EFFECT OF DIETARY N-3 AND N-6 FATTY-ACIDS ON FATTY-ACID DESATURATION IN RAT-LIVER

To study the effect of high-fat diets with varying contents of n - 3 and n - 6 fatty acids on the metabolism of essential fatty acids, the rat liver microsomal fatty acid desaturases were measured. The rats were fed for 3 weeks with diets high in linseed oil (18:3(n - 3)), sunflower seed oil (18:2(n - 6)) or fish oil (20:5(n - 3) and 22:6(n - 3)) (20%, w/w) using pellet fed rats as a reference. The DELTA-6-desaturase using 18:2(n - 6) or 18:3(n - 3) as substrates was stimulated 1.5-2.5-fold by linseed or sunflower seed oil, compared to the pellet reference. The DELTA-5-desaturase was stimulated 3.5-fold with linseed oil and 2.5-fold with sunflower seed oil, while the DELTA-9-desaturase was inhibited by all the high-fat diets. The DELTA-6-, 5- and 9-desaturase activities were in all cases considerably reduced with fish oil as compared to linseed and sunflower seed oil diets. With pellet fed rats the rates were highest for DELTA-9-desaturation and in decreasing order lower for DELTA-5-desaturation, DELTA-6-desaturation with 18:3 (n - 3) as substrate and finally DELTA-6-Desaturation with 18:2(n - 6) as substrate. The content of 20:4(n - 6) in liver phospholipids increased with the diets rich in 18:2(n - 6), and was reduced for the fish oil diet enriched in 20:5 and 22:6(n - 3) fatty acids. The amount of 20:5(n - 3) in phospholipids was as high with linseed oil diet as with the fish oil diet, while the 22:6(n - 3) content was only increased with the fish oil diet.