Failure of stressful stimuli to inhibit embryo implantation in the rat

Psychogenic pregnancy disruptions in mammals

Evidence scattered over the literatures of zoology, psychology, agricultural science, and medicine indicates that diverse stressors will interfere with pregnancy in its early stages. It is probable that the most sensitive period is around the point of intrauterine implantation of fertilized ova. Although there is some indication that conventional "stress" hormones of the pituitary-adrenal axis can inhibit implantation, this evidence is too weak and inconsistent to suggest that these hormones are primary mediators of early pregnancy disruptions. Increasingly, evidence indicates that the balance of ovarian steroids is most important for pregnancy maintenance. It is well known that minute amounts of exogenous estrogens can completely disrupt pregnancy, and some new evidence suggests that endogenous estrogens may be released from the adrenals and/or ovaries during psychological stress.

Effect of predator exposure upon early pregnancy in mice

Female CD-1 and C57 mice were inseminated according to standard procedures and randomly assigned to varied treatments in the first trimester of pregnancy. In the first experiment, mice housed for one week with preselected nonassaultive rats produced very few litters in contrast to controls. In the second experiment, this same effect was observed when inseminated mice were separated from the rat by a wire grid. In the third experiment, inseminated mice were exposed daily to saline or the urine of male or female rats in their home cage bedding. Fewer females exposed to rat urine of either sex produced litters.