Dietary cholesterol and/or n − 3 fatty acid modulate Δ9-desaturase activity in rat liver microsomes

Abstract

Δ 9-Desaturase activity and fatty acid composition of liver microsomal phospholipids in rats fed diets enriched with either saturated (hydrogenated beef tallow) or α-linolenic (linseed oil) or eicosapentaenoic and docosahexaenoic (fish oil) acids with or without 2% cholesterol supplementation were investigated. Both the linseed oil and the fish oil diets inhibited Δ 9-desaturase activity in the rat liver microsomes. The inhibition was greater when feeding fish oil (90%) compared with the linseed oil (60%) diet. Dietary cholesterol feeding accelerated conversion of palmitic (16:0) to palmitoleic (16:1) acid, irrespective of the fatty acid supplement. Feeding the linseed oil diet decreased, while feeding the fish oil diet increased synthesis of the monounsaturated fatty acids of n − 7 series (palmitoleic and vaccenic acid) and decreased 18: 1( n − 9) in microsomal membrane lipids when compared with animals fed beef tallow. Addition of 2% cholesterol to the otherwise low cholesterol diets led to accumulation of 16:1( n − 7), 18:1( n − 7) and 18:1( n − 9) in microsomal membranes. These results suggest that Δ 9-desaturase activity is dependent on the cholesterol content as well as the n − 3 fatty acid content of microsomal membranes on which it is localized.