The open and closure of cervical canal is an important function in both reproductive physiological and pathological processes. The cervical dilation during the estrous cycle is involved the presence of oxytocin receptor (OTR) in most species. The regulation of cervical dilation during the estrous cycle in bitch has not been exactly reported. This study aimed to investigate the expression of OTR in bitch cervical tissue during various stages of the estrous cycle using immunohistochemical technique. Thirty-one bitches were divided into three groups, follicular, luteal, and inactive phase according to ovarian structures. The results presented as the mean percentage of the positive staining area showed that the OTR expression was mostly found in the cytoplasm of all cervical compartments. The highest percentage of OTR positive staining area was observed in the follicular phase group (P<0.05), whereas the lowest OTR expression was observed in the inactive phase group (P<0.05). The present study suggested that the OTR expression is influenced by the phase of the estrous cycle and that cervical cells are the target sites of oxytocin during the estrous cycle. Therefore it may also conclude that the action of oxytocin may play a role in the mechanism of the cervical dilation in cyclic bitches through the expression of its receptor.

Key words: Bitch, Cervix, Immunohistochemistry, Oxytocin receptor