A critical review of gonadotropic activity of pregnant mare serum gonadotropin

The equine placental hormone (eCG), otherwise also referred to as Pregnant Mare Serum Gonadotropin (PMSG, the serum component) is a glycoprotein hormone with the highest content of carbohydrate among the pituitary and placental gonadotropins. Studies have revealed that PMSG acts like Luteinizing Hormone (LH) in mare/horse but exhibits both LH and Follitropin (FSH) like activities in heterologous animal species. PMSG is the most used hormone for induction of super ovulation in a number of animal species like rat, cattle, pigs and even buffaloes. Although cAMP is the established second messenger for both LH and FSH, many actions of FSH and LH are not mediated by cAMP. Further the dual activity of PMSG in heterologous animal species adds complications in interpreting its actions. Recent work from our laboratory demonstrates that ovarian ascorbic acid is depleted by LH (in corpus luteum) but increased by FSH (in growing follicles). The second messenger status in some of these effects of PMSG (as LH and FSH) is not clear yet. Future research on PMSG is also indicated to clarify some of these questions.