THE TRANSFER OF DOCOSAHEXAENOIC ACID FROM THE YOLK TO THE TISSUES OF THE CHICK-EMBRYO

Changes in the amounts of the major fatty acids present in the lipids of the yolk complex and the embryo were delineated during embryogenesi s of the chicken, The rates of transfer of palmitic, oleic, linoleic, linolenic and arachidonic acids from the lipids of the yolk complex we re essentially identical. In contrast, docosahexaenoic acid (DHA) was preferentially transferred from the yolk complex at a rate which was s ignificantly higher than that exhibited by the other major fatty acids . The rates of accumulation of both arachidonic acid and DHA in the li pids of the whole embryo were significantly greater than the rates obs erved for the C-16 and C-18 fatty acids, particularly between days 12 and 16 of the 21-day embryonic period. Analysis of the fatty acid comp osition of plasma lipid throughout development indicated that the tria cylglycerol fraction contained relatively high proportions (up to appr ox. 14% w/w of total fatty acids) of DHA, but much lower proportions ( approx. 3%) of arachidonic acid. In contrast, plasma phospholipid was enriched in arachidonic acid (up to approx. 18%), but contained much l ower proportions (generally less than 3%) of DHA. A considerable amoun t of DHA was incorporated into adipose tissue triacylglycerol, so that by the time of hatching, the tissue represented a major store of this fatty acid. Over the hatching period, the amount of DHA in adipose tr iacylglycerol decreased dramatically, by up to 85%, whereas there was little or no change in the amounts of the other major fatty acyl compo nents in this tissue. The amount of DHA as a component of brain phosph olipid increased continuously throughout the developmental period stud ied. However, by the time of hatching, the amount of DHA in brain phos pholipid represented less than 10% of the amount of this fatty acid or iginally present in the lipids of the yolk.