Effect of low levels of dietary fish oil on fatty acid desaturation and tissue fatty acids in obese and lean rats

Abstract

The effect of very low levels of dietary long-chain n-3 fatty acids on delta 6 desaturation of linoleic acid (18:2n-6) and alpha-linolenic acid (18:3n-3), and on delta 5 desaturation of dihomo-gamma-linolenic acid (20:3n-6), in liver microsomes and its influence on tissue fatty acids were examined in obese and lean Zucker rats and in Wistar rats. Animals fed for 12 wk a balanced diet containing ca. 200 mg of long-chain polyunsaturated n-3 fatty acids per 100 g of diet were compared to those fed the same amount of alpha-linolenic acid. Low amounts of long-chain n-3 fatty acids greatly inhibited delta 6 desaturation of 18:2n-6 and delta 5 desaturation of 20:3n-6, while delta 6 desaturation of 18:3n-3 was not inhibited in Zucker rats and was even stimulated in Wistar rats. Inhibition of the biosynthesis of long-chain n-6 fatty acids was reflected in a decrease in arachidonic acid (20:4n-6) content of serum lipids when fasting, and also in the phospholipid fatty acids of liver microsomes. On the contrary, heart and kidney phospholipids did not develop any decrease in 20:4n-6 during fish oil ingestion. Docosahexaenoic acid (22:6n-3), present in the dietary fish oil, was increased in serum lipids and in liver microsome, heart, and kidney phospholipids.