Dose dependent effects of dietary gamma-linolenic acid on rat spleen lymphocyte functions

Feeding rodents a diet rich in evening primrose oil (EPO), which contains 5 -10 g gamma-linolenic acid (GLA)/100 g total fatty acids, has been shown to decrease lymphocyte proliferation and natural killer cell activity. Howeve r, EPO contains a very high level of linoleic acid which itself can affect lymphocyte functions and it is not clear to what extent the effects of EPO can be attributed to GLA. The current study investigated the effect of two levels of GLA in the rat diet upon immune cell functions; the level of lino leic acid was maintained below 30 g/100 g total fatty acids. Weanling rats were fed on high fat (178 g/kg) diets which contained 4.4 g or 10 g GLA/100 g total fatty acids in place of a proportion of linoleic acid. The total p olyunsaturated fatty acid content and the n-6 to n-3 polyunsaturated fatty acid ratio of the diet were maintained at 35 g/100 g total fatty acids and 7, respectively. The fatty acid compositions of the serum and of spleen leu kocytes were markedly influenced by that of the diet, with an increase in t he proportions of GLA and dihomo-gamma-linolenic acid when the diets contai ning GLA were fed; these diets also increased the proportion of arachidonic acid in spleen leukocytes. Spleen lymphocyte proliferation in response to concanavalin A was significantly reduced (by 60%) by feeding the diet conta ining the higher level of GLA, but not by the diet containing the lower lev el of GLA. Spleen natural killer cell activity and prostaglandin E (PGE) pr oduction by spleen leukocytes were not significantly affected by inclusion of GLA in the diet, although there was a tendency towards decreased natural killer cell activity by cells from rats fed the high GLA diet. Thus, this study shows that dietary GLA is capable of altering the fatty acid composit ion of cells of the immune system and of exerting some immunomodulatory eff ects, but that the level of GLA in the diet must exceed 4.4 g/100 g total f atty acids for these effects to become apparent.