The ratio of n‐6 to n‐3 polyunsaturated fatty acids in the rat diet alters serum lipid levels and lymphocyte functions

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 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.

Influence of Diets Containing Olive Oil, Sunflower Oil or Hydrogenated Coconut Oil on the Immune Response of Mice.

“…Several studies have reported that feeding experimental animals or humans a diet containing (n-3) PUFA inhibits lymphocyte proliferation [3,29]. Our results are partially consistent with such findings, since we observed an increase in lymphocyte proliferation, when we have provided diets containing olive oil or hydrogenated coconut oil compared with such inhibition in mice fed the diet containing sunflower oil, where we observed a light reduction in lymphocyte proliferation.…”

A comparison of the capacity of six cold-pressed plant oils to support development of acquired immune competence in the weanling mouse: superiority of low-linoleic-acid oils

“…A small body of previous work pertains to flaxseed oil which has appeared depressive of cell-mediated immune competence relative to n-6-rich oils in some studies (Fritsche et al 1991;Jeffery et al 1996), but either was not different from n-6-rich oils in this respect (Marshall & Johnston, 1985) or was stimulatory (Kelley et al 1988;Fritsche & Johnston, 1990) in other studies. The inconsistencies among studies do not appear related to the indices used to assess immune competence, but may relate to oil quality.…”

Effects of Different Levels of Hemp Seed (Cannabis SativaL.) and Dextran Oligosaccharide on Growth Performance and Antibody Titer Response of Broiler Chickens

“…Serum samples were separated into sterile plain tubes and stored in a refrigerator for analyses. Total antibody production specific for NDV vaccine or IBV vaccine was determined in serum by means of an ELISA using commercial ELISA test kits (IDEXX Laboratories Inc., Westbrook, ME, USA) (Jeffery et al, 1996). One microliter of serum was diluted 1:500 in 3.3 , 5.5 -tetramethylbenzidine (TMB) diluents.…”