Sex hormones and modulators of the genital system.

PMSG is a potent gonadotrophin, with dual FSH and LH activity. It is composed of two non-covalently associated alpha and beta subunits, and is heavily glycosylated on its CTP tail. This extensive glycosylation is of key importance for obtaining the extended half life in blood typical of PMSG. As PMSG binds to FSH and LH receptors, it stimulates follicular growth and follicular maturation during the days preceding oestrus and ovulation. Limited amounts of PMSG will result in induction and synchronization of ovulation in cattle and small ruminants, irrespective of their cyclicity prior to treatment. Administration of slightly higher amounts will modestly increase ovulation rate and litter size. Administration of high amounts of PMSG will result in superovulation, therefore resulting in the numerous blastocysts needed for embryo transfer. PMSG also has the potential to induce puberty in swine.

The pharmacokinetic profile observed following injection of PMSG is characterized by the very long half life generated by the high glycosylation (N and O glycosylations) of the PMSG molecule. It also explains why a single PMSG administration has the ability to support follicular growth throughout the full duration of the follicular phase (2 to 5 days long according to the species).

Absorption of PMSG is rapid: In all three species studied, following injection, PMSG is rapidly absorbed from the injection site and C max is reached by 8 (pig/sheep) or 16h (cattle) following injection. Bioavailability following i.m. injection (compared to i.v. administration) is high in all species (cattle: 72%, pig: 71.3%, sheep: 92.6%).

PMSG elimination is slow: The elimination half life has been shown to range between 34 and 150 hours according to the species.