The ratio of n-6 to n-3 polyunsaturated fatty acids in the rat diet alters serum lipid levels and lymphocyte functions |
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Authors: | N M Jeffery P Sanderson E J Sherrington E A Newsholme P C Calder |
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Affiliation: | (1) Department of Biochemistry, University of Oxford, 0X1 3QU Oxford, UK;(2) Department of Human Nutrition, University of Southampton, Bassett Crescent East, S016 7PX Southampton, UK |
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Abstract: | 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 testedex vivo andin vivo. The effects of other n-3 PUFA, such as α-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, 0.8:1, 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 α-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 α-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 measuredex vivo. The localized graft vs. host response, a measure of cellmediated immunityin vivo, progressively decreased as the n-6/n-3 PUFA ratio of the diet decreased. Thus, this study shows that dietary α-linolenic
acid results in lowered blood lipid levels and suppressed lymphocyte functionsex vivo andin vivo. With respect to these effects, α-linolenic acid is as potent as dietary fish oil. |
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