DIETARY-FAT ALTERS MEMBRANE-COMPOSITION IN ROD OUTER SEGMENTS IN NORMAL AND DIABETIC RATS - IMPACT ON CONTENT OF VERY-LONG-CHAIN (C-GREATER-THAN-OR-EQUAL-TO-24) POLYENOIC FATTY-ACIDS

The effect of high n-3 (5.8%, w/w) vs. a low n-3 (1.2%, w/w) fatty acids in a diet with a low ratio of polyunsaturated/saturated fatty acids (P/S = 0.27) content was investigated to determine the effect of diet on the level of long- and very-long-chain fatty acids (VLCFA C greater than or equal to 24) in phospholipids of rod outer segments (ROS) of normal and diabetic rats. After 6 weeks of feeding, diets high in n-3 fatty acids increased the levels of 22:5(n-3) and 22:6(n-3), while decreasing the 22:5(n-6) level in all major phospholipid classes. n-6 and n-3 VLCFA of C24 to C34 with 4, 5 and 6 double bonds were found only in phosphatidylcholine (PC) while other phospholipid classes contained only C24 fatty acids as minor components. The content of VLCFA in PC was approx. 6.7% (w/w) of total fatty acids in the ROS. Feeding a high n-3 fatty acid diet significantly reduced n-6 tetraenoic VLCFA in all phospholipids. In the diabetic state, the levels of n-6 tetraenes and pentaenes in individual phospholipids were different from control animals. This study demonstrates that the VLCFA content of photoreceptor cells reflects the dietary level of n-3 fatty acids fed. The unique polyenoic n-6 and n-3 VLCFA appear to be synthesized from shorter chain precursors which respond to altering the ratio of n-6/n-3 fatty acids fed.