Effect of the estrous cycle on uterine infection induced by Escherichia coli

Escherichia coli was inoculated into the uterine lumen of rats and rabbits at different estrous stages; one uterine horn of each animal was ligated at the cervical end. In rats, a large number of E. coli were retained in the ligated horns regardless of the estrous stage. E. coli inoculated at diestrus or pseudopregnancy induced purulent endometritis, but when inoculated at proestrus-estrus the organism caused asymptomatic infection. In nonligated horns, few E. coli were recovered, and marked histopathological changes were not observed. Large numbers of E. coli were retained in the nonligated horn at proestrus as a result of physiological constriction of the cervix. E. coli inoculated at proestrus never caused purulent endometritis in either the ligated horn or the nonligated horn. In rabbits, E. coli infused into ligated horns brought about purulent inflammation irrespective of ovarian states. The number of recoverable E. coli was reduced rapidly at the follicular phase as compared with the luteal phase. These results suggest that the stage of the estrous cycle when animals are inoculated with E. coli influences the course of the uterine infection.