Extraction and characterization of a thyrotropic material from the human placenta

A material with thyrotropic activity was extracted from fresh human placentas. After chromatography of the extract on carboxymethyl cellulose, thyroid-stimulating activity ranged from 0.12 to 1.06 mU of thyroid-stimulating hormone (TSH) per mg of protein in bioassays of eight preparations. The amount of TSH per placenta varied from 113 to 2200 mU and approximated the content of the pituitary gland. Additional purification by gel filtration on Sephadex G-100 gave a maximum activity of 8 mU/mg. The most active portion was eluted in the same position as (125)I-labeled bovine or human TSH, a fact suggesting that the molecular size of this thyrotropic substance was similar to that of pituitary TSH. Another placental fraction with weaker activity was eluted earlier indicating that the placental material was heterogeneous. In the McKenzie mouse bioassy, the response of the placental thyrotropin paralleled that of the beef TSH standard. There was no long-acting thyroid stimulator effect. Antibodies to both human and bovine pituitary TSH neutralized the biologic activity of the placental TSH. Placental thyrotropin cross-reacted very weakly in a sensitive radioimmunoassay for human pituitary TSH; it cross-reacted completely in a radioimmunoassay for bovine pituitary TSH, and this assay was used for following the purification. The role of this thyrotropic material as a possible cause of thyroid hypertrophy and hyperfunction in pregnancy and in patients with trophoblastic tumors remains to be investigated.