| Abstract: | Exposure of a normal lean mouse to cold (14 degrees C) for 12 h increases the activity of thyroxine 5'-deiodinase in brown adipose tissue 26-fold. In contrast, exposure of the genetically obese, ob/ob, mouse to cold results in little more than a doubling of thyroxine 5'-deiodinase activity. The physiological significance of endogenous 3,5,3'-triiodothyronine production in brown adipose tissue is not understood. However, it seems likely that defective cold-induced stimulation of the 5'-deiodinase in brown adipose tissue of the ob/ob mouse might cause a relatively hypothyroid state of the tissue. Thyroid hormone is known to be required for a normal thermogenic response of brown adipose tissue to noradrenaline. It is suggested that the defect in the response of the 5'-deiodinase in the ob/ob mouse could contribute to the defective thermogenic response of brown adipose tissue to cold-exposure and to noradrenaline. |
