Human Chorionic Gonadotropin — A Hormone Secreted for Many Reasons

Human chorionic gonadotropin, a glycoprotein hormone secreted in large quantities by the placenta, normally circulates at readily detectable levels only during gestation. It shares a common quaternary structure of two dissimilar subunits (designated alpha and beta) with the pituitary glycoprotein hormones luteinizing hormone, follicle-stimulating hormone and thyroid-stimulating hormone. Although the amino-acid sequences of the alpha subunits of the human glycoprotein hormones are essentially identical, those of the beta subunits differ and account for the unique immunologic and biologic activities of each glycoprotein hormone.1 Although luteinizing hormone and human chorionic gonadotropin have biologic activities in common, reflecting the 80 per cent . . .