The male-induced implantation failure (the Bruce effect) in mice: effect of exogenous progesterone on maintenance of pregnancy in male-exposed females.

Abstract

The effect of exogenous progesterone given early during pregnancy in maintaining pregnancy in alien male-exposed mice was investigated. Administration of progesterone, 1 mg/female/day, on days 1 to 5 post coitum was fully effective and on day 2 to 6 post coitum was partially effective in maintaining pregnancy in females. However, progesterone injection on days 3 to 7 post coitum was totally ineffective in maintaining pregnancy in females. The results suggest that only when administration of progesterone is begun early during male exposure, luteal failure in newly inseminated females is prevented. The results also suggest that failure of corpus luteum function or some other irreversible changes leading to luteolysis occur in females early during exposure to alien males before the external manifestation of implantation failure (vaginal cornification). It is suggested that exogenous progesterone given early during alien male exposure prevents luteal failure and maintains pregnancy in females through its facilitatory effect on hypophysial prolactin secretion.