Human chorionic gonadotropin

Human chorionic gonadotropin (hCG) is a glycoprotein hormone that is synthesised by the syncytiotrophoblast cells of the placenta. The hormone is homologous in structure with human luteinising hormone (hLH) and shares with hLH similar qualitative biological actions on the ovary and the testis (Bishop, Nureddin and Ryan, 1976). Whereas the major function of hLH in women is to act synergistically with FSH to produce ovulation and initiate development of the corpus luteum, the function that hCG appears to serve is to convey a hormonal stimulus from the implanted, fertilised ovum to the corpus luteum which calls forth an augmented production of steroid hormones. Its action in the first few days after fertilisation stimulates secretion of oestrogen and progestins by the corpus luteum to prevent the decline in luteal function that normally occurs in an infertile menstrual cycle (Ross et al., 1970; Vande Wiele et al., 1970). hCG is bound at the same receptors as hLH in the ovary (Kammerman et al., 1972; Gospodarowicz, 1973) and the testis (Catt and Dufau, 1973).