ESTIMATION OF THYROXINE OUTPUT BY THE THYROID GLANDS OF NORMAL AND ADRENALECTOMIZED RATS BY MEANS OF A SIMPLE COOLING TEST

Abstract

Adrenalectomy, administration of propylthiouracil (PTU), or a combination of these two treatments significantly increased rate of cooling of rats restrained and subjected to air at 5 °C. Propylthiouracil administration increased rate of cooling 55% above that of untreated control rats while adrenalectomy increased rate of cooling 84%. The combination of these two treatments increased rate of cooling 94%. Dead rats cooled 201% faster than control rats. Administration of graded doses of thyroxine to both adrenalectomized PTU-treated rats and to normal PTU-treated rats indicated that 1.9 and 4.4 μg/day of thyroxine respectively was required to return rate of cooling to that of comparable controls. These doses are therefore best estimates of daily thyroxine outputs by thyroid glands of these animals. The results suggest that adrenalectomy is accompanied by diminished thyroid function.