Comparison of the properties of highly purified equine chorionic gonadotropin isolated from commercial concentrates of pregnant mare serum and endometrial cups

Commercial concentrates of equine chorionic gonadotropin derived from pregnant mare serum and equine endometrial cups were further purified by sulfoethyl-Sephadex C-50 chromatography and gel filtration on columns of Sephacryl S200. Highly purified fractions were obtained from the serum concentrate and from the endometrial cups (serum eCG and cups eCG, respectively). The two preparations were very similar chemically with respect to amino terminal amino acids (phenylalanine and serine), carbohydrate content (38–45%), and amino acid content. The cups eCG had a slightly greater average mobility than serum eCG by disc gel electrophoresis (R_F = 0.37 and 0.32, respectively).Notable differences existed between the preparations in certain assay systems. The cups eCG was shown to be more potent than serum eCG by LH bioassay, LH radioimmunoassay (RIA), equine and calf testes FSH radioreceptor assays (RRA), and a RIA utilizing an antibody generated against cups eCG. In contrast, the serum and cups eCGs appeared comparably active in an equine testes LH RRA and RIA using an antibody to a serum-derived eCG. Ratios of FSH:LH activity for both preparations were consistently less than 1, but varied considerably between different assay systems. Although the preparations exhibited very little FSH activity in receptor assays utilizing equine tissues and equine gonadotropins as radioligands, considerable binding activity was measured in calf and rat testes FSH RRAs.These data confirm that variations in the nature of eCG can be reflected in chemical, biological and immunological differences. Further, the properties of eCG preparations vary depending on the source material used for isolation and the assay systems employed for evaluation.