hCG-INDUCED TSH RECEPTOR ACTIVATION AND GROWTH ACCELERATION IN FRTL-5 THYROID CELLS

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Abstract
Our previous studies have indicated specificity cross-over between LH/hCG and the TSH receptor. We have now analyzed the ability of the TSH-dependent Fisher Rat thyroid cell line (FRTL-5) to proliferate in a differentiated state under the influence of highly purified hCG (hCG-CR121). TSH receptor activation and growth induction were observed after 7 days suspension from a TSH-induced growth phase. The effect of 10 .mu.g hCG-CR121 was equivalent to 500 .+-. 43 (mean .+-. SEM) uIU of human TSH (2nd IRP, 80/558) with reference to growth stimulation, as judged by 72-h [3H]-thymidine uptake and to approximately 15 .+-. 35 uIU human TSH with reference to receptor activation as judged by cyclic AMP accumulation. These data demonstrate specificity cross-over by hCG for the TSH-dependent FRTL-5 cell line and suggest that hCG has greater growth-stimulating than thyroid-stimulating potential when compared with human TSH.