Objective  To establish an experimental prostatitis animal model in Sprague-Dawley (SD) rats through induction by treatment of estrogen and androgen at different concentrations.

  Methods  Fifty-three male SD rats aged 3 to 4 months were used in the study, and the castration model of male rats was established by excision of bilateral testes. The rats were randomly assigned to a blank group, a castration group and treatment groups receiving estrogen and androgen at different concentrations after castration, with 4 rats in each group. Dihydrotestosterone (DHT) and estradiol (E) were administered daily by subcutaneous injection to the treatment groups. All the rats were sacrificed by way of cervical dislocation after 1 month and the serum DHT and E concentrations of the rats in each group were assessed with ELISA. Prostate specimens were collected and the relative weight of the prostate of each group of rats was calculated. After HE staining of the prostate tissue, we observed with optic microscope structural changes in the prostate tissue and the state of prostatic inflammation in each group. Immunohistochemical examination was done to assess the expression of three inflammatory factors, transforming growth factor-β1 (TGF-β1), interleukin (IL)-6 and IL-8, in rat prostate tissues.

  Results  The results of HE staining of rat prostate tissue showed that, compared with the blank group and castration group, the degree of inflammation increased significantly in the E0.05+DHT 0.5 mg/kg group and DHT0.15+E0.15 mg/kg group (P<0.05). However, once the concentration of DHT exceeded 0.5 mg/kg, the degree of inflammation did not further aggravate. The results of immunohistochemical staining showed that when the concentration of exogenous E was constant, the expression of TGF-β1 and IL-8 increased significantly in the E0.05+DHT 0.15 mg/kg group, E0.05+DHT 0.5 mg/kg group and E0.05+DHT 1.5 mg/kg group compared with that of the blank group (P<0.05). In the E0.05+DHT 0.15 mg/kg group and E0.05+DHT 0.5 mg/kg group, the expression of TGF-β1 and IL-8 increased significantly compared with that of the castration group (P<0.05). Once the concentration of DHT reached 0.5 mg/kg, further increase in the concentration of DHT did not lead to any significant changes in the expression of TGF-β1 or IL-8. In addition, when the concentration of exogenous DHT remained unchanged, the expressions of TGF-β1, IL-6, and IL-8 increased significantly in the DHT0.15+E 0.05 mg/kg group and DHT0.15+E 0.5 mg/kg group, compared with that of the blank group and castration group (P<0.05).

  Conclusion  Castration combined with treatment of different concentrations of estrogen and androgen could successfully induce the prostatitis model in SD rats.