Effects of dietary n-3/n-6 and polyunsaturated fatty acid/saturated fatty acid ratios on platelet aggregation and lipid metabolism in rats

We studied the effects of dietary lipids on platelet aggregation and lipid metabolism in rats by varying the n-3/n-6 ration while maintaining the polyunsaturated fatty acid/saturated fatty acid (P/S) ratio fixed, and vice versa. After two weeks, the platelet counts decreased as the dietary n-3/n-6 ratio rose, and platelet aggregation was sufficiently suppressed at the ratio of 0.2. Differences in the dietary P/S ratio, however, did not affect either the platelet counts nor platelet aggregation. As the dietary n-3/n-6 ratio rose, the proportion of arachidonic acid (AA) in the plasma and the phospholipids (PL) of the platelets and aorta decreased gradually, whereas the proportion of eicosapentaenoic acid (EPA) in each tissue increased gradually. The proportion of EPA was higher in the platelets than in the aorta, while that of docosahexaenoic acid (DHA) was higher in the latter. The production of platelet thromboxane A(2) (TXA(2)) and aortic prostacyclin (PGI(2)) showed sharp declines, from the values for the n-3/n-6 ratio of 0.02 (control) to those for 0.5. These results suggest that the n-3/n-6 ratio of dietary fats necessary to ensure the suppression of platelet aggregation in normal rats would be at least 0.2 and no more than 0.5.