Rat platelet prostaglandin, cyclic AMP and lipid response to variations in dietary fat

Diets supplying 20 or 40% of the calories as fat with linoleate to saturated fatty acid ratios of 0.4, 0.8 and 5.5 were fed to male weanling rats for 8 and 11 weeks. Recalcification clotting time was not affected by dietary treatment. Concentration of cAMP in the platelets was significantly elevated at the highest level of dietary linoleate. Cyclic AMP was negatively correlated with concentration of dihomo-gamma-linolenic acid in platelet phospholipids and positively correlated with prostaglandin E1, suggesting that dihomo-gamma-linolenic acid is rapidly converted to prostaglandin E1 causing a rise of cAMP due to stimulation of adenylate cyclase. Dietary treatment did not markedly change the composition of the platelet phospholipid fatty acids and, therefore, resulted in no change in synthesis of the proaggregatory prostaglandin by platelets during clotting. Although the fatty acid composition of the platelet phospholipids remained constant, dietary treatment did affect the total amount of phospholipid fatty acid present in the platelet. Serum concentrations of cholesterol were significantly higher in rats fed the 20% fat diet than in rats fed the 40% fat diet. Platelet cholesterol followed the same trend as serum cholesterol indicating that the cholesterol content of platelets appears to reflect the lipid environment of the plasma.