New Evidence for Intrinsic Follicle-Stimulating Hormone-Like Activity in Human Chorionic Gonadotropin and Luteinizing Hormone*

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Abstract
In order to investigate whether the follicle-stimulating activity (FSA) of purified human CG [chorionic gonadotropin] (hCG) is an intrinsic property of the hCG molecule or reflects contamination with FSH of pituitary origin, the FSH-like effects of a series of hCG preparations were measured in an FSH radioligand-receptor assay (RRA). Preparations included crude and highly purified hCG, isolated hCG.alpha. or hCG.beta. subunits, and the hCG subunits recombined either with each other or with purified ovine LH.alpha. or ovine LH.beta. subunits. FSH-like activity in the RRA was based on the ability of test preparations to inhibit specific binding of radiolabeled FSH to rat testis homogenate. To examine for the presence of contaminating pituitary FSH, the FSH-like activity of several of the preparations was measured in the FSH RRA after incubation with a specific antiserum to ovine FSH. Purified hCG had 0.10-0.15% the potency of highly purified hFSH in the FSH RRA. Recombined hCG.alpha. plus .beta. was essentially indistinguishable from purified native hCG, although the isolated subunits had virtually no FSH-like activity. Similar to purified hCG, the hybrid recombinants HCG.alpha.oLH.beta. and oLH.alpha.CG.beta. also had FSH-like activity. Although an excess of the FSH antiserum neutralized over 94% of the activity of a pituitary hFSH preparation in the FSH RRA, it failed to neutralize the FSH-like activity of hCG, hCG.alpha.oLH.beta., or oLH.alpha.hCG.beta.. The FSH-like effects of highly purified hCG and hCG-oLH hybrid preparations were not due to pituitary FSH contamination. The FSH-like effects of purified hCG preparations are due to an interaction of the intact hCG molecule with the FSH receptor. LH.beta.-containing hybrids also possess an intrinsic FSH-like action.