Thyroid hormone treatment alters phospholipid composition and membrane fluidity of rat brain mitochondria

We examined effects of graded doses of thyroid hormones 3,3', 5-tri-iodo-L-thyronine (T3) and L-thyroxine (T4) on the lipid composition of rat brain mitochondria. Neither hormone significantly affected the mitochondrial cholesterol or total phospholipid content, but did increase phosphatidylethanolamine (PE) at the expense of phosphatidylserine (PS), phosphatidylinositol (PI) and phosphatidylcholine (PC). The phosphatidic acid (PA) content was also elevated, suggesting enhanced phospholipid turnover. Changes in sphingomyelin (SPM) and diphosphatidylglycerol (DPG) were minimal. Mitochondrial membrane fluidity also increased after thyroid-hormone treatment, and the increase was closely correlated with PC/PE and SPM/PE molar ratios.