Immunohistochemical studies of the estrogen receptor alpha in the ovaries and uteri of the domestic cat at different stages of the oestrous cycle

Expression of the estrogen receptor alpha (ER alpha) was investigated in domestic cat ovaries and uteri by mean of immunohistochemistry, using monoclonal antibody against ER alpha. The stages of the oestrous cycle were determined by vaginal cytology and serum steroid levels which were taken before operation. In the uterus, positive staining was found in the nuclei of all uterine cell types in different proportions and staining intensity. During oestrous, the staining intensity and the proportion of positive cells were highest in the epithelium (both the surface epithelium and the glandular epithelium) as well as in the myometrium. At dioestrous, ER alpha expression was clearly low in the surface epithelium and myometrium but not in the germinal epithelium. During anoestrous, weak staining as well as low proportion of positive cells was observed in most of the compartments of the uterus, apart from the stroma, the proportion and the intensity of positive cells was not markedly different during all stages of the oestrous cycle. In the ovary, positive staining was only found in some ovarian cells. During oestrous, strong staining was seen in the germinal epithelium and in the stroma of the ovaries. Additionally, faint staining was also observed in some luteal cells. However, no positive staining of Era ws detected in other ovarian samples collected at the other stages. In conclusion, the study showed that estrogen elicits its function mainly via ER alpha in al uterine cell types. In the ovary, the observation that not all ovarian cell types express ER alpha could suggest that the estrogen receptor, subtype alpha, is neither the major nor the only protein that causes estrogen to elicit its effect the role of the estrogen receptor, subtype beta (ER beta), should be further clarified in this respect.