Chronic stress increases estrogen and other steroids in inseminated rats.

Physical restraint, like many other stressors, can block early pregnancy, but the underlying physiological mechanisms have not been established. Exogenous estrogens in minute doses will also block early pregnancy. In the present study, female rats were exposed to 5 h of restraint daily for the first 5 days after insemination. A subset of animals was sacrificed after 1, 2, 3, 4, and 5 days of restraint, and blood was collected for radioimmunoassay. Blood was also collected from unstressed control animals on each of the first 5 days after insemination. Plasma concentrations of estradiol, as well as those of corticosterone and progesterone, were increased in the stressed animals as compared to the controls. The finding of significantly enhanced maternal estrogen suggests the possibility that estrogens mediate psychogenic pregnancy blocks.