Regulation of Rat Liver Glycerophospholipid Fatty Acid Composition in Hypo- and Hyperthyroidism

The fatty acid composition of microsomal phospholipids isolated from rat liver has been shown to be altered in hyperthyroidism and hypothyroidism (1–4). In hypothyroidism, the proportions of linoleic (C18:2ω6), eicosatrienoic (C20:3ω6), eicosapentaenoic (C20:5ω3), and docosahexaenoic (C22: 6ω3) acids were increased, while the proportion of arachidonic (C20:4ω6) acid was decreased (2). In contrast, chronic hyperthyroidism increased the proportions of stearic (C18:0) acid and C20:4ω6 and concomitantly decreased the proportions of palmitic (C16:0) acid, palmitoleic (C16:1ω9) acid, C18: 2ω6 and C20:3ω6 (1). The increased C18:2ω6 and decreased C20:4ω6 in hypothyroidism may be due to diminished fatty acid desaturation (Δ6 desaturase). However, in hyperthyroidism, changes in C18:2ω6 and C20:4ω6 are reversed without evidence of increased Δ6 desaturase activity. Furthermore, the other changes in fatty acid composition cannot be readily explained by the observed alterations in fatty acid desaturation and in many cases are opposite to that predicted by the altered desaturation (1,2).