Linoleic acid-induced fatty acid changes in platelet and aorta of the rat: effect of age and cholesterol.

The influence of age and cholesterol on polyunsaturated fatty acids (PUFA) levels was studied in young and old male Sprague-Dawley rats. Animals were fed a fat-free diet supplemented with 10% (by wt) safflower oil with or without 1% cholesterol for 8 wk. As a result of cholesterol feeding, proportions of linoleic acid (18:2n-6) and dihomo-gamma-linolenic acid (20:3n-6) were increased and that of arachidonic acid (20:4n-6) was decreased in the liver and platelet phospholipids in 64-wk-old rats, suggesting inhibitory effects of cholesterol on 20:4n-6 synthesis from 18:2n-6. The prominent age-dependent effect on the levels of PUFA was a retention of C-22 n-3 PUFA, accompanied by decreased C-22 n-6 PUFA and increased 20:3n-6 in the liver and platelet phospholipids. Ratio of 20:3n-6/20:4n-6 increased in 64-wk-old rats regardless of dietary cholesterol, suggesting depressed delta 5-desaturase with age. In aorta phospholipids, 20:3n-6 content and 20:3n-6/20:4n-6 ratio increased with cholesterol supplementation, but not with age. These results suggest that changes of PUFA composition of platelet phospholipids with age are closely linked with changes in liver phospholipids. The 20:4n-6 content in both platelet and aorta phospholipids is kept constant, despite other n-6 and n-3 PUFA being affected by age.