Thyroid hormone deiodinases in purified primary glial cell cultures.

Iodothyronine metabolism was studied in neuroglial cells prepared from neonatal rat cerebri. Astrocytes account for nearly all of the deiodinase activity in mixed glial cell cultures. The predominant pathway is 5-deiodination, which closely resembles the enzyme activity in homogenates of cerebral cortex. Astrocytes cultured in serum-free chemically defined medium show a gradual decrease in 5-deiodination and an increase in 5'-deiodination. Exposure of cells to triiodothyronine partially reverses these changes. Thus, astrocytes contain enzymes for both major deiodinative pathways and may play a role in the regulation of thyroid hormone levels in the brain.