IDENTIFICATION OF 2 MOLECULAR-SPECIES OF RAT-BRAIN PHOSPHATIDYLCHOLINE THAT RAPIDLY INCORPORATE AND TURN-OVER ARACHIDONIC-ACID IN-VIVO

In vivo rates of arachidonic acid incorporation and turnover were dete rmined for molecular species of rat brain phosphatidylcholine (PtdCho) and phosphatidylinositol (PtdIns). [H-3]Arachidonic acid was infused intravenously in pentobarbital-anesthetized rats at a programmed rate to maintain constant plasma specific activity for 2-10 min. At the end of infusion, animals were killed by microwave irradiation, and brain phospholipids were isolated, converted to diacylglycerobenzoates, and resolved as molecular species by reversed-phase HPLC. Most [H-3]arachi donate (>87%) was incorporated into PtdCho and PtdIns, with arachidoni c acid at the sn-2 position and with oleic acid (18:1), palmitic acid (16:0), or stearic acid (18:0) at the sn-1 position. However, 10-15% o f labeled brain PtdCho eluted in a small peak containing two molecular species with arachidonic acid at the sn-2 position and palmitoleic ac id (16:1) or linoleic acid (18:2) at the sn-1 position. Analysis demon strated that tracer was present in both the 16:1-20:4 and 18:2-20:4 Pt dCho species at specific activities 10-40 times that of the other phos pholipids. Based on the measured mass of arachidonate in each phosphol ipid molecular species, half-lives were calculated for arachidonate of <10 min in 16:1-20:4 and 18:2-20:4 PtdCho and 1-3 h in 16:0-20:4, 18: 0-20:4, and 18:1-20:4 PtdCho and PtdIns. The very short half-lives for arachidonate in the 16:1-20:4 and 18:2-20:4 PtdCho molecular species suggest important roles for these molecules in brain phospholipid meta bolism and signal transduction.