Comparative beneficial effects on platelet functions and atherosclerosis of dietary linoleic and gamma-linolenic acids in the rabbit.

Male rabbits (10 weeks old) were fed, for 20 weeks, purified diets rich in fat (45% of calories) containing saturated fats (butter), polyunsaturated fats (evening primrose oil + butter or sunflower oil + butter) for 20 weeks. Linoleic acid represented respectively 3.6, 33 and 34% of the dietary fatty acids, while gamma-linolenic acid was present (4.4%) solely in the second group. A significant increase in di-homo-gamma-linolenic acid in plasma, platelets and aorta was noted only in the animals fed evening primrose oil. Despite this, the results of the platelet aggregation to thrombin and ADP, the recalcification plasma-clotting time (platelet-rich plasma) and the severity of atherosclerosis were not significantly different from those observed in the group fed sunflower oil. In contrast, in comparison to the butter-fed animals, the two groups fed the polyunsaturated fats showed remarkable improvements in the clotting time (P less than 0.01) and in the severity of atherosclerotic lesions (evening primrose oil P less than 0.001; sunflower oil P less than 0.05). However, the response to thrombin-induced aggregation was significantly decreased (P less than 0.05) only in the evening primrose oil-fed animals. In these long-term studies in young rabbits, dietary gamma-linolenic acid did not seem to have marked beneficial effects, additional to those induced by linoleic acid, on platelet functions or on atherosclerosis.