IN VIVO METABOLlSM OF LABELED OLEIC AND LINOLEIC ACIDS BY THE

Radioactive oleic and linoleic..: adds, labeled with 3II'in the ehain and 14C in the carbonyl group, were administered to white ll~ghorn laying hens. Mixture~ fed in separate experiments included: (1) 3H-.and 14C-Iu.iJeled oleic acid, (2) 311_ and 14C-Iabeled linoleic..: acid and (3) eH] oleic acid and r14Cllinoleic acid. The 3H/ 14C ratios of both the neutral lipid and phospholipid fractions from the egg yolk and of the isolated acids from these lipid fractions were compared to that in the administered mixture. Agreement in the 3H/14C ratios for the neutral lipid fraction from each of the feeding f'xperiments indicated that neither thl" 'II_ and 14e labeled acids nor the oleic or linoleic acids wprp <1istinguishable during synthesis of the neutrallipi<1. Analysis of the phospholipid fradions showed that when dual-labeled mixtures of oleic acid were administered, 3ure ratios were elevated an<1, therefore, there was selective elimination of the 14C label. When duai-labele<1 mixtures of linoleic acid were administered, the 3H/ 14 C ratios were in agreement; and when the two acids were administered simultaneously as a dual-labeled mixture, there was selective incorporation of linoleic acid. These findings indicate separate metabolic pathways for synthesis of neutral lipid and phospholipid in c;,;g yolk as expecte<1, as well as preferential use of Lhe essential fatty acid in the phospholipid by the hen.