Interaction between fish and vegetable oils in relation to rat leucocyte leukotriene production.

We examined the influence of mixtures of dietary fish oil and three vegetable oils (linseed, olive and sunflower) on the incorporation of dietary eicosapentaenoic acid (EPA) into rat leucocyte phospholipids and the subsequent metabolism of EPA and arachidonic acid by 5-lipoxygenase. Eicosapentaenoic acid in leucocyte phospholipids of fish oil-fed rats was decreased by the addition of each vegetable oil to the dietary fish oil, with sunflower oil, the oil highest in linoleate (LA), having the largest EPA-lowering effect (66% decrease). The rate of synthesis of leukotriene B4 (LTB4) was increased by the addition of each vegetable oil to the basic fish oil diet, with sunflower oil having a significant effect on LTB4 synthesis (145% increase). The effects of olive oil (enriched in oleate) were similar to those of linseed oil (enriched in alpha-linolenic acid) with regard to EPA incorporation (mean decrease = 30%) and LTB4 synthesis (mean increase = 72%). The level of arachidonic acid in leucocyte membranes and the rate of synthesis of LTB4 were proportional to the level of dietary LA added to the basic fish oil diet. The results indicate that olive or linseed oil ingested in combination with fish oil have less effect than does sunflower oil on leucocyte EPA content and LTB4 production. They further suggest that, when ingested with fish oil, dietary linoleic acid is more important than oleate or alpha-linolenic acid as a determinant of these variables.