Influence of diet on conversion of 14C1-linolenic acid to docosahexaenoic acid in the rat.

14C1-Linolenic acid was incorporated into lipids of hearts, livers, and carcasses of male rats. We studied the influence of diet composition on extent and distribution of radioactivity. A CHOW diet, a purified, essential fatty acid (EFA)-deficient diet, a purified control diet, and EFA-deficient diets with four fatty acid supplements were used. Supplements of 18:2n-6, 20:4n-6, 15:3n-3, and 22:6n-3 were given as single doses. Radioactivities in liver phosphatidyl ethanolamines (PE), phosphatidyl cholines, and neutral lipids were measured. The distribution of radioactivity among the fatty acids in liver phospholipids was determined. Rats on CHOW diet incorporated far less radioactivity than any other group into lipids of hearts and livers. Most of the activity in livers was recovered as 20:5n-3 and 22:6n-3 in all rats. In EFA-deficient rats, the radioactivity in 22:6n-3 of liver PE was still increasing 36 hr after 14C1-linolenic acid had been administered. The n-6 supplements (18:2n-6 and 20:4n-6) seemed to reduce the coversion of 20:4n-3 to 20:5n-3 (desaturation), whereas the n-3 supplements (18:3n-3 and 22:6n-3) reduced the conversion of 20:5n-3 to 22:5n-3 (elongation). Formation of 22:6n-3 may be controlled by 22:6n-3 itself at the elongation of 20:5n-3 to 22:5n-3.