Expression Pattern of Markers in the Canine Ovarian Cycle

Although hormonal changes during different phases of the oestrous cycle of bitches are well-described, knowledge about the luteal phase and anoestrus is incomplete. Furthermore, which paracrine and autocrine critical factors that differentiate between follicles destined for atresia and those that continue to develop are unknown. In this study, ovarian tissue was collected from 39 healthy bitches that were subject to ovariectomy or ovariohysterectomy for surgical neutering or medical purposes such as unwanted pregnancy. Bitches were allocated to different groups depending on the stage of the oestrous cycle. Serum progesterone, LH, FSH and 17β-estradiol (E₂) -levels were determined and immunhistochemistry was performed for a variety of receptor antigens; Ki-67, vimentin, pan cytokeratin antibody, p53 and oestrogen receptor (ER) α antigens. Marked differences were found in progesterone concentration between pregnant and non-pregnant animals. Oestrogen concentration was significantly lower in pro-oestrus and ovulation than during the luteal phase. Although progesterone could be detected in cytoplasm of ovarian cells at each stage, its presence was restricted to follicular cells during anoestrus. A strong presence of AE1/AE3, vimentin and p53 was found in each oestrous stage, in contrast with Ki67. The localization of ERα appeared to vary during the oestrous cycle, a phenomenon that suggests a switch between target cells of oestrogen; while as a proliferation marker, the mild reaction of p53 during parturition suggests an apoptotic process at this stage of the cycle.