Effect of thyroid status on lipid composition and peroxidation in the mouse liver

In order to analyze the possible relationship between metabolic rate and ox idative stress, OF1 female mice were rendered hyper- or hypothyroid for 4-5 weeks by administration of 0.0012%L-thyroxine (T-4) or 0.05% 6-n-propyl-2- thiouracil (PTU), respectively, in their drinking water. Treatment with T-4 -resulted in increased basal metabolic rate measured by oxygen consumption and liver cytochrome oxidase activity without altering the glutathione redo x system. Endogenous lipid peroxidation, sensitivity to lipid peroxidation and fatty acid unsaturation were decreased in the hyperthyroid group. Hypot hyroidism also decreased phosphatidylcholine and cardiolipin fatty acid uns aturation but not in total lipids, and thus lipid peroxidation was not alte red. Cardiolipin, a mainly mitochondrial lipid, was the most profoundly alt ered fraction by both hyper- and hypothyroidism. It is suggested that the l ipid changes observed in hyperthyroid animals can protect them against an i ncreased oxidative attack to tissue lipids due to their increased mitochond rial activities. (C) 1998 Elsevier Science Inc.