Effect of dietary fats on the δ6- and δ5-desaturation of fatty acids in rat liver microsomes

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Abstract
1. Rats were given diets containing (% dietary energy): 46 arachis oil (AO), 36 partially-hydrogenated arachis oil (HAO) + 10 AO, 36 partially-hydrogenated marine oil (HMO) + 10 AO, or 46 of a combination of rape-seed oils high and low in erucic acid (RSO + LERSO).2. In the liver microsomes the content of arachidonic acid (20:4ω6) was reduced inthe groups given HAO + AO and HMO + AO.3. The rates of Δ6-desaturation of linoleic acid into γ-linolenic acid (18:3ω6) and of Δ5-desaturation of dihomo-γ-linolenic acid into arachidonic acid were studied in vitro at two substrate levels: a high substrate level reflecting maximal microsomal desaturase activity in rat liver and a low substrate level reflecting desaturase activity under physiological conditions.4. Dietary HAO, rich in 18:1 isomers, suppressed the Δ6-desaturase activity butnot the Δ5-desaturase activity. Dietary HMO, rich in 18:1, 20:1 and 22:1 isomers, reduced both Δ6- and Δ5-desaturase activities.

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