Six choriocarcinoma cell lines that secrete chorionic gonadotropin (hCG) in tissue culture were investigated for the production of thyroid stimulators. In the mouse thyrotropin bioassay, no thyroid-stimulating activity was found in cell culture media even after 30-fold concentration by the method of Bates. Further, concentrates of culture media did not react in a porcine thyrotropin radioimmunoassay in which hCT cross-reacted completely. Thyroid function was also assessed in hamsters bearing hCG-secreting human choriocarinoma transplants. Even though the thyroid-stimulating factor present in commercial urinary hCG preparations caused an increase in PB131I in the hamster, the presence of the choriocarcinoma had no effect on PB131I. From these results, it appears that human choriocarcinoma cell lines maintained in tissue culture and human choriocarcinoma serially transplanted in the hamster are not suitable models for the study of the secretion of a thyroid-stimulating factor by trophoblastic tissues.
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