Research articleExpression of oxytocin, progesterone, and estrogen receptors in the reproductive tract of bitches with pyometra

Canine pyometra is considered a serious and life-threatening condition. Due to the relationship among sex steroid hormones, oxytocin receptor (OTR) expression, and canine pyometra pathogenesis, this study aimed to investigate the expression of oxytocin, progesterone, and estrogen receptors in the reproductive tissues of canines with pyometra by real-time PCR and immunohistochemistry. A total of 27 pyometra bitches were classified into open- and closed-cervix pyometra groups based on the presence of vaginal discharge. Moreover, 15 normal bitches in the luteal phase served as a control group. The results showed that OTR gene expression in the ovary of pyometra bitches was higher than that of normal bitches, whereas the level of OTR gene expression in the cervix of pyometra bitches was less than that of normal bitches (P < 0.05). Conversely, a lower OTR H-score in ovarian follicles was observed in pyometra bitches compared with normal bitches, whereas a higher percentage of OTR-positive immunostaining in uteri and cervices were found in pyometra bitches compared with normal bitches (P < 0.05). Moreover, the H-scores of estrogen receptor alpha in uteri and cervices of pyometra bitches were less than that of normal bitches (P < 0.05). However, the localization of the OTR and sex steroid receptors between groups of pyometra bitches was not different. Our findings suggest that pyometra pathogenesis is associated with a change in expression of OTR and sex steroid receptors in the canine reproductive tract. However, cervical dilation in bitches with pyometra was not influenced by the expression of OTR and sex steroid receptors.