[Inhibition of nidation in mice by modification of the environment and pheromones. Re-establishment by prolactin and thioproperazine].

325 mated mice (evidence of a vaginal plug, J1) were divided into 8 groups, 246 were subjected to various kinds of stress before day 7 of gestation: 120 were placed singly in boxes and/or transferred to different ones: 75 were exposed to alien males with or without box transfer. 85% of the 50 unstressed females did, in fact, become pregnant. Isolation by itself did not modify the course of gestation. Transfer to a new box (74 females) along with isolation from days, 1, 2, 3 or 4 on reduced the percentage of pregnant females to 55%. Exposure to a strange male in the common box of females (26 females) reduced it to 55%. Isolation of a single female with a strange male, along with transfer (49 females; Bruce Effect) on day 4, 5 or 6 reduced this percentage to 25, 6 or 20% respectively. In addition when the stress occurred on day 4 the number of implantations was greatly reduced. A daily s. c. injection of B prolactin or of thioproperazine on days 4, 5 and 6 prevented the onset of the pregnancy block (47 females). If the 325 mice are separated into 2 groups, those ind whom gestation was maintained and those who aborted, ponderal growth greatly increased in the former; their adrenal glands weighed less, and their preputial glands weighed more. An excessive secretion of corticosteroids in non-pregnant females could be the cause of the inhibition of prolactin release. These results suggest that the effects and probably the implicated mechanisms are the same for pheromones and environmental changes as prolactin and thioproperazine prevent the effects in both cases. The variation in the susceptibility of mice could be due to genetic factors that play a primary role in hypophyso-adrenal response to emotional stress.