Pregnant mare’s serum gonadotrophin. I. Progesterone or prolactin and the reversal of antifertility efficacy of pregnant mare’s serum gonadotrophin.

The study investigates the impact of pregnant mare’s serum gonadotrophin (PMSG) on the fertility of pregnant rats and the role of hormones progesterone and prolactin in reversing this effect.

Impact of PMSG on pregnancy

• The research started with the administration of PMSG to pregnant rats. This hormone caused a complete resorption of the foetuses and placentae in these animals.
• This was linked to the onset of a polyfollicular ovarian state, characterised by multiple ovarian follicles. This condition typically leads to an abnormal secretion of hormones, potentially disrupting processes such as ovulation and pregnancy.
• The dosage of PMSG applied was consistent, of 10 international units (IU), and it was given on the 5th day of the rats’ pregnancies.

Role of Progesterone and Prolactin in Counteracting PMSG

• The researchers then explored the effects of progesterone and prolactin, two key hormones involved in pregnancy, when administered alongside PMSG.
• They found that these hormones could mitigate the effects of PMSG, thereby restoring normal pregnancy conditions.
• This essentially suggests that the combination of PMSG with either of these hormones helps maintain the endocrine balance necessary for the continuity of pregnancy.

Possible Mechanisms

• The study postulates that the luteolytic effects of PMSG (i.e., its capacity to breakdown the corpus luteum) could be due to the hormone’s ability to induce ovarian polyfolliculogenesis (the development of many follicles in the ovaries).
• The corpus luteum is an important part of pregnancy as it secretes the hormone progesterone, essential for maintaining gestation.
• Therefore, the breakdown of the corpus luteum – potentially caused by PMSG – can disrupt hormone secretion and negatively impact pregnancy, a process seemingly reversible through the additional administration of progesterone or prolactin.