THYROTROPIN RECEPTOR EXPRESSION IN ADRENAL, KIDNEY, AND THYMUS

Because the thyrotropin receptor (TSHR) has long been considered a thy roid-specific protein, its presence in extrathyroidal tissues has been controversial. In this study, we sought to detect and quantify this p otentially low abundance mRNA in various extrathyroidal tissues using liquid hybridization analysis (LHA) and to detect protein with immunoh istochemical studies. Strongly positive protected bands, indicating th e presence of both intact (2.4 kb) and variant (1.3 kb) TSHr mRNA, wer e apparent in LHA gel lanes corresponding to normal thyroid, Graves' t hyroid, and thymus. Less abundant protected bands of the same sizes we re present in lanes corresponding to normal adrenal, and samples from normal kidney were faintly positive. The full-length transcript:varian t transcript ratio was approximately 1:1 in all positive tissues. Immu nohistochemical analysis of TSHR-like reactivity in paraffin-embedded thymus, adrenal, and kidney revealed specific staining in each of thes e tissues. No TSHR mRNA or TSHR-like immunoreactivity was detected in samples from several other normal human tissues. We conclude that meas urable TSHR mRNA and protein expression is not restricted to the thyro id gland. Further study is warranted to determine whether these extrat hyroidal receptors play a role in normal physiology or in disease.