The principal objective of this subject is to elucidate metabolic functions of polyunsaturated fatty acids an phospholipids in nervous tissues with particular reference to their modulation by ethanol. Our studies focused on the major polyunsaturates in the brain, docosahexaenoic acid (22:6n3) and arachidonic acid (20:4n6). The oxygenation, release and incorporation of these polyunsaturates into various lipid classes was studied. Since we have previously observed that lipoxygenation occurs only in the pineal, the present study focused upon characterization of pineal lipoxygenation. Both 12- and 15-LO activity was found for 20:4n6 and 22:6n3. The endogenous production of these LO products were also observed with a higher ratio of 15-LO to 12-LO products in comparison to in vitro production from exogenous substrates. Both 12- and 15-LO activity was recovered mainly in the microsomal plus cytosolic fraction. In addition to mono-hydroxy derivatives, low and variable levels of epoxy, hydroxy- derivatives were formed from both 20:4n6 and 22:6n3 by the pineal. They were 10-hydroxy 11, 12-epoxy-20:3n6 and 12-hydroxy-3, 14-epoxy-22:5n3, respectively. We found that the major polyunsaturated free fatty acid in brain was 20:4n6 . We also found that chronic ethanol exposure increased the free 20:4n6 level in the brain considerably with a concomitant decrease in the vitamin E level. Certain subcellular fractions such as myelin or mitochondria and the lipid fraction associated with protein showed slight losses of polyunsaturates. In vitro analysis using cobra venom PLA2 indicated that hydrolysis of 22:6n3 was faster than 20:4n6. This observation indicates a high degree of structural recognition in the PLA2 hydrolysis, however, this was not consistent with the finding that 20:4n6 ws the major free fatty acid found in the brain. The discrepancy may be due to the different characteristics of brain and cobra venom PLA2 enzymes, but the possibility of selective reincorporation of 22:6n3 in brain cannot be excluded. However, the incorporation profiles of 20:4n6 or 22:6n3 injected separately into the lateral ventricle of the rat brain did not indicate differences in the efficiency of incorporation.
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