RESUMEN
OBJECTIVE: To investigate the estrogenic activity of para-nonylphenol in immature SD rats and explore the mechanism and sensitive indicators of its action in uterotrophic assay. METHODS: The vehicle control (peanut oil), positive control(estradiol benzoate, E2B, 0.4 mg/kg) and p-NP(60 mg/kg, 90 mg/kg and 120 mg/kg) were given orally (by gavage) q.d. on the 21st, 22nd, 23rd postnatal days. Then the rats were sacrificed 24 hours after the last administration. By using ABC immunohistochemistry, the progesterone receptor (PR), estrogen receptor (ER), and proliferating cell nuclear antigen (PCNA) of the rat uterine were analysed. RESULTS: Uterine weight, uterine/body weight significantly increased in E2B 0.4 mg/kg, p-NP 90 mg/kg and 120 mg/kg groups as compared with those of vehicle control group (P < 0.01), and a dose-response relationship was observed. The expressions of PR, ER and PCNA in the nuclei of stromal and myometrial cells of uterus were detected in all the p-NP groups, and a dose-effect relationship was noted. CONCLUSION: Expressions of PR, ER and PCNA as indicators tested by immunohistochemical technique are more sensitive than uterine weight in uterotrophic assay. Hyperplasia of stromal and myometrial cells of uterus is the reason why the uterine weight of the rat increased.