Dietary linoleic acid and polyunsaturated fatty acids in rat brain and other organs. Minimal requirements of linoleic acid

Starting three weeks before mating, 12 groups of female rats were fed different amounts of linoleic acid (18∶2n−6). Their male pups were killed when 21‐days‐old. Varying the dietary 18∶2n−6 content between 150 and 6200 mg/100 g food intake had the following results. Linoleic acid levels remained very low in brain, myelin, synaptosomes, and retina. In contrast, 18∶2n−6 levels increased in sciatic nerve. In heart, linoleic acid levels were high, but were not related to dietary linoleic acid intake. Levels of 18∶2n−6 were significantly increased in liver, lung, kidney, and testicle and were even higher in muscle and adipose tissue. On the other hand, in heart a constant amount of 18∶2n−6 was found at a low level of dietary 18∶2n−6. Constant levels of arachidonic acid (20∶4n−6) were reached at 150 mg/100 g diet in all nerve structures, and at 300 mg/100g diet in testicle and muscle, at 800 mg/100 g diet in kidney, and at 1200 mg/100 g diet in liver, lung, and heart. Constant adrenic acid (22∶4n−6) levels were obtained at 150, 900, and 1200 mg/100 g diet in myelin, sciatic nerve, and brain, respectively. Minimal levels were difficult to determine. In all fractions examined accumulation of docosapentaenoic acid (22∶5n−6) was the most direct and specific consequence of increasing amounts of dietary 18∶2n−6. Tissue eicosapentaenoic acid (20∶5n−3) and 22∶5n−3 levels were relatively independent of dietary 18∶2n−6 intake, except in lung, liver, and kidney. In several organs (muscle, lung, kidney, liver, heart) as well as in myelin, very low levels of dietary linoleic acid led to an increase in 20∶5n−3. Dietary requirements for 18∶2n−6 varied from 150 to 1200 mg/100 g food intake, depending on the organ and the nature of the tissue fatty acid. Therefore, the minimum dietary requirement is estimated to be about 1200 mg/100 g (i.e., the level that ensures stable and constant amounts of arachidonic acid).