FATTY-ACID COMPOSITION OF PHOSPHOLIPIDS FROM CHICK NEURAL RETINA DURING DEVELOPMENT

The fatty acid composition of retina phospholipids from developing chicks was investigated to determine what changes, if any, occur in the relative levels of polyunsaturated fatty acids. Embryonic chicks were killed at 3-day intervals from day 6 through hatching (day 21), and at 1 week post-hatch. Fatty acids† † Fatty acids are specified by the number of carbons separated by a colon from the number of double bonds. The 'n-' designation indicates the number of carbons from the methyl end of the acyl chain to the nearest double bond. were prepared from retina phospholipids and were analysed by capillary gas-liquid chromatography. A comparison of the composition of yolk taken on day 6 with retinas isolated on that day revealed a much greater proportion of polyunsaturated fatty acids in the latter, suggesting an ability of the embryo to metabolize selectively unsaturated fatty acids at this early stage of development. Throughout the time course studied, saturated fatty acids constituted 50% of all fatty acids, most of which was due to palmitic acid (16:0; 33-41%). Among other saturated fatty acids, myristic acid (14:0) increased to maximal levels by day 18, then declined, while stearic acid (18:0) was minimal on day 12 and then increased. Polyunsaturated fatty acids varied between 14 and 23% of total fatty acids, depending on the developmental stage. One of the most remarkable changes in polyunsaturated fatty acids occurred in the levels of 22:4 (n-6). The proportion of this single fatty acid decreased from 9·4 to 2·4% between days 15 and 18. Relative levels of 22:5 (n-6) increased significantly between day 21 and 1 week post-hatch, from 1·1 to 3·2%. In this same time period, the proportion of 22:6 (n-3), the fatty acid known to be prominent in the outer segments of rod-dominant retinas, did not change. However, 22:6 (n-3) increased significantly from 3·8 to 9·5% between days 15 and 21, when outer segments are being formed. The fatty acid profile thus changes during development, and can be correlated with morphological stages of differentiation. The data also imply a relative enrichment of 22:6 (n-3) in the outer segment of this conedominant retina. © 1992.