The influence of diet on platelet aggregation and blood pressure

Vas Dias, Floris Willem (1982) The influence of diet on platelet aggregation and blood pressure. University of Southampton, Doctoral Thesis.

Abstract

Several epidemiological studies have shown that a relationship exists between coronary heart disease (CIID) and dietary fat. These investigations demonstrated that the ingestion of dietary saturated fats is associated with a high CUD incidence and mortality, whereas dietary polyunsaturated fats appeared to reduce these. However, the studies of the Greenland Eskimos have clearly demonstrated that the use of the term polyunsaturated fat in community nutrition programmes should be qualified as to whether n-6 or n-3 polyunsaturated fatty acids are under discussion. Platelet aggregation is a central feature of atherosclerosis and thrombosis, the two main pathological events in CUD. Platelet aggregation induced by ADP, collagen, thrombin and arachidonic acid was measured in Wistar rats and New Zealand White rabbits fed on diets enriched with corn oil, linseed oil, fish oil and coconut oil, rich in C18:2, n-6, C18:3, n-3, C20:5, n-3 and medium-chain saturated fatty acids respectively. In general, the initial rate (VAmax) and maximum extent (Amax) of aggregation of platelets from Wistar rats fed corn oil enriched diets were higher than from those fed on diets supplemented with coconut oil. However, the Kaolin Cephalin clotting time of plasma from coconut oil-fed animals was significantly reduced. The inclusion in the diets of an antigenic soy protein did not appear to affect platelet aggregation. In studies with rabbits, fish oil-supplementation of diets resulted in an inhibition of platelet aggregation induced by ADP, collagen and thrombin, which was closely paralleled by changes in the fatty acid composition of platelet total lipids, particularly by increases in C20:9, n-3 and C22:6, n-3. Supplementing diets with linseed oil led to an inhibition of collagen- and thrombin induced aggregation only. No differences were observed when animals were fed corn oil- or coconut oil supplemented diets. Varying the ratio of n-3 to n-6 fatty acids resulted in increasing inhibition of aggregation with increasing amounts of dietary C18:3, n-3, when aggregation was induced by ADP, collagen and arachidonic acid. Platelet total phospholipid C20:5, n-3 was also increased. Increasirg levels of C18:3, n-3 could have suppressed the elongation and desaturation of C18:2, n-6 to C20:4, n-6, the precursor of pro-aggregatory thromboxane A2. C20:5, n-3 inhibits the incorporation of C20:4, n-6 into phospholipids and the conversion of C20:4, n-6 to TxA2 by cyclo-oxygenase. This would lead to the inhibition of platelet aggregation. The effect of obesity on aggregation was examined in lean andobese Zucker rats. The Amax and VAmax of aggregation of platelets from obese rats were higher than of those from lean animals. Dietary oils did not affect these parameters. Supplementing diets of leanrats with either linseed oil or fish oil inhibited platelet aggregation.The blood pressures of a vegetarian population are generally lower than that of omnivores. This difference could be a result of the differences in the consumption of dietary fats, fibre or protein source. The effects of dietary saturated fats and protein source on the blood pressure of rabbits were examined. Dietary saturated fat (palm- or coconut oil; 200 g/kg diet) was shown to induce hypertension. Dietary protein source did not appear to affect the blood pressure. When the dietary fat source was changed from corn oil to palm oil, the blood pressures increased significantly in rabbits fed either a vegetable protein (soya meal) or an animal protein (fish meal). Changing from palm oil to corn oil resulted in a significant increase in the fish oil fed animals only. Results also showed that salt induces hypertension in some rabbits, while others appear to be resistant. When diets were supplemented with 50 g saturated fat/kg, the increase in the blood pressures of salt-fed rabbits was significantly higher than those in rabbits fed the salt-free diet. No differences in blood pressure increases were observed when the high salt- and salt free-diets were enriched with 200 g saturated fat/kg.

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