FATTY-ACID RELEASE IN INCUBATIONS OF SERUM WITH SYNAPTOSOME AND MYELIN SUBFRACTIONS OF BRAIN

To study lipid breakdown in brain membranes following hemorrhage, synaptosome and myelin fractions isolated from rat brain were incubated with rat serum. After 3 h in vitro at 37°C, 0.43 and 0.26 μmol of fatty acid were released in incubations containing synaptosomes (1.37 μmol phospholipid) or myelin (1.23 μmol phospholipid), respectively, in the presence of 0.25 mL serum. Less than 0.05 μmol of fatty acid was liberated in incubations containing only serum, synaptosomes, or myelin. For synaptosomes and serum, docosahexaenoate was the principal fatty acid released (28 mol% of total) after 3 h of incubation. This fatty acid and arachidonate made up 43 mol% of the liberated fatty acid. The presence of free docosahexaenoate was of interest, as this fatty acid is particularly enriched in phosphatidylserine and phosphatidylethanolamine, phospholipids found in the cytoplasmic half of the synaptosomal plasma membrane and in interior synaptosomal membranes. In incubations of serum and myelin, oleate was the major free fatty acid produced in 30 min to 3 h of incubation (29-35 mol% of total). After 3 h, docosahexaenoate contributed 20 mol% to the total. The release of fatty acids from the membranes may be mediated by serum phospholipase(s) or possibly by activated endogenous lipolytic activities.