DIETARY ARACHIDONIC-ACID AND HEPATIC DESATURATION OF FATTY-ACIDS IN OBESE ZUCKER RATS

The effect of low levels of dietary arachidonic acid (20:4n-6) on Delt a 6 desaturation of linoleic acid (18:2n-6) and alpha-linolenic acid ( 18:3n-3), and on Delta 5 desaturation of dihomo-gamma-linolenic acid ( 20:3n-6) were studied in liver microsomes of obese Zucker rats, in com parison with their lean littermates. Fatty acid composition of serum t otal lipids and of phospholipids from liver microsomes and from total heart and kidney was determined to see whether modifications of desatu ration rate, if any, were reflected in the tissue fatty acid profiles. Animals fed for 12 wk on a balanced diet, containing 20:4n-6 and 18:2 n-6, were compared to those fed 18:2n-6 only. The low amount of dietar y 20:4n-6 greatly inhibited Delta 6 desaturation of 18:2n-6 and Delta 5 desaturation of 20:3n-6, whereas Delta 6 desaturation of 18:3n-3 was slightly increased in obese rats. Inhibition of the biosynthesis of l ong-chain n-6 fatty acids by dietary arachidonic acid was only slightl y reflected in the 20:4n-6 content of liver microsome phospholipids. O n the contrary, the enrichment of serum total lipids and heart and kid ney phospholipids in this fatty acid was pronounced, more in obese tha n in lean animals. Our results show that, although the desaturation ra te of the n-6 fatty acids in liver microsomes was greatly decreased by the presence of arachidonic acid in the diet, the tissue phospholipid content in arachidonic acid was not depressed. The potentiality of sy nthesis of eicosanoids of the 2 family from this fatty acid is consequ ently not lower, especially in obese rats, in which certain tissues ar e deficient in arachidonic acid, in comparison with their lean litterm ates.