Thyroid-stimulating activity of chorionic gonadotropin and luteinizing hormone

Area of Science:

• Endocrinology
• Reproductive Biology
• Thyroid Research

Background:

• Human chorionic gonadotropin (hCG) is known to have thyroid-stimulating activity (TSA).
• The presence of other thyrotropic molecules in hCG preparations has been a subject of investigation.
• Understanding the source of TSA in hCG is crucial for interpreting its physiological roles.

Purpose of the Study:

• To determine if thyrotropic factors other than hCG are present in hCG preparations.
• To investigate whether TSA is an intrinsic property of the hCG molecule.
• To assess the thyrotropic activity of luteinizing hormone (LH) due to structural similarities with hCG.

Main Methods:

• Comparing the ratio of interstitial cell-stimulating activity (ICSA) to TSA in crude and purified hCG.
• Gel filtration of purified hCG to separate protein fractions.
• Assessing TSA in a hybrid LH molecule created from recombined subunits.

Main Results:

• The ratio of ICSA to TSA remained consistent during hCG purification.
• TSA and ICSA co-eluted in all fractions after gel filtration of hCG.
• A hybrid LH molecule exhibited significant TSA beyond expected TSH contamination.

Conclusions:

• The data strongly suggest that TSA is an intrinsic property of the hCG molecule.
• No evidence supports the existence of a separate thyrotropic factor in hCG preparations.
• The findings support the hypothesis that structurally similar hormones like LH may also possess intrinsic TSA.