n-3 fatty acids reduce in vitro thromboxane production while having little effect on in vitro prostacyclin production in the rat

Male Sprague-Dawley rats were fed diets with 50% of the energy from fat over a 20-day period. The fats used were hydrogenated beef-fat (HBF), or HBF supplemented with ethyl arachidonate A, safflower oil (SO), or a mixture of SO and linseed oil (LO). For comparative purposes, another group of animals was fed a diet providing 50% of the energy as butter-fat. In vitro aortic prostacyclin (PGI₂) and serum thromboxane (TXA₂) levels (from clotting blood) were determined by radioimmunoassay of 6-keto PGF_1α and TXB₂, respectively. The HBF diet had similar AA levels relative to the butter-fed rats but significantly reduced tissue levels of eicosapentaenoic acid (EPA) and this was associated with an increased production of serum TXB₂. Supplementing the HBF diet with AA increased tissue levels of AA while maintaining low levels of n-3 fatty acids. These changes were accompanied by significant increases of both TXB₂ and 6-keto-PGF_1α. LO supplementation to the HBF diet (with constant SO) led to elevated levels of EPA and relatively constant AA levels and this was associated with reduced producton of TXB₂. These results highlight the responsiveness of TXA₂ to n-3 fatty acids in contrast to PGI₂ which was more influenced by the level of AA in the tissue phospholipids in the rat.