The incorporation of orally fed radioactive gamma-linolenic acid and linoleic acid into the liver and brain lipids of suckling rats.

The incorporation of radioactivity from orally administered gamma-linolenic acid-1--14C and linoleic acid--3H into the liver, plasma, and brain lipids of suckling rats was studied. Significantly more radioactivity from the former compound was incorporated into the liver and brain lipids 22 hr after dosing. The distribution of the radioactivity in the fatty acids of the liver and brain lipids was different for each isotope. Most of the -3H was still associated with linoeic acid, whereas most of the -14C was in the 20:3 and 20:4omega6 fractions. These results suggest that the desaturation of linoleic to gamma-linolenic acid in vivo is a rate-limiting step in the conversion of linoleic to arachidonic acid.