The principal objective of this study is to elucidate metabolic functions of polyunsaturated fatty acids and phospholipids in nervous tissues with particular reference to their modulation by ethanol. Our studies focused on the oxygenation, release, incorporation and remodeling of the major polyunsaturates in the brain, docosahexaenoic acid (22:6n3) and arachidonic acid (20:4n6). We found that the major free fatty acid in brain was 20:4n6 and that chronic ethanol exposure increased the free 20:4n6 level in he brain considerably. Endogenous PLA2 activity, which hydrolyzed 20:4n6 preferentially, was found in the brain mitochondria and synaptosomes. On the contrary, cobra venom PLA2 hydrolyzed 22:6n3 faster than 20:4n6 in vitro from mixed liposomes or synaptosome preparations. We did not find any selective reincorporation of these fatty acids into synaptosomal lipids, indicating that the substrate specificity of the cobra venom PLA2 is different from that of the rat brain PLA2. In continuation of the study on characterization of pineal lipoxygenation, we found that 18 carbon fatty acids were also well-metabolized by the rat pineal primarily to 13-hydroxy derivatives. Platelets metabolized both substrates to 13- and 9-hydroxy compounds and leukocytes metabolized 18:2n6 to both 9- and 13-, and 18:3n3 to 9-, 12-, 13- and 16-hydroxy derivatives, respectively. These results indicated that the property of 15-LO in pineal differs from that of leukocytes or platelets. In order to understand the enrichment process of the major polyunsaturated fatty acids in brain, incorporation of 20:6n3 and 20:4n6 from diet underwent the chain shortening and elongation processes before incorporation into the brain. This oxidation was especially active for 22:6n3 and during the first week after birth.
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