Androgen receptor expression in the testes and epididymides of prenatal and postnatal Sprague-Dawley rats.

The androgen receptor (AR) plays a critical role in sexual differentiation and in the virilization of the male reproductive system. A clear understanding of AR expression at the early stages of sexual development will help elucidate the sensitivity of perinatal animals to endocrine modulation by external agents, such as some environmental chemicals. Immunohistochemistry was used in this study to localize the AR in the differentiating testis and epididymis of Sprague-Dawley rats starting from gestation day 15 until postnatal day 21. Positive AR staining was found on gestation day 15 in the mesenchymal as well as in the epithelial cells in the mesonephros. Weak staining was also observed in a small number of interstitial cells in the primordial testis at this age. The fetal interstitial and peritubular myoid cells showed positive AR immunoreactivity early in development, but the Sertoli cells did not overtly express the receptors until postnatal day 5. The intensity of staining and number of AR-positive cells in the testis and epididymis increased over time. The epithelium in the mesonephros-derived tissues, including rete testis and epididymis, appeared to exhibit a higher capacity to express AR than the rest of the testicular tissue. The results demonstrate that AR expression in the primordial male reproductive system is highly specific to time and cell type and modify previous understanding on the timing of AR expression in the testicular tissue. Since AR-positive cells at various developmental stages may be potential sites of interaction with chemicals that adversely affect sexual differentiation, improved understanding of AR ontogeny will help in investigating the effects of AR-reactive agents, such as environmental antiandrogens, with respect to specific windows of sensitivity.