THYROTROPIN RECEPTOR MESSENGER-RIBONUCLEIC-ACID IS EXPRESSED IN MOST BROWN AND WHITE ADIPOSE TISSUES IN THE GUINEA-PIG

High affinity TSH binding has been reported in a variety of tissues ot her than the thyroid, most commonly in adipocytes and lymphocytes. Thi s extrathyroidal binding of TSH has been documented most carefully in the guinea pig epididymal fat pad, where it has been postulated to be due to the presence of the TSH receptor (TSH-R). Extrathyroidal TSH-R expression has also been theorized to account for the associated dermo pathy and ophthalmopathy seen in some patients with Graves' disease. W e have isolated a cDNA encoding a fragment of the guinea pig TSH-R and have used this as a probe to study the distribution of TSH-R mRNA in the guinea pig. We show here that TSH-R mRNA is expressed in most whit e adipose tissues and in all brown adipose tissues tested. However, no expression was detectable by Northern analysis or in most polymerase chain reaction experiments using guinea pig retroorbital tissues, brin ging into question the proposed role of the TSH-R as an autoantigen in autoimmune ophthalmopathy. The presence of significant amounts of TSH -R mRNA in most adipose tissues suggests a more important role for TSH in lipolysis and thermogenesis than previously thought.