Fever in pregnant, parturient, and lactating rats.

Conscious virgin, pregnant, or lactating rats were given intravenous Escherichia coli endotoxin while their temperatures were monitored telemetrically. Virgin females responded to 10-50 micrograms/kg endotoxin with a slight hypothermia, followed by a fever of nearly 2 degrees C magnitude. In pregnant rats given 25 micrograms/kg of the endotoxin, fevers were reduced between 96 h before and 24 h after parturition compared with those seen in virgins or in lactating rats > 24 h postpartum. In the 24-h period before expected time of parturition, no rat developed a fever and the majority of animals became hypothermic; furthermore, in 80% of such animals given 25 micrograms/kg endotoxin, the hypothermia was accompanied by death within 3-15 h. Some mortality and hypothermia were also seen up to 48 h before birth and up to 24 h after birth. No mortality was observed in virgin, pregnant, or lactating rats outside of this time period. We conclude that, around the time of delivery, there is a suppression of fever in the rat and occasional toxic responses to endotoxin.