The incorporation of arachidonic acid (AA) as compared to eicosapentaenoic acid (EPA) into human platelet phospholipids was tested by incubating washed platelets with a known mixture of [3H]AA and [14C]EPA. Following incubation, the platelet lipids were extracted, the individual phospholipids--phosphatidylcholine (PC), phosphatidylserine (PS), phosphatidylinositol (PI) and phosphatidylethanolamine (PE)- were separated by thin layer chromatography, and their corresponding [3H]/[14C] ratios were determined. Based on a [3H]/[14C] ratio of unity for the substrate mixture, the PC, PS, PI and PE exhibited ratios of 0.55, 0.93, 1.12 and 0.74, respectively, which were significantly different from 1.00 in all instances except in the case of PS. These results indicate that PC and PE selectively incorporated EPA, while PI showed preference toward AA. These selectivities may account partly for the differing AA/EPA mass ratios that have been observed among the individual phospholipids of human subjects consuming fish oils.
