The nature and amount of essential fatty acids in dietary fat play a leading part in the repartition of brain polyunsaturated fatty acids (n-3 and n-6). In order to determine precisely the respective roles of linolenic and linoleic acids in the diet on rat brain development, we used two diets in which the percentage of linolenic acid (18:3 n-3) was different. The animals were fed peanut oil (group A) or rapeesed oil (group B) during pregnancy and throughout lactation. The study of the fatty acid composition of gastric milk showed that the levels of linoleic acid (18:2 n-6) and more so linolenic acid (18:3 n-3) were much lower than in dietary fats. In group B, the 18:3 n-3 level of gastric content was about four times lower (2.4%) than in the maternal diet (8.5%) at the beginning of the suckling period and significantly increased until weaning. Analysis of the fatty acid composition of ethanolamine phosphoglycerides showed that docosapentaenoic acid Δ7–10–13–16–19 (22:5 n-3) and docosahexaenoic acid Δ4–7-10–13–16–19 (22:6 n-3) levels increased in group B in relation to group A and, on the other hand, the docosapentaenoic acid Δ4–7-10–13–16 (22:5 n-6) level decreased in group B. The sum of (n-3 + n-6) fatty acids did not change in either group B or group A. In our experimental conditions, we found no marked effect of diet composition upon conversion of linoleic acid to arachidonic acid. In summary, linolenic acid can be utilized in the brain (rather than linoleic acid) to provide long-chain polyunsaturated fatty acids and the amount of n-3 fatty acids would correlate with the desaturation activity of docosatetraenoic acid Δ7–10–13–16 (22:4 n-6) to docosapentaenoic acid Δ4–7-10–13–16 (22:5 n-6).

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The influence of long duration rapeseed oil feeding with high or low levels of erucic acid has been investigated on rat heart phospholipids. The rats treated for 20 wk with rapeseed oil containing 46.2% erucic acid showed a twofold increase in the sphingomyelin content of the heart. Treatment with primor rapeseed oil (3.7% erucic acid) for 20 wk did not modify phospholipid composition of rat heart. The fatty acid patterns of phosphatidylethanolamine and phosphatidylcholine were slightly influenced by the high erucic rapeseed oil; eicosenoic acid was incorporated preferentially into position one, but erucic acid showed a random distribution in both. After high erucic rapeseed oil feeding, 22:1 was incorporated into cardiolipin (5.6%) and sphingomyelin (10.5%). The incorporation of 22:1 into sphingomyelin was associated with an increase of the percentage of 24:1 (14.6%) and a decrease of saturated long chain fatty acid (22:0, 24:0) percentages. Primor rapeseed oil caused a slight increase of 24:1 and a decrease of 22:0 and 24:0 in rat heart sphingomyelin. As cardiolipin is localized in the inner membrane of mitochondria and sphingomyelin in plasma and microsomal membranes, the acyl-moiety alterations of both phospholipids might be correlated to the pathological lesions of rat heart after a long duration of rapeseed oil feeding.

In order to determine precisely the respective roles of linolenic acid and linoleic acid in the maternal diet on rat brain subcellular fractions during development, we used two diets with different percentages of linolenic acid (18:3 n-3). The animals were fed peanut oil (group A) or soybean oil (group B) during pregnancy and throughout lactation. Nature and amount of essential fatty acids had no incidence on saturated and monounsaturated fatty acid distributions in myelin, synaptosomal, mitochondrial and microsomal fractions. In adult rats, all subcellular fractions are marked by an increase of n-3 fatty acid and a decrease of n-6 fatty acid levels in group B compared to group A. In 15-day-old animals, on the contrary, only the synaptosomal fractions are significantly affected by the diet. Independent of diet, brain development is marked by a decrease of n-6 fatty acids in all subcellular fractions; on the other hand, the n-3 fatty acid level is increased in the synaptosomal and mitochondrial fractions, and decrease in the myelin and microsomal fractions. The sum of (n-3 + n-6) fatty acids remains constant in group B and in group A in all subcellular fractions. Finally, under our experimental conditions, we found no marked effect of diet composition upon linoleic acid conversion to arachidonic acid; only the Δ4–7-10–13–16-docosapentaenoic acid (22:5 n-6) level decreased in group B. Δ7–10–13–16–19-Docosapentaenoic acid (22:5 n-3) seemed to be a better substrate for Δ4 desaturase than Δ7–10–13–16-docosatetraenoic acid (22:4 n-6).