Metabolism of linoleate versus linoelaidate in the laying hen

The metabolic fate in the laying hen of linolaidic acid, the trans,trans-geometric isomer of linoleic acid, was compared to that of the naturally occurring cis,cis linoleate. In two experiments, mixtures of radioisotope-labeled linoleate and linoelaidate were orally administered to a set of three laying hens. A third mixture consisting of linoleate-3H and linoleate-14C was fed to three hens to measure biological isotope effects. Isotopic ratios (3H/14C) of the neutral lipid and phospholipid fractions isolated from egg yolks and of the octadecadienoic acids from these fractions were compared to those of the administered mixtures. The 3H/14C ratios indicate that linoelaidic acid and linoleic acid are equally incorporated into egg yolk neutral lipids and phospholipids. Arachidonic acid was found exclusively in the phospholipid fraction and was radiolabeled with the isotope from the cis,cis octadecadienoate isomer only. Further detailed analysis of individual neutral lipid components indicated: (a) discrimination against the trans,trans isomer in cholesteryl esters and (b) no discrimination against either isomer in triacylglycerols.