Competitive incorporation of dietary .OMEGA.-3 and .OMEGA.-6 polyunsaturated fatty acids into the tissue phospholipids in rats.

The incorporation of dietary omega-3 and omega-6 polyunsaturated fatty acids into the phospholipids of the liver, plasma and heart was studied by feeding rats with diets of increasing amounts of fish oil and/or corn oil up to 5% each for 2 weeks. Irrespective of the sources and amounts of dietary fat, total unsaturated fatty acids were 53-60% of phospholipid fatty acids in liver and plasma, and were 70-73% in heart. In all the animals either given or not given unsaturated fatty acid in diet, the sums of polyunsaturated fatty acids with more than three double bonds such as arachidonic acid, omega-3 polyunsaturated fatty acids and endogenous omega-9 eicosatrienoic acid were always 31-35, 18-20 and 30-38% in liver, plasma and heart, respectively. Dietary omega-3 unsaturated fatty acids and arachidonic acid appeared to be comparably incorporated into the phospholipids and substituted for each other in the phospholipids. These data may suggest that omega-3 polyunsaturated fatty acids compete with arachidonic acid for the C-2 position of the phospholipids.