Effects of high erucic acid diet on sphingomyelin biosynthesis in rat lung microsomes

The amount of fatty acids in free ceramides and sphingomyelins and the biosynthesis of sphingomyelins were measured in lung microsomes of rats fed either a stock diet or semisynthetic diets containing 15% by weight of sunflower oil or rapeseed oil (48% erucic acid). The rapeseed oil diet increased the amount of 24 : 1 in free ceramides and decreased that of 24 : 0 in both fractions as compared to the other reference diets. Incubations of lyophilized microsomes with [14C acyl] ceramides (16 : 0, 18 : 1 or 24 : 1) and [3H methyl] phosphatidylcholine showed that in the stock and the sunflower oil diet groups the conversion kinetics of the 18 : 1 and 24 : 1 ceramides into sphingomyelins were the same while that of the 16 : 0 ceramide showed a higher affinity for the enzymatic systems. The rapeseed oil diet enhanced the apparent kinetic constants of 24 : 1 ceramide conversion. Studies on the appearance of 3H radioactivity in sphingomyelin showed that phosphorylcholine transfer from phosphatidylcholine to a ceramide acceptor occurred during sphingomyelin biosynthesis in lung microsomes. This pathway was also influenced by the rapeseed oil diet.