12 trans-18:2 than after giving both other octadecadi enoic isomers. C-14 retention per gram of tissue in the liver and in t he heart was significantly lower after feeding 9 cis,12 trans-ls:2 tha n after administration of both other C18:2 isomers. C-14 retention per gram of tissue in the muscle was significantly lower after administra tion of both trans C18:2 isomers compared to linoleic acid. Neither (C O2)-C-14 recoveries nor C-14 retentions were significantly different a fter administration of the three octadecatrienoic acids. The differenc e observed in (CO2)-C-14 recovery within the dienes was probably not d ue to a higher specificity of the enzymes involved in the beta-oxidati on sequence for the Delta 12 trans double bond, as previously reported . Indeed, due to the labelling of the fatty acids on the carboxyl end, C-14 values recorded in the CO2-trapping agent were only due to the f irst cycle of beta-oxidation. (C) 1998 Elsevier Science B.V.