Pregnant mare's serum gonadotropin: V. Indomethacin or cortisone and the reversal of antifertility efficacy of pregnant mare's serum gonadotropin.

Pregnant mare's serum gonadotropin (PMSG) of 10 IU on day 5 of pregnancy induced luteal demise and consequently an absolute resorption of fetuses and placentae resulted on day 16 of pregnancy. Simultaneous regimen of PMSG and indomethacin or cortisone was found to be consistently effective in preventing the luteolytic effect of PMSG. The growth of the fetuses, placentae as well as corpora lutea was found to be parallel to controls. Similarly, shortening of the duration of pseudopregnancy to 10--12 days in the bilaterally hysterectomized rat by PMSG and its retaining the normal duration of 18--20 days in the presence of indomethacin tempt us to propose that the PMSG-induced luteolysis is possibly reflected through the release of prostaglandin at the ovarian level.