BRAIN ARACHIDONIC-ACID INCORPORATION AND PRECURSOR POOL SPECIFIC ACTIVITY DURING INTRAVENOUS-INFUSION OF UNESTERIFIED [H-3] ARACHIDONATE INTHE ANESTHETIZED RAT

Brain fatty acid incorporation into phospholipids can be measured in v ivo following intravenous injection of fatty acid tracer. However, to calculate a cerebral incorporation rate, knowledge is required of trac er specific activity in the final brain precursor pool. To determine t his for one tracer, unesterified [H-3]arachidonate was infused intrave nously in pentobarbital-anesthetized rats to maintain constant plasma specific activity for 1-10 min. At the end of infusion, animals were k illed by microwave irradiation and analyzed for tracer specific activi ty and concentration in brain phospholipid, neutral lipid, and lipid p recursor, i.e., unesterified arachidonate and arachidonoyl-CoA, pools. Tracer specific activity in brain unesterified arachidonate and arach idonoyl-CoA rose quickly (t(1/2)<1 min) to steady-state values that av eraged <5% of plasma specific activity. Incorporation was rapid, as >8 5% of brain tracer was present in phospholipids at 1 min of infusion. The results demonstrate that unesterified arachidonate is rapidly take n up and incorporated in brain but that brain phospholipid precursor p ools fail to equilibrate with plasma in short experiments. Low brain p recursor specific activity may result from (a) dilution of label with unlabeled arachidonate from alternate sources or (b) precursor pool co mpartmentalization. The results suggest that arachidonate turnover in brain phospholipids is more rapid than previously assumed.