The male-induced pregnancy block (the Bruce effect) in mice: Re-evaluation of the ability of exogenous progesterone in preventing implantation failure

Abstract

The ability of exogenous progesterone administration to prevent implantation failure in newly inseminated females exposed to alien males for 3 days (from 10.00 hr on day 1 to 10.00 hr on day 4 post coitum) was evaluated. Administration of progesterone, 1 mg/female/day, for 5 days beginning at 10.00 hr on day 1 or at 10.00 hr on day 2 prevented the return of oestrus and induced implantation of blastocysts in alien male-exposed females. Administration of progesterone beginning at 22.00 hr on day 2 was only partially effective in preventing return of oestrus in the male-exposed females; however, the majority of the females which exhibited vaginal oestrus showed implanted embryos. Progesterone injection beginning at 10.00 hr on day 3 or later was totally ineffective in preventing return of oestrus in the females. Administration of progesterone beginning at 10.00 hr or at 22.00 hr on day 3 failed to induce implantation in the male-exposed females which returned to oestrus on day 3; however, the treatment induced implantation in the majority of the females which returned to oestrus on day 4. Progesterone administration beginning at 10.00 hr on day 4 was totally ineffective in inducing implantation in the male-exposed females exhibiting the Bruce effect. The results indicate that administration of progesterone beginning at any time prior to the appearance of oestrus facilitates implantation of blastocysts in male-exposed females; however, progesterone administration beginning after the onset of oestrus is totally ineffective in inducing implantation in females. The results also strongly suggest that in females exhibiting the Bruce effect there is a total loss of blastocysts.