Thyrotropin receptors in brown adipose tissue: Thyrotropin stimulates typeII iodothyronine deiodinase and uncoupling protein-1 in brown adipocytes

It has been demonstrated that TSH receptors are expressed not only in thyro id gland but also in extrathyroidal tissues. Brown adipose tissue of guinea pig has been reported to express TSH receptor messenger RNA (mRNA), but th e physiological roles of TSH receptors in brown adipose tissue have not bee n understood. We studied the expression and function of TSH receptors in ra t brown adipose tissue and cultured rat brown adipocytes. Northern analysis demonstrated the expression of TSH receptor mRNA in rat brown adipose tiss ue and cultured rat brown adipocytes. TSH receptor mRNA in rat brown adipos e tissue was decreased by cold exposure of the rat, and its mRNA in culture d rat brown adipocytes was also decreased by incubation with TSH or (Bu)(2) cAMP. TSH increased the intracellular cAMP concentration in cultured rat br own adipocytes in a dose-dependent manner. Type II iodothyronine deiodinase mRNA, its activity, and uncoupling protein-1 mRNA in cultured rat brown ad ipocytes were significantly increased by incubation with TSH in a dose-depe ndent manner. These results suggest the expression of functional TSH recept ors in brown adipose tissue, which may be involved in regulation of the exp ression of type II iodothyronine deiodinase and uncoupling protein-1.