Pharmacology of bovine and human thyrotropin: an historical perspective

Before the induction of a brief period of hypothyroidism became the standard method for inducing 131I uptake in thyroid cancer diagnosis and therapy, several other methods were explored and used. At the dawn of this new era of recombinant human thyrotropin (TSH) it is of interest to reflect briefly on some of this work. Partially purified bovine TSH (bTSH) was supplied for many years by the Armour Company as Thytropar for intramuscular injection and was first used in thyroid cancer 50 years ago at the Montefiore Hospital and at the Memorial Sloan Kettering Cancer Center in New York City. Most of the patients were already hypothyroid and bTSH induced further 131I uptake in only a few. Experience over the next 30 years revealed frequent allergic reactions, occasionally serious ones, and in 1961 it was shown that prolonged use could result in resistance to both bTSH and human TSH. bTSH was, therefore, reserved for thyroid cancer patients unable to increase endogenous TSH when hypothyroid. bTSH also was used widely as a test to distinguish between hypothyroidism caused by thyroid or pituitary failure until it was replaced by thyrotropin-releasing hormone (TRH). In a few studies, TRH was also tested as an adjuvant to increase endogenous TSH and thus help to stimulate function in thyroid cancer, but this attracted little interest. Prolonged hypothyroidism, enhanced by antithyroid drugs, was used early on, but this very effective stimulant of thyroid cancer function was, for multiple reasons, discarded. Beginning interest 15 to 25 years ago in obtaining TSH from human pituitary glands, a byproduct of growth hormone production, was interrupted when this product was found to risk development of Creutzfeld-Jakob disease. Recombinant human TSH, a safe and effective substitute, is now ready for widespread use and development in thyroid cancer management.