P11: Spontaneous metritis related to the presence of vaginal septum in pregnant Sprague Dawley rats (CRL:CD(SD)): Impacts on reproductive toxicology studies

Recently, in our facilities, approximately 5% of pregnant Sprague Dawley rats in embryofetal toxicity studies presented abnormal dark uterine contents with generally viable fetuses having a delayed development, at the time of C-section (gestation day 21). In rare cases, a high proportion of the litter was found dead. Macroscopic and microscopic findings consisted of necrosis, hemorrhages and polymorphonuclear cell infiltrates of the placenta associated with bacterial colonies identified as Escherichia coli. In the vagina, similar features were observed associated with mucus accumulation and presence of a transverse occlusive or partially occlusive thin membrane identified as a vaginal septum. Microscopically, this septum consisted of a thin band of vascular connective tissue covered by a mucified epithelium. In some cases, there was only mucus accumulation retained by a septum in the vagina. The presence of these septae most likely caused mucus accumulation and secondary non-specific ascending bacterial infection. We hypothesize that this high incidence of metritis observed in pregnant females may be a consequence of an abnormal number of rats with a vaginal septum. Furthermore, the use of an impedance meter by the breeder to determine the phase of the oestrus cycle could facilitate gestation by causing perforation of the vaginal septum in some cases. The consequences in Reproductive Toxicology studies will be discussed.