Acute changes of the conversion of thyroxine to triiodothyronine in hypophysectomized and thyroidectomized chickens exposed to mild cold (10 degrees).

The effect of acute cold (10 degrees) exposure on the tissue level of triiodothyronine (T3) and on the conversion of thyroxine (T4) to triiodothyronine, both in vitro and in vivo, has been investigated in young chickens previously thyroidectomized or hypophysectomized. It was found that cold exposure stimulates T4 to T3 conversion both in vivo and in vitro not only in intact animals but also in hypophysectomized and thyroidectomized ones. It is concluded that peripheral metabolism of thyroid hormones represents a self-standing but not sole route of adaptation to changes in environmental temperature.