Effects of a fatty acid deficiency on lipids of whole brain, microsomes, and myelin in the rat

The lipid compositions of whole brain homogenates and microsomal and myelin fractions isolated from the brains of 6-month-old rats raised on a lab chow diet, a fatty aciddeficient diet, and a deficient diet supplemented with 595 (w/w) corn oil were determined. Brain and body weights were significantly lower in the fatty acid-deficient group. The compositions of alk-1-enyl groups and phospholipids of whole brain homogenates of rats maintained on the three diets were not different. However, marked alterations were found in the acyl group compositions of the major phosphoglycerides from whole brain homogenates and from the myelin and microsomal fractions of rats maintained on the fatty acid-deficient diet. With the deficient diet, 20:3(n 9) was found in the major phosphoglycerides as well as in the myelin and microsomal fractions. In addition, the levels of 20:4(n 6) and 22:4(n 6) were decreased. The levels of 20:4(n 6), 22:4(n 6), and 22:5(n 6) were higher in the brain phosphoglycerides of rats maintained on the corn oil-supplemented diet than on the lab chow control diet, and the elevation in these acyl groups was more evident in the microsomal fraction than in Supplementary groups the myelin fraction. key words phosphoglycerides . acyl the chemical composition of the brain is known to be relatively constant after maturity and is more resistant to the influences of external factors than are other organs, the brain may be vulnerable to protein Presented in part at the 54th Annual Meeting of the Federation of American Societies for Experimental Biology, Atlantic City, N.J., 1970. Abbreviations: CPG, choline phosphoglycerides; EPG, ethanolamine phosphoglycerides; GPE, sn-glycero-3-phosphorylethanolamine; SPG, serine phosphoglycerides; IPG, inositol phosphoglycerides; TLC, thin-layer chromatography ; GLC, gas-liquid chromatography. Fatty acid designations, number of carbon atoms: number of double bonds. undernutrition and other dietary deficiencies imposed during early periods of growth and development (1-3). Recent experimental findings showed that the fatty acid composition of the developing brain can be altered by variation of the dietary fatty acid levels, especially the essential fatty acids (3-8). Any alteration of brain fatty acids may also affect brain metabolism, since fatty acids are important molecular components of the subcellular membranes. Examples of a diet-related alteration of mitochondrial functions have been demonstrated in the liver (9-1 2). Recently, Clausen and MZller (13) showed that rats reared on a polyunsaturated fatty acid-deficient diet were more susceptible to experimental allergic encephalomyelitis (EAE) than control rats reared on a normal diet. This fact as well as the other results cited may be taken as evidence of a diet-induced change in the chemical structure of cerebral membranes. Since dietinduced changes in the composition of rat brain membranes may not be as evident in studies of whole brain homogenate as in subcellular fractions, it seemed appropriate to study acyl group composition of isolated myelin and microsonial fractions in addition to whole brain honiogenates of rats maintained on various deficient diets. The chief aim of the present study was to compare the lipid and acyl group compositions of whole brain homogenate and microsomal and myelin fractions isolated from the brains of rats fed a lab chow diet, a fatty acid-deficient diet, and a fatty acid-supple-