BIOASSAY OF ANTIGONADOTROPHIC SERA

ABSTRACT Methods are described for the bioassay of the human chorionic gonadotrophin (HCG) – and luteinising hormone (LH) neutralising potencies of antigonadotrophic sera. The methods are based on the increase in weight of the accessory reproductive organs of intact immature male rats and on the increase in weight of the ventral prostate of hypophysectomised immature rats. The antigonadotrophic sera were obtained following immunisation of rabbits with HCG, human menopausal gonadotrophin (HMG) and human hypophysial gonadotrophin (HHG) preparations. These sera were then assayed against the laboratory standard and the International Standard preparations of HCG, as well as against a highly purified HCG preparation. The antigonadotrophic potencies of the various antisera showed a close agreement, when assayed in intact or hypophysectomised animals against the different HCG preparations. When anti-HCG sera were assayed in intact or hypophysectomised animals against the laboratory standard of HMG, the antigonadotrophic potencies were approximately three times higher than those obtained against HCG preparations. In an attempt to account for this discrepancy, the laboratory standard of HCG was assayed against the laboratory standard of HMG and the Second International Standard preparation of HCG was assayed against the Second International Reference preparation of HMG in both assay systems used. The potency of 1.0 IU of HCG corresponded to that of 2.5 to 2.9 IU of LH. If this difference is taken into consideration, the discrepancy in antigonadotrophic titers disappears. However, when anti-HCG and anti-HHG sera were assayed in intact or hypophysectomised animals against an HHG preparation, the antigonadotrophic potencies were approximately ten times lower than those obtained when the antisera were tested against HCG preparations and ten to thirty times lower than those obtained in the assays conducted against the laboratory standard of HMG. Since these discrepancies in antigonadotrophic titers cannot be explained by differences in the gonadotrophic potency of the preparations used, it is concluded, that major differences exist in the antigenic properties of human gonadotrophins of pituitary – and urinary origin.