Thyroid-Stimulating Activity and Chorionic Gonadotropin

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Abstract

The nature of the substance with thyroid-stimulating activity (TSA) present in human chorionic gonadotropin (hCG) prepared from pregnancy urine was investigated. In the mouse thyrotropin bioassay, the characteristic maximum of blood radioactivity obtained with the TSA in hCG preparations occurred after that obtained with pituitary thyrotropin (hTSH) but before that obtained with long-acting thyroid stimulator. Antiserum to the α subunit of hCG produced significant neutralization of the TSA in hCG. Significant antagonism of hTSH biologic activity was achieved with certain doses of hCG, suggesting that the TSA in hCG was a partial agonist of hTSH. This antagonism was neutralized by antiserum to the β subunit of hCG. These immunologic results suggest that the substance with TSA in hCG preparations contains antigenic determinants similar to those of both the α and the β subunit of hCG. Amounts of highly purified hCG and crude commercial hCG of equal immunologic activity were biologically indistinguishable in the bioassay for TSA. Both hCG immunoreactivity and the TSA in hCG adsorbed to concanavalin A and eluted with 0.2 M methyl α-D-glucopyranoside. These results are consistent with the hypothesis that TSA is an intrinsic property of hCG or of a glycoprotein molecule physicochemically, biologically, and immunologically similar to hCG.

Authors

Bruce C. Nisula, Jean-Marie Ketelslegers