LEVEL OF POLYUNSATURATED FATTY-ACIDS AND THE N-6 TO N-3 POLYUNSATURATED FATTY-ACID RATIO IN THE RAT DIET ALTER SERUM-LIPID LEVELS AND LYMPHOCYTE FUNCTIONS

In order to further examine the effects of dietary polyunsaturated fat ty acids (PUFA) upon blood lipid levels and lymphocyte functions, wean ling rats were fed for 6 weeks on high fat (178 g/kg) diets which diff ered in the ratio of n-6:n-3 PUFA(100, 20, 10, 5, 1) and in the absolu te level of PUFA(17.5 or 35 g/100 g fatty acids). The n-6:n-3 PUFA rat io of the diets was decreased by replacing linoleic acid with alpha-li nolenic acid while the PUFA content of the diets was decreased by repl acing PUFA with palmitic acid. Serum cholesterol concentrations decrea sed as the n-6:n-3 PUFA ratio of the low PUFA diet decreased. The ex v ivo proliferation of spleen lymphocytes from rats fed the low PUFA die ts decreased as the n-6:n-3 PUFA ratio of the diet decreased; the prol iferation of spleen lymphocytes from high PUFA-fed rats was less affec ted by the n-6:n-3 PUFA ratio of the diet. Natural killer cell activit y was lower for spleen lymphocytes from rats fed high PUFA diets with n-6:n-3 PUFA ratios of 100 or 20 than for those from rats fed low PUFA diets with these ratios. The natural killer cell activity of spleen l ymphocytes decreased as the n-6:n-3 PUFA ratio of the law PUFA diet de creased. These findings indicate that dietary alpha-linolenic acid has significant blood lipid-lowering and immunomodulatory effects in rats , but that the effect is dependent upon the total PU FA content of the diet. The ratios of linoleic and alpha-linolenic acids to other fatty acids (e.g. palmitic, oleic) are important in determining the precise effect of manipulations of the fatty acid composition of the diet.