VPT 311: General and Systemic Veterinary Pharmacology (2+1)

PLACENTAL GONADROTROPHINS

• The maintenance of the corpus leuteum of pregnancy in some species is favoured by the production of chorionic gonadotropin (CG) eg. human (hCG) from day 8
• in the mare the endomaterial cups produce a hormone (eCG) from day 40 to about day 150 (previously called pregnant mare serum gonadotropin (PMSG)).
• hCG contains more of LH than FSH, while eCG contains more of FSH than LH.
• hCG is mainly leutienising. In female animals this induces ovulation and reinforces the secretion of progesterone by the ovary.

Effects

• hCG will bind to LH receptors on the granulos, theca and luteal cells with high affinity and specificity.
• eCG has LH like activity only in the mare, but in the other species it has mainly FSH like activity.
• In the mare it only leutinize follicles already present in the ovary but, in the other species it stimulates follicular growth and ovulation.
• Serum gonadotrophin has been used to increase the number of developing follicle and ovulation and oestrus and thus increase the incidence of twins in cattle.

Uses

It is used to control the time of ovulation in mares because in these animals ovulation normally occurs towards the end of a long estral period.
• It is widely used in the treatment of cystic ovarian disease especially where nymphomania is present and sometimes in the treatment of cyrptorchidism.
• In male animals chorionic gonadotropin is used to stimulate the secretion of testosterone by the testes.