Morphological demonstration and quantification of TSH binding sites in neoplastic and non-neoplastic thyroid tissues. An autoradiographic study using 125I-labelled thyrotropin.

We have developed a morphological method to portray TSH binding sites in intact tissue specimens. Frozen sections were incubated with 125I-labelled TSH so as to localise binding sites by autoradiography. The proof of specificity was substantiated by: the competitive inhibition of 125I-TSH-labelling with cold TSH, the lack of binding in non-target tissues and a lack of binding in TSH target tissues after incubation with 125I-hCG or free 125I. In applying this method to a total of 22 surgical specimens of thyroid, striking differences came to light in respect of the degree to which 125I-TSH binding occurred in the various thyroid disorders. When compared with histologically normal tissue, labelling was generally decreased in toxic adenomas, non-functioning adenomas (cold nodules), and thyroids affected by Graves' disease, whereas non-toxic colloid goitre cases clearly exhibited denser binding. Medullary and anaplastic carcinomas exhibited no specific labelling whilst binding varied in the differentiated carcinomas between no effective binding or a level resembling that found in normal thyroid tissue.