LOW-LEVELS OF EICOSAPENTAENOIC AND DOCOSAHEXAENOIC ACIDS MIMIC THE EFFECTS OF FISH-OIL UPON RAT LYMPHOCYTES

Fish oil is rich in the long chain n-3 polyunsaturated fatty acids eic osapentaenoic acid (EPA) and docosahexaenoic acid (DHA); typically the se fatty acids constitute 20 to 25 g/100 g total fatty acids in fish o il. Feeding rodents diets rich in fish oil has been shown to decrease lymphocyte proliferation and natural killer cell activity. It is not k nown what level of EPA + DHA is required in the diet to exert these ef fects. This question was addressed in the current study. Weanling rats were fed on high fat (178 g/kg) diets which contained 4.4 g alpha-lin olenic acid (control) or 4.4 g EPA + DHA (4.4 EPA + DHA) or 6.6 g EPA + DHA (6.6 EPA + DHA)/100 g total fatty acids. The n-6 to n-3 polyunsa turated fatty acid ratio was maintained at approximately 7. The fatty acid compositions of the serum and of spleen leukocytes were markedly influenced by that of the diet. Spleen lymphocyte proliferation in res ponse to concanavalin A, spleen natural killer cell activity and PGE(2 ) production by spleen leukocytes were reduced by feeding the EPA + DH A diets compared with feeding the control diet; the 4.4 and 6.6 EPA DHA diets caused very similar reductions. The 4.4 EPA + DHA diet reduc ed popliteal lymph node weight following a localised graft versus host response; this response was not investigated in rats fed the 6.6 EPA + DHA diet. The reductions in lymphocyte functions and in the in vivo graft versus host response caused by the EPA + DHA diets were similar to those previously reported following the feeding of diets rich in fi sh oil. Thus, this study shows that diets containing relatively low le vels of EPA + DHA (20 to 25% of the level found in fish oil) exert imm unomodulatory effects. Furthermore, this study suggests that the maxim al effect of EPA + DHA is exerted when these fatty acids constitute a level of less than or equal to 4.4 g/100 g total dietary fatty acids.