ALTERATIONS IN CARNITINE-ACYLCARNITINE TRANSLOCASE ACTIVITY AND IN PHOSPHOLIPID-COMPOSITION IN HEART-MITOCHONDRIA FROM HYPOTHYROID RATS

Changes in mitochondrial fatty acid metabolism may underlie the declin e in cardiac function in the hypothyroid animals. The effect of hypoth yroidism on fatty acid oxidation, carnitine-acylcarnitine translocase activity and lipid composition in rat heart mitochondria has been exam ined. Rates of mitochondrial fatty acid oxidation as well as carnitine -carnitine and carnitine-palmitoylcarnitine exchange reactions were al l depressed in heart mitochondria isolated from hypothyroid rats. Kine tic analysis of the carnitine-carnitine exchange reaction showed that the hypothyroid state affects the V-max of this process, while having no effect on the K-m value. Heart mitochondrial inner membrane lipid c omposition was significantly altered in hypothyroid rats. Cardiolipin, particularly, was found to decrease (by around 36%). Alterations in f atty acid pattern of mitochondrial inner membrane preparations from hy pothyroid rats were also found. The effects of the hypothyroid state o n fatty acids oxidation, carnitine translocase activity and phospholip id composition were completely reversed by following treatment of hypo thyroid rats with thyroid hormone. A lower cardiolipin content in the mitochondrial inner membrane offers a plausible mechanism to explain t he decline in the translocase activity in hypothyroidism. (C) 1997 Els evier Science B.V.