High-Molecular-Weight Serum Thyrotropin Revisited

To the Editor: A high-molecular-weight form of thyrotropin (>200,000 daltons) with reduced potency in adenylate cyclase assays but the ability to bind normally to the thyrotropin receptor was the only radioimmunoassayable thyrotropin in a healthy young man. This subject, whom we previously described in the Journal, was euthyroid, although thyrotropin levels in his serum were more than 50 times higher than in normal persons.¹ When the “large thyrotropin” was chromatographed on Sephacryl S-200, in the presence of 3 M guanidine hydrochloride, about 40 percent of the thyrotropin immunoreactivity appeared in the fractions where standard human thyrotropin elutes. Standard human…