THE MALE-INDUCED IMPLANTATION FAILURE (THE BRUCE EFFECT) IN MICE - EFFECT OF EXOGENOUS PROGESTERONE ON MAINTENANCE OF PREGNANCY IN MALE-EXPOSED FEMALES

The effect of exogenous progesterone given early during pregnancy in m aintaining pregnancy in alien male-exposed mice was investigated. Admi nistration of progesterone, 1 mg/female/day, on days 1 to 5 post coitu m was fully effective and on day 2 to 6 post coitum was partially effe ctive in maintaining pregnancy in females. However, progesterone injec tion on days 3 to 7 post coitum was totally ineffective in maintaining pregnancy in females. The results suggest that only when administrati on of progesterone is begun early during male exposure, luteal failure in newly inseminated females is prevented. The results also suggest t hat failure of corpus luteum function or some other irreversible chang es leading to luteolysis occur in females early during exposure to ali en males before the external manifestation of implantation failure (va ginal cornification). It is suggested that exogenous progesterone give n early during alien male exposure prevents luteal failure and maintai ns pregnancy in females through its facilitatory effect on hypophysial prolactin secretion.