BIOASSAY OF ANTIGONADOTROPHIC SERA

ABSTRACT Methods are described for the bioassay of the human follicle stimulating hormone (FSH) neutralising potency of antigonadotrophic sera. The methods are based on a modified ovarian weight augmentation test using human chorionic gonadotrophin (HCG) or luteinising hormone (LH) of ovine origin for augmentation. The antigonadotrophic sera were obtained following immunisation of rabbits with HCG, human menopausal gonadotrophin (HMG) and human hypophysial gonadotrophin (HHG) preparations. The FSH neutralising potencies of these antisera were assayed against laboratory standard preparations of HMG and HHG and against the Second International Reference Preparation of HMG. When HCG was used for augmentation, the FSH neutralising potency of antisera depended on the sequence in which HCG, HMG and antiserum were combined. When HCG was mixed with the antiserum prior to the addition of HMG, this resulted in a significant decrease in the FSH neutralising potency. When HCG was injected separately from the HMG-antiserum complex, the FSH neutralising potency increased. However, the FSH neutralising potency of all antisera was significantly higher when LH of ovine origin, rather than HCG was used for augmentation. Anti-HCG sera exhibited a considerable FSH neutralising potency, even when prepared by immunisation with HCG preparations of high specific activity. These high FSH neutralising potencies were in contrast to the low FSH activity of the HCG preparations used for immunisation. Anti-HMG sera possessed little, if any, FSH neutralising potency. These poor FSH neutralising potencies were in contrast to the high FSH activity of the HMG preparations used for immunisation. The FSH neutralising potency of an anti-HHG serum was at least 5 times higher when assayed against HMG, than when assayed against HHG. The data presented indicate that HCG preparations extensively compete with FSH preparations for antibodies neutralising FSH activity. This suggests that there is a cross reaction between HCG and FSH. The data also indicate, that there are significant differences in the antigenic properties of human pituitary and urinary gonadotrophins. It is concluded, that the establishment of specificity of immunoassay methods for human gonadotrophins cannot be based exclusively on immunological evidence. Also, the absorption procedures used to improve the specificity of antigens and antisera are of limited value, unless carried out in a strictly quantitative manner following the establishment of the profile of the gonadotrophic and antigonadotrophic activities present.