4-Nitrophenol induces Leydig cells hyperplasia, which may contribute to the differential modulation of the androgen receptor and estrogen receptor-α and -β expression in male rat testes

• PNP disrupted estradiol-to-testosterone balance.
• PNP induced hyperplasia of Leydig cells and reduction of aromatase expression.
• PNP differentially modulated AR, ER-α and -β expression in male rat testes.

4-Nitrophenol (PNP) is generally regarded as an environmental endocrine disruptor capable of estrogenic and anti-androgenic activities. To investigate PNP-induced reproductive effects, immature male rats were injected subcutaneously with PNP (0.1, 1, 10 mg/kg body weight or vehicle) daily for 4 weeks. We assessed reproductive tract alterations, sex hormone balance in the serum and estrogen receptor (ER)-α, -β and androgen receptor (AR) expression in testes. Although no significant difference was observed in body weight or testes weights of PNP-treated rats compared with the controls, the serum concentrations of testosterone in the 10 mg/kg PNP-treated group were significantly elevated. This effect was accompanied by Leydig cells hyperplasia in the testes. Conversely, there was a significant decrease in estradiol concentration and aromatase expression in the testes of the 10 mg/kg PNP-treated group. Furthermore, we observed a significant increase in ERα expression in the testes of the 10 mg/kg PNP-treated group compared with the control group. Conversely, ERβ expression displayed a significant reduction. Moreover, AR expression was significantly increased in the 10 mg/kg PNP-treated group compared with the control group. The existence of AR, ER-α and -β in the testes suggests that estradiol and testosterone directly affect germ cells and that differential modulation of AR, ER-α and -β in the testis may be involved in the direct effects of PNP or either the indirect effects of PNP-induced disruption of the estradiol-to-testosterone balance or the Leydig cells hyperplasia. Thus, the measurement of many endpoints is necessary for good risk assessment.