The principal objective of this study is to elucidate metabolic functions of polyunsaturated fatty acids, docosahexaenoic acid (22:6n3) and arachidonic acid (20:4n6) in astroglial cells and nervous tissues with particular reference to their modulation by ethanol. Ethanol selectively and significantly decreased the accumulation of both 22:6n3 and 20:4n6 in PS in C-6 glioma cells without changing the total incorporation of these fatty acids considerably, after treatment with 25 mM ethanol for 3 weeks. Concomitantly, inhibition of serine incorporation was observed. These data indicate that the phospholipid remodeling process, especially the serine exchange reaction, is impaired by chronic ethanol exposure. We have previously demonstrated that both 20:4n6 and 22:6n3 were readily hydrolyzed from C-6 glioma cells under both stimulated and unstimulated conditions. During this period, we found that stimulation of serotonin (5-HT) receptors is coupled to the release of both 20:4n6 and 22:6n3. Pharmacological and biochemical characterization using specific agonists, antagonists and inhibitors indicated that 5-HT2A receptor and phospholipase A2 were involved in the mobilization process. The observed release of 20:4n6 and 22:6n3 may represent another signaling mechanism of the 5-HT2-like receptors in cells of astroglial origin. Exposure of C-6 glioma cells to 20 mM ethanol for as little as 2 weeks resulted in a significant decrease in this receptor-mediated mobilization without significantly altering the ionophore-stimulated release, indicating that ethanol affected the receptor-agonist or receptor-G protein coupling process rather than PLA2 activity. The altered regulation of receptor-mediated release of both fatty acids by ethanol in astroglia may play an important role in some of the physiological responses to ethanol. The metabolism of free polyunsaturated fatty acids by lipoxygenation has been implied to have biological significance. We found that in pineal, the only part of the brain where lipoxygenation occurs, the level of lipoxygenase products followed circadian rhythm with off-phase to that of melatonin, suggesting a close interrelationship of the lipoxygenation and melatonin synthesis in pineal. Exposure to ethanol for 24 days increased the daytime lipoxygenation significantly without major alteration of the lipid composition in pineal. The effect of the altered lipoxygenation on the melatonin synthesis is currently under investigation.
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