Effects of thyroxine and triiodothyroacetic acid on cerebral myelin lipids

Neonatal rats, thyroidectomized at one day of age, received either no replacement therapy or daily subcutaneous injections of 100 μg/kg body weight of thyroxine (T₄) or equal molar amounts of triiodothyroacetic acid (T₃AC) from day 6 to day 26. Myelin lipid was isolated from the rat cerebrums and the cholesterol, cerebroside and total phospholipid content were determined. Cerebral myelin lipid weights were decreased in the neonatally thyroidectomized and T₄ treated rats. The myelin lipid weights of the T₃AC treated rats were not different from those treated with T₄. The lipid composition remained unchanged in the T₃AC, T₄, and thyroidectomized groups when compared with the normal rats. These results indicate that T₃AC and T₄ administration have similar effects on CNS myelination in brains of neonatally thyroidectomized rats.