Changes in serum hormone levels associated with male-induced ovulation in group-housed adult female mice.

Endocrine changes mediating male-induced estrus were examined in intact female mice which were rendered pseudopregnant by housing in groups. Adult female mice were placed in group cages on the day of estrus, and on day 5 of the ensuing pseudopregnancy, a mature male mouse was placed in the group cage. Animals were killed and serum levels of LH, FSH, PRL, estradiol, and progesterone were assayed over the 72 h after introduction of the male. During the first 24 h of male exposure, progesterone plummeted to basal levels. These events were followed by a gradual rise in serum estradiol, an increase in uterine weight, and an LH surge at 62 h which was followed by ovulation. PRL levels tended to be lower in treated females, but this was not significant. It is postulated that the initial exercise of the male is to destroy the corpus luteum of pseudopregnancy,presumably by suppressing luteal support. The question is raised of whether the male is also necessary to induce the subsequent LH surge or if suppression of the corpus luteum is sufficient for estrus to result.