Immunolocalization of sex steroid hormone receptors in canine vaginal and vulvar tissue and their relation to sex steroid hormone concentrations.

The aim of this immunohistochemical study was to describe the cellular distribution of the estrogen receptor-alpha (ERalpha), progesterone receptor (PR) and androgen receptor (AR) in canine vaginal and vulvar tissue. Samples were taken from dogs in different stages of the estrous cycle. Nuclear staining for ERalpha, PR and AR was observed in surface epithelium, stromal and smooth muscle cells. Receptors were also expressed in vulvar skin. Cytoplasmic staining for AR was observed in basal and parabasal cell layers of vulvar and vaginal epithelium. For all three receptors, staining intensity was generally higher in stromal cells compared with epithelial cells, suggesting that stromal cells may be more receptive to steroid hormone action. Therefore, as in other tissues of the female genital tract, stromal-epithelial interactions induced by sex steroid hormones may be of importance in canine vaginal and vulvar tissues. No cyclic changes in receptor immunostaining were observed. Significant positive correlations were found between receptor immunostaining in some vaginal and vulvar cell groups and the serum concentrations of estradiol-17beta and testosterone, but not with the serum progesterone concentration. Significant negative correlations were found between ERalpha immunostaining in epithelial and stromal cells of the vagina and the serum estradiol-17beta concentration, suggesting a negative feedback mechanism between estradiol-17beta and its receptor. Both cell types play a role in the differentiation of vaginal epithelium, under the influence of estradiol-17beta.