Biomedical subjects
Publications and source records attributed to B C Nisula.
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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.
Concanavalin-A covalently linked to Sepharose was used to extract the glycoproteins from a volume of human plasma about 10 times that volume usually added to conventional radioimmunoassay systems. Using a chorionic gonadoptropin (hCG) radioimmunoassay, hCG inhibition curves generated in the presence of the extracts were nearly identical to those generated by the conventional method; therefore, the sensitivity of the radioimmunoassays for glycoprotein hormones.
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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 alpha 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 beta subunit of hCG. These immunologic results suggest that the substance with TSA in hCG preparations contains antigenic determinants similar to those of both the alpha and the beta 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 alpha-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.
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To assess the in vivo steroidogenic activity of desialylated human choriogonadotropin (hCG) in man, highly purified desialylated hCG was administered as a constant intravenous infusion over 6 hours to four normal men at a rate sufficient to maintain substantial levels of desialylated hCG in the serum. The mean percent change of serum testosterone from baseline during the first 6 hours in men given an infusion of desialylated hCG was compared to that in saline-infused controls and that in men given highly purified intact hCG. The mean change of serum testosterone at 6 hours in the group infused with desialylated hCG (129% of baseline) was significantly greater than that of the controls (69% of baseline). Furthermore, the response to desialylated hCG could not be distinguished from that of hCG (125% of baseline). It was concluded that desialylated hCG, when given as a constant intravenous infusion, can elicit a substantial serum testosterone response comparable to that seen with purified hCG, and thus, that desialylated hCG behaves as an agonist of the LH/CG receptors on human Leydig cells.