Effect of magnesium deficiency on Δ6 desaturase activity and fatty acid composition of rat liver microsomes

Experimental Mg 2+ deficiency was induced in a group of rats by feeding them a Mg 2+ ‐deficient diet for 23 days. They were pair‐fed to compare with a control group of rats fed a Mg 2+ ‐sufficient diet. In the Mg 2+ ‐deficient group the plasma total cholesterol and triglyceride levels were increased while HDL‐cholesterol was decreased. In the Mg 2+ ‐deficient group the plasma level of thiobarbituric acid reacting substances (TBARS) used as a measure for lipid peroxidation was increased. The increase was attributed to the increased cytosolic Ca 2+ in Mg 2+ ‐deficiency which can cause: 1) increase of hydro and endoperoxide levels as a consequence of the increase of arachidonic acid release and eicosanoid synthesis in Mg 2+ ‐deficiency, and 2) inhibition of the mitochondrial respiratory activity and activation of Ca 2+ ‐dependent proteases which may activate the conversion of xanthine dehydrogenase to xanthine oxidase which generates active O 2 species. In the Mg 2+ ‐deficient group, the fatty acid composition of the liver microsomes indicated a slower rate of conversion of linoleic acid to arachidonic acid which was consistent with the decrease of Δ6 desaturase activity in liver microsomes of Mg 2+ ‐deficient rats as measured in vitro . The decrease of Δ6 desaturase activity was attributed to the lower concentration of actual enzyme molecules as a result of the decreased rate of protein synthesis in Mg 2+ ‐deficiency. The possible effects of the increased catecholamine release in Mg 2+ ‐deficiency are discussed.