The mixed unsaturated glycerides of liqud fats. IV. Low-temperature crystallisation of whale oil

Biosynthesis of prostanoids, tissue fatty acid composition and thrombotic parameters in rats fed diets enriched with docosahexaenoic (22:6n3) or eicosapentaenoic (20:5n3) acids

The objective of this experiment was to elucidate the effect(s) of eicosapentaenoic (20:5n3) vs docosahexaenoic (22:6n3) acid on prostaglandin biosynthesis and related thrombotic parameters. Diets were formulated to contain oils absent in (control) or enriched with either 20:5n3) EPA) or 22:6n3 (DHA). The diets were fed to rats for three weeks and the following evaluated: 1) bleeding time; 2) blood viscosity; 3) platelet aggregation; 4) tissue fatty acids; 5) serum thromboxane (TXB2), aortic prostacyclin (6-keto) ad 6) arachidonic acid conversion to eicosanoids by lung microsomes. There were no significant differences between treatments for bleeding time, red blood cell viscosity or platelet aggregation. In EPA fed rats 20:5n3 increased significantly in platelet and aorta phospholipids. In platelets and aorta 20:4n6 was slightly decreased in EPA and DHA animals. Platelet 22:6n3 levels were not altered by treatment, but 22:6n3 increased in the aorta of EPA and DHA fed rats. Similar changes were noted in lung and liver fatty acid composition. Serum TXB2 levels were significantly decreased only in the EPA vs control group. No differences were noted for aortic 6-keto levels or in the amount of hydroxy fatty acids, PGE, TXB2 or PGF2 alpha produced by lung microsomes. While fish oils have been shown to alter hematologic parameters in humans this study suggests that the rat is not similarly affected. Furthermore, it is evident that in the rat, 20:5n3 and not 22:6n3 is responsible for the alterations in platelet prostaglandin biosynthesis; however, these observations may not be directly applicable to other species.

Resistance of certain long-chain polyunsaturated fatty acids of marine oils to pancreatic lipase hydrolysis

When whale oil triglycerides were subjected to pancreatic lipase hydrolysis, eicosapentaenoic and docosahexaenoic acids were found mainly in the di- and triglyceride products, suggesting that they are in the 1,3-positions but resistant to the action of the lipase. Their presence in the 1,3-positions was confirmed. Their resistance to pancreatic lipase hydrolysis was demonstrated by analysis of the products of the enzyme action on: (a) a concentrate of highly unsaturated whale oil triglycerides; (b) the latter after randomization; and (c) synthetic 1,2-di-octadecenoyl-3-eicosapentaenoyl glycerol.Docosapentaenoic acid was also shown to be present in the 1,3-position of whale oil triglycerides but was not lipase resistant. It is postulated that the presence of a double bond near the carboxyl group exercises an inhibitory effect, or that the location of the double bonds in the resistant acids places their terminal methyl groups close to the carboxyl, producing a steric hindrance effect.