Effect of thyroid dysfunction upon phospholipid composition and CDP-choline incorporation in mitochondria and microsomal fraction isolated from liver and brain of suckling rats.

The phospholipid composition and the in vitro incorporation of radioactive CDP-choline into phosphatidylcholine was studied in mitochondria and microsomal fraction obtained from liver and brain of 20 day old hyperthyroid or hypothyroid rats. The chemical composition of the subcellular membranes isolated from brain differed markedly in both conditions. In hyperthyroidism the microsomal fraction was slightly affected while the mitochondria were also affected, but not as severely as in hypothyroidism, in which the microsomal fraction showed no alterations. The incorporation of the radioactive precursor into brain mitochondria isolated from hyperthyroid rats was markedly decreased, while no changes were observed in microsomes. However, incorporation into brain microsomal fraction obtained from hypothyroid rats was increased, while no changes were observed in mitochondria. similar results were obtained in the studies performed with liver subcellular membranes from hyperthyroid animals while no changes were found in those from hypothyroid rats. Our results indicate that both experimental conditions affect in a different way the structure and function of brain mitochondria and microsomal fractions. They also give further support to our hypothesis that mitochondria have a certain degree of autonomy for the synthesis of phosphatidylcholine.