Reversal of the anti-implantation effect of inhibin with progesterone in the hamster.

Inhibin, the gonadal peptide involved in regulation of follicle-stimulating hormone (FSH), exhibited anti-implantation activity in intact and ovariectomized pregnant hamsters. Administration of progesterone reversed the anti-implantation activity of inhibin. Studies were carried out to determine the effect of inhibin on the in vitro synthesis and release of progesterone by the corpora lutea of pregnant hamsters. Inhibin (10 micrograms) was observed to decrease progesterone release by 28%. The administration of exogenous progesterone (2 mg/day) was observed to overcome the anti-implantation effect of inhibin in ovariectomized, pregnant hamsters. These results indicate a possible action of inhibin to interfere with progesterone at the ovarian and/or uterine level in order to exhibit the anti-implantation activity in the hamster.