Metabolic Effects of Thyroxine, 3,3',5-Triiodothyronine, 3,3'-Diiodo-5-Bromothyronine and 3,3'-Diiodothyronine Administered Orally to Rats

¹ From the Department of Pharmacology, School of Medicine, University of Virginia, Charlottesville, Virginia

By using large amounts of (–) thyroxine, (–) 3,3',5-triiodothyronine, (±) 3,3'-diiodo-5-bromothyronine and (±) 3,3'-diiodothyronine in the drinking water of rats, it was found that thyroxine, triiodothyronine and 3,3'-diiodo-5-bromothyronine elevated the metabolism while 3,3'-diiodothyronine had no effect with this method of administration. It was observed that there was a limiting value to the elevation of the metabolism which was soon reached with thyroxine but not with triiodothyronine. The maximal elevation of metabolism obtained with triiodothyronine was +244 in the thyroidectomized animal and +201 in the normal animal. With thyroxine the maximal metabolism was +141 in the thyroidectomized animal and +26 in the normal animal. One hypothyroid rat showed skin changes which healed after 11 days with triiodothyronine in the drinking water.