Metabolism of Adrenic and Arachidonic Acids in Nervous System Phospholipids

Abstract

High concentrations of polyunsaturated fatty acids of the (n-6) and (n-3) series are found in the glycerophospholipids of the nervous system. The most plentiful are docosahexaenoic acid, 22:6 n-3, adrenic acid, 22:4 n-6, and arachidonic acid, 20:4 n-6. These fatty acids are distributed very differently in different glycerophospholipids (Tables 1 and 2). Generally, the ethanolamine lipids have higher proportions of the polyunsaturated fatty acids and lower proportion of the saturated fatty acid, palmitic acid. The comparison of human myelin with mouse brain compositions shows lower proportions of saturated and 22:6 fatty acids in myelin and higher proportions of monounsaturated fatty acids, mostly in oleic acid, 18:1. In human myelin the principal phospholipid is ethanolamine plasmalogen. This phospholipid contains about twice as much adrenic acid as arachidonic acid. The contents of these two fatty acids are about equal in the phosphatidylethanolamine. The mouse brain has lower proportions of adrenic acid than does the human brain. The proportion of adrenic acid in mouse brain ethanolamine glycerophospholipids is particularly important in the ether-linked types, ethanolamine plasmalogen and the alkylacyl type of ethanolamine glycerophospholipid (Fig. 1). In contrast, in the choline glycerophospholipids of mouse brain adrenic acid is almost completely missing whereas some arachidonic acid is present.