Abstract

PIP: Pregnant mare's serum gonadotropin (PMSG) 10 IU was injected in rats on Day 5 of pregnancy. Counting of implanted blastocysts was done on Day 8 of pregnancy through a midventral incision. The corpora lutea were noted to be significantly smaller (p less than .001) than controls. Autopsies were done on Day 16 of pregnancy. In some rats, clomiphene citrate (Clomid) was used as an antiestrogenic in a dose of .3 mg/kg injected sc on Days 5, 7, and 9. In others, reserpine was injected sc in a dose of .5 mg/kg on Days 5, 7, 9, 11, and 13 of pregnancy. The single injection of PMSG resulted in complete resorption of fetuses and placentae by Day 16. The Clomid reversed the antifertility action of PMSG and maintained growth of fetuses, placentae, and corpora lutea with 100% fetal survival. It is assumed that excessive luteinizing hormone (LH), as induced by the PMSG, stimulates ovarian estrogen. Since reserpine initiates prolactin release and inhibits LH release, the direct antagonism of prolactin at the luteal level may take place by inhibiting the enzyme activity of 20alpha-hydroxysteroid dehydrogenase.