Interrelationship between dietary trans Fatty acids and the 6- and 9-desaturases in the rat.

Studies are reported on the effects of dietary trans fatty acids on the 6- and 9-acyl desaturase activities in the liver microsomes of rats fed essential fatty acid (EFA)-deficient and non-EFA-deficient diets. In experiment I, weanling male rats were fed a semisynthetic diet with either 10% safflower oil (SAF) or 10% hydrogenated coconut oil (HCO). At the age of one year, half of the dietary fat was replaced by a supplement containing elaidate, linolelaidate and cis, trans-trans,cis-18:2 (TRANS) for 12 weeks. In experiment II, male rats which were kept from weaning on a 10% (SAF + TRANS, or 5% HCO + 5% TRANS. Feeding TRANS depressed the 6-desaturase activity in the liver microsomes, especially in the EFA-deficient rats (HCO + TRANS group of experiment I). Unlike the 6-deaturase activity, the 9-desaturase activity was not inhibited by the dietary trans fatty acids and was significantly stimulated in the non-EFA-deficient rats (SAF + TRANS group of experiment I and HCO + TRANS groups of experiment II). This was evidence by incubation reaction and by comparisons of fatty acid consumptions and microsomal fatty acid levels, showing extra biosynthesis of 16:1 and 18:1 when TRANS was fed. The biosynthesis of essential (n-6) fatty acids was depressed by the TRANS supplement in EFA-deficient as well as in non-EFA-deficient animals.