CHANGES IN PHOSPHOGLYCERIDE FATTY ACIDS OF RAT BRAIN INDUCED BY LINOLEIC AND LINOLENIC ACIDS AFTER PRE‐ AND POST‐NATAL FAT DEPRIVATION

— Pregnant rats were maintained on a fat‐free diet, starting at 10–12 days after impregnation and the offspring continued on the diet during a developmental period of 120 days. Brain fatty acids showed decreases in the level of (n‐3) and (n‐6) fatty acids of brain phophoglycerides, except for 22:5 (n‐6) which increased. These changes preceded an increase in the (n‐9) fatty acids (20:3 and 22:3). Supplementation with either linoleic or linolenic acid for 10 or 30 days after induction of the deficiency state caused an increase in the (n‐6) and (n‐3) fatty acids respectively, to control levels. The level of 22:5 (n‐6) was increased additionally by linoleic supplementation while linolenic refeeding to deficient animals decreased 22:5 (n‐6) to near control levels. The anomalous results obtained on 22:5 (n‐6) with 18:3 (n‐3) supplementation is attributed to competitive inhibition of linoleate desaturation by linolenate. Linoleic and linolenic acid were equally effective in reducing the elevated levels of the (n‐9) fatty acids toward control levels, although control levels with either fatty acid was not reached after 30 days supplementation. The increase of the (n‐6) and (n‐3) fatty acids to normal values precedes the decrease of (n‐9) fatty acids following supplementation of linoleic or linolenic acid to fat‐deficient rats. No change in fatty acid composition in control animals between 30 and 120 days was observed. In fat deficient as well as supplemented animals the total saturated, monounsaturated and polyunsatur‐ated fatty acid composition was constant as was the unsaturation index.