Mitochondrial inner membrane in hypothyroidism

Abstract

Inner membrane vesicles obtained from the liver mitochondria of hypothyroid and normal rats were compared. In the vesicles from hypothyroid rats the rate of ATP synthesis at 30 [deg]C is 35-50% less than the normal rate. The Arrhenius profile for phosphorylation by such vesicles lacks the discontinuity at 21 [deg]C that is seen with vesicles from normal rats; at temperatures below about 9 [deg]C the rate of phosphorylation by vesicles from hypothyroid rats is not lower than normal. The phospholipids of hypothyroid vesicles contain higher mole fractions of 18:2 (linoleic), 18:3 (linolenic or [gamma]-linolenic), and 20:3 (eicosatrienoic) and lower fractions of 20:4 (arachidonic), 22:3 (docosatrienoic), and 22:4 (docosatetraenoic); the unsaturation index, mainly due to 20:4, is 10% less than in normal vesicles. Injecting hypothyroid rats with -thyroxine 3 days before preparation of vesicles corrects the relative contents of these unsaturated fatty acids as well as the Arrhenius profile and also increases the phosphorylation rate at 30 [deg]C. Respiration and cytochrome a content do not differ for membrane vesicles prepared from livers of rats in the various thyroid states. A metabolic defect in unsaturated fatty acid metabolism in hypothyroidism may be involved in the function of the inner mitochondrial membrane.