Lack of dose response by dietary n−3 fatty acids at a constant ratio of n−3 to n−6 fatty acids in suppressing eicosanoid biosynthesis from arachidonic acid

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Abstract
This study evaluated whether it is the ratio of n−3 to n−6 fatty acids or the absolute amount of n−3 fatty acids in diets that determines the degree of inhibition of eicosanoid biosynthesis from arachidonic acid (AA). Rats were fed diets containing different doses of linolenic acid or menhaden oil for 3 mo. Constant ratios of n−3 to n−6 fatty acids were maintained by concomitant increases in safflower oil as the n−6 fatty acid source. Results showed that AA concentrations in liver, platelet, and lung phospholipids and concentrations of eicosa-noids synthesized in tissues were significantly (P < 0.05) suppressed both by linolenic acid and menhaden oil; however, there was a lack of a dose response within groups fed different amounts of the same dietary fat. These results indicate that the ratio of n−3 to n−6 fatty acids in the diets, rather than the absolute amount of n−3 fatty acids, is the determining factor in inhibiting eicosanoid biosynthesis from AA.