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-iod o-L-thyronine (T-3) and L-thyroxine (T-4) on the lipid composition of rat brain mitochondria. Neither hormone significantly affected the mit ochondrial cholesterol or total phospholipid content, but did increase phosphatidylethanolamine (PE) at the expense of phosphatidylserine (P S), phosphatidylinositol (PI) and phosphatidylcholine (PC). The phosph atidic acid (PA) content was also elevated, suggesting enhanced phosph olipid turnover. Changes in sphingomyelin (SPM) and diphosphatidylglyc erol (DPG) were minimal. Mitochondrial membrane fluidity also increase d after thyroid-hormone treatment, and the increase was closely correl ated with PC/PE and SPM/PE molar ratios.