ELIMINATION AND METABOLISM OF TRIIODOTHYRONINE DEPEND ON THE THYROID STATUS IN THE BRAIN OF YOUNG CHICKENS

The hypothyroid chicken brain has been found to preserve more triiodot hyronine (T-3) than expected from plasma T-3 levels. A possible explan ation is that the elimination of Tg from the hypothyroid brain is decr eased. In the present experiments, the elimination rate of T-3 was com pared in surgically thyroidectomized animals and sham-operated control s. It was found that both T-3 coming from the plasma and T-3 derived l ocally in the cells from thyroxine have a significantly lower eliminat ion rate in thyroidectomized chickens than in sham-operated ones. Ther efore it is concluded that the adaptation of the brain to hypothyroid conditions is partly regulated by reducing the loss of the active thyr oid hormone (i.e. T-3) via metabolic and tissue-to-plasma exchange.