Progesterone levels and socially-induced implantation failure and fetal resorption in golden hamsters (Mesocricetus auratus).

Levels of circulating progesterone (P) were significantly reduced in socially subordinate female golden hamsters following brief exposures to another female. Reduced P levels were accompanied by an increased incidence of implantation failure when social interactions occurred on days 2-4 after mating and by increased fetal mortality when interactions occurred later during pregnancy (days 5-7 or 10-12). P levels, the incidence of implantation failure and rate of fetal resorption were highly correlated with the number of attacks and chases sustained by subordinate females. Smaller reductions in plasma P levels and marginally significant decreases in fecundity were also noted among dominant animals and among females paired with unfamiliar males later in pregnancy. The fact that these effects occurred even with relatively brief exposure periods suggests that they could occur in the wild.