Effects of hypothyroidism on RNA synthesis in the adult rat brain.

In this study we investigated the effects of hypothyroidism on adult brain RNA synthesis. Our data show that in the cerebral hemispheres of hypothyroid rats there is a decrease in microsomal RNA content and microsomal [3H]uridine incorporation. Sucrose gradient analysis revealed that these changes are mainly associated with free ribosomes and subunits and reflect changes in rRNA. The above changes are accompanied by a decrease in RNA polymerase I activity. All of the above mentioned changes returned to normal after thyroxine (T4) treatment. In contrast to RNA polymerase I, RNA polymerase II activity was not affected. However, electrophoretic analysis of the in vitro poly(A)+RNA translation products revealed that hypothyroidism affects a few mRNAs. These results indicate that thyroid hormones have a role in adult brain tissue metabolism.