Immunohistochemical localization of estrogen receptor-alpha in sex ducts and gonads of newborn piglets

Estrogen receptor-alpha (ER-alpha) expression in piglet uteri has previousl y been reported from day 15 after birth. Nevertheless, uterine tissue has b een reported to be estrogen sensitive from the day of birth. Since estrogen action in the uterine tissue is suggested to be mediated principally by ER -alpha, the present study aimed to evaluate the presence of ER-alpha in ute ri of 1- to 2-day-old piglets by means of immunohistochemistry. In addition , sex ducts and gonads of both sexes were examined. The results clearly dem onstrate the presence of ER-alpha immunopositive cells in uterine tissue, w hich explains its estrogen responsiveness. Immunostaining was most intense in the glandular epithelial cells and is suggested to indicate participatio n of ER-alpha in adenogenesis. In oviducts, almost all epithelial cells wer e immunostained moderately positive, while the stroma cells were stained co mparably more positive. The functional significance of this intensity diffe rence is uncertain but could indicate that part of the estrogen action on t he epithelium is mediated through the stroma cells, as is known for the ute rus. In ovaries, the surface epithelium and stroma cells were immunostained , whereas germ and granulosa cells were immunonegative. It is speculated th at ER-alpha might be involved in yet unknown intraovarian mechanisms. In ma le sex ducts, immunostaining was virtually confined to the epithelium of ef ferent ducts. All cells in the epididymis as well as in vas deferens were i mmunonegative. The unique presence of ER-alpha in efferent ducts correspond s with localization in other species, where it has been shown to be involve d in fluid reabsorption. The obtained data on localization of ER-alpha corr espond with the present knowledge, obtained in ER-alpha knockout mice. of t he biological function of ER-alpha within male and female gonads and sex du cts.