GONADOTROPIN BIOASSAYS IN THE CONTEXT OF DUAL ACTIVE PREGNANT MARE SERUM GONADOTROPIN (PMSG): A REVIEW

The bioassays for the pituitary gonadotropins have been discussed with regard to specificity, sensitivity, precision and accuracy. Bioassays were in vivo assays to begin with but later became in vitro biochemical assays and still later only Receptor binding assays. To a large extent bioassays have been replaced by immuno assays which are more sensitive. However immuno assays sometimes measure biologically inactive isoforms/fragments/modified forms of active hormones. Placental gonadotropins like human chorionic gonadotropin (hCG) and Pregnant mare serum gonadotropin (PMSG) otherwise called as equine chorionic gonadotropin (eCG) exhibit dual activities. PMSG has both FSH-like and LH-like biological activities in heterologous animal species while hCG exhibits both LH-like and Thyrotropin (TSH) like activity. Bioassays are required for monitoring purification of these hormones from tissue extracts. The structural basis of this immunological and biological cross reaction in assays is understood in the case of hCG vis-à-vis human pituitary LH and TSH. However in the case of mare, we are far from understanding the structural basis for the dual activity of PMSG. Bioassays for FSH and LH activity measurement using mice have been standardized in our laboratory and the same have been used to investigate the dual activity of PMSG.