EFFECT OF 18-3 N-3 GEOMETRICAL-ISOMERS OF HEATED LINSEED OIL ON THE BIOSYNTHESIS OF ARACHIDONIC-ACID IN RAT

The influence of dietary heated linseed oil on the fatty acid composition of rat liver, platelet and plasma phospholipids (PL) with particular reference to the metabolism of linoleic acid (18:2 n-6) were studied. Δ6 and Δ5 desaturase activities and fatty acid composition of hepatic microsomal total lipids (TL) also were determined. Two groups of male weanling rats were fed, for 6 weeks, diets containing 10% (in weight) of a fresh linseed oil (LO group) and of a heated linseed oil (HLO group). The contents of geometrical isomers of linolenic acid (18:3 n-3) were high in the oil heated at 240°C for 10 hours. The pattern of arachidonic acid (20:4 n-6) in the different lipid fractions studied was slightly affected for the animals receiving the heated oil and the 20:4 n-6/18:2 n-6 ratios were increased. However, an accumulation of a trans fatty acid (a geometrical isomer of 20:5 n-3) and a decrease of n-3 polyunsaturated fatty acids were observed in the PL. Hepatic Δ6 desaturase activity of liver microsomes was not significantly modified after HLO feeding, compared to LO feeding. In contrast, Δ5 desaturase activity was increased. The desaturase activities were in agreement with the fatty acid profile of the microsomal TL. © 1990 Pergamon Press plc.