Pregnant mare’s serum gonadotropin. IV. Induction of premature labor by pregnant mare’s serum gonadotropin and its prevention by using clomiphene or indomethacin.

The research investigates the effect of pregnant mare’s serum gonadotropin (PMSG) on inducing premature labor in pregnant rats, and the potential ways to prevent it. Substances like progesterone, clomiphene, and indomethacin were studied for their role in inhibiting the abortifacient effects of PMSG, leading to the suggestion that PMSG functions through the release of prostaglandin stimulated by estrogen.

Investigating the Role of PMSG in Inducing Premature Labor

• The study began by experimenting with the effects of the administration of pregnant mare’s serum gonadotropin (PMSG) on pregnant rats.
• PMSG, given in doses of 30 IU on the 18th day of the rats’ pregnancy, was found to result in premature labor.

The Mediating Role of Other Drugs on PMSG’s Effects

• The study then tested whether a simultaneous injection of certain other drugs – specifically progesterone, clomiphene, or indomethacin – could prevent the premature labor induced by PMSG.
• Remarkably, the premature labor did not occur when any one of these three substances was injected along with PMSG.
• This led the researchers to propose that the action of PMSG might be mediated by the release of prostaglandin, which is stimulated by estrogen.

Influence of Uterus absence on PMSG-induced premature labor

• The research additionally tested the effects of PMSG on pseudopregnant rats that had undergone bilateral hysterectomy (removal of the uterus).
• PMSG was found to terminate the pseudopregnancy of these rats, but this termination could be reversed by indomethacin.
• This discovery led to the conclusion that the inhibition of luteal function (a critical part of the menstrual cycle and pregnancy) by PMSG does not require the presence of a uterus.