Effect of different thyroid state on ornithine decarboxylase activity and receptors of T3 in rat liver.

Abstract

The effects of thyreoidectomy, of the administration of 3,5,3'-triiodothyronine (T3), of thyroxine (T4) together with the inhibitor of iodothyronine 5'-deiodinase activity 6-propyl-2-thiouracil (PTU) and of PTU alone on rat liver ornithine decarboxylase (ODC) activity was studied. 28 days after thyroidectomy there was a decrease in ODC activity, whereas T3 treatment of normal rats increased enzyme activity. PTU decreased ODC activity in intact rats and inhibited ODC activity in animals treated with T4. Neither thyroidectomy T3, T4 given in vivo nor the polyamines spermine and spermidine added in vitro influenced the binding of 125I-T3 to its receptor in liver nuclei. Only addition of PTU increased Ka significantly (P less than 0.01). It is concluded that ODC activity in the liver is directly correlated with the thyroid state but not to parameters of thyroid hormone receptor in liver nuclei.