Previous studies have reported that feeding rats diets rich in fish oils, which contain high proportions of the n-3 polyunsaturated fatty acids (PUFA) eicosapentaenoic and docosahexaenoic acids, results in lowering of blood lipid levels and suppression of lymphocyte functions tested ex vivo and in vivo. The effects of other n-3 PUFA, such as alpha-linolenic acid, which is found in high proportions in linseed oil, are not as well documented. Therefore, in the present study, weanling male rats were fed for six weeks on one of five high-fat (20% by weight) diets made by mixing together sunflower and linseed oils; the resulting blends had n-6/n-3 PUFA ratios of 112.5:1 (pure sunflower oil), 14.8:1, 6.5:1, 0.81:1, and 0.33:1 (pure linseed oil); the levels of all other components in the diet were identical. The final body weight and total dissectable fat were lowest in rats fed the pure linseed oil diet. Serum cholesterol, triacylglycerol and nonesterified fatty acid concentrations decreased as the n-6/n-3 PUFA ratio of the diet decreased. The fatty acid composition of the serum and of spleen lymphocytes was influenced by the diet fed-there was a progressive decrease in the proportions of linoleic and arachidonic acids and a progressive increase in the proportion of alpha-linolenic acid as the n-6/n-3 PUFA ratio of the diet decreased. Eicosapentaenoic and docosahexaenoic acids were detected in the serum but not in spleen lymphocytes. Inclusion of alpha-linolenic acid in the diet resulted in significant suppression of spleen lymphocyte proliferation in response to the T-cell mitogen concanavalin A and in spleen lymphocyte natural killer cell activity, both measured ex vivo. The localized graft vs. host response, a measure of cell-mediated immunity in vivo, progressively decreased as the n-6/n-3 PUFA ratio of the diet decreased. Thus, this study shows that dietary alpha-linolenic acid results in lowered blood lipid levels and suppressed lymphocyte functions ex vivo and in vivo. With respect to these effects, alpha-linolenic acid is as potent as dietary fish oil.

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The average UK diet derives 16 % of its calories from saturated fatty acids [l]. It has previously been demonstrated that diets rich in certain polyunsaturated fatty acids limit the amount of adipose tissue deposited in the rat [2]. However, little is known about the effect of feeding diets rich in a particular saturated fatty acid on adipose tissue deposition in the rat. This will be examined in the present study.Male weanling Lewis rats (at least 5 animals per diet) were fed for 6 weeks on diets containing 178 g k g fat which differed in the major saturated fatty acid present. Diet A contained 39 % stearic acid (18:O); diet B contained 35 % palmitic acid (16:O); diet C contained 25 % lauric acid (12:O) and diet D contained the 24 % caprylic acid (8:O) and 17 % capric acid (1O:O). After sacrifice, the final body weight (FBW) of the animals was recorded before removing two intra-abdominal adipose depots, the epididymal fat pad (EpFP) and the dorsal wall of abdomen (DWA) depot. TheEpFP and DWA depots were chosen as it has previously been found that these depots are the most responsive to dietary manipulation [2].

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Biochemical Society Transactions ( 1 996) 24 175sThe effect of dietary lipid manipulation on the uptake of [3H]-triolein by tissues of the rat.