A simultaneous stimulation of the peroxidase activity in the thyroid gland and the hepatic monodeiodination, associated with a decrease in hepatic thiol groups, during chronic cold exposure of rats

Abstract

Male Wistar rats were subjected to a 16-day long cold exposure of 4°C. These rats are characterized by a higher food intake, but a slower growth rate. The plasma thyroxine (T 4) concentration is decreased and the triiodothyronine (T 3) concentration is increased while the reverse triiodothyronine (rT 3) level remains unchanged during the cold period. At the end of the cold exposure an increased 5′ monodeiodinating activity in the liver is observed whereas at the same time the liver total, as well as the non-protein −SH concentration, is significantly decreased. In the kidney the 5′monodeiodination and the SH concentration remain unchanged after the cold exposure. In the cold exposed rats the increased peroxidase activity in the thyroid gland is associated with significant decreased levels of T 4 and unchanged levels of T 3 in the thyroid homogenate. These results suggest that the altered thyroid hormone levels after cold exposure are caused by a simultaneous stimulation of the thyroid gland function and the 5′ monodeiodination in the liver.