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Human Chorionic Gonadotropin Stimulates Iodide Uptake, Adenylate Cyclase, and Deoxribonucleic Acid Synthesis in Cultured Rat Thyroid Cells^*

Endocrine Research Laboratory, Wadsworth Veterans Aministration Medical Center, and University of California School of Medicine Los Angeles, California 90073

Address requests for reprints to: Jerome M. Hershman, M.D., Endocrinology- Wll ID, Wadsworth Veterans Administration Medical Center, Los Angeles, California 90073.

hCG stimulates thyroid function, but it has been suggested that it is impurities in commercial hCG preparations or a variant of hCG that are responsible for the thyrotropic activity. In this study, we tested the thyrotropic activity of purified and commercial hCG and compared its action with that of bovine TSH (bTSH) in cultured rat FRTL-5 cells in regard to stimulation of iodide uptake, activation of adenylate cyclase, and synthesis of DNA. Iodide uptake was measured after incubation of the cells for 48–72 h with the test hormones, followed by a 40-min incubation with 0.1 µCi Na¹²⁵I and 10 µmol/L carrier Nal; the ¹²⁵I in the washed cells was counted. Adenylate cyclase was measured after incubation of the cells with the test stimulators for 3 h in hypotonic medium by RIA of cAMP in the medium. DNA synthesis was measured after incubation of the cells with the test substances for 24 h, followed by addition of [³H]thymidine for 3 h and then measuring the incorporation of [³H]thymidine into the cells.

Both purified and commercial hCG produced a dose-related increase in iodide uptake. The relative potency of commercial hCG was 0.024 µU bTSH/U hCG and that of purified hCG was 0.042 µU bTSH/U hCG; compared with human TSH, the potency of purified hCG was 0.72 µU/U hCG. hCG caused a doserelated increment of adenylate cyclase and [³H]thymidine incorporation. The effect of hCG on iodide uptake and [³H]thymidine incorporation was additive with that of bTSH; hCG was not an antagonist of TSH in these cultured rat thyroid cells. We conclude that hCG has intrinsic thyrotropic activity in FRTL-5 cells in regard to stimulation of iodide uptake, activation of adenylate cyclase, and stimulation of DNA synthesis.

^* This work was supported by V.A. Medical Research Funds. Published in preliminary form in Clin Res 35:182A, 1987.

Received November 11, 1987.

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