Development of rat prostatitis model by oral administration of isoflavone and its characteristics

Inflammation of the prostate can be induced experimentally in rats by the s ubcutaneous administration of estrogen. However, it is usually achieved at the price of some alteration in the sex steroid hormone balance and morphol ogical changes in the prostate. In this study, a soy-extracted isoflavone m ixture with weak estrogenic activity was administered orally in an attempt to induce prostatitis in a more physiologic way and to characterize the inf lammation induced. A total of 36 male Sprague-Dawley rats, 8 weeks old, were divided into 2 gr oups. The control group was fed with only an AIN-76A diet containing no det ectable phytoestrogen and the experimental group was fed with AIN-76A and a soy-extracted isoflavone mixture (genistein 60.0% and daidzein 19.6%), 300 mg/kg body weight for 9 weeks. The sequential body weight and prostate weig ht at necropsy were measured. A histologic examination and histomorphometry assessed the changes in the prostate. The serum concentrations of testoste rone and dihydrotestosterone were measured to estimate the effects on the a ndrogen level. Intraprostatic concentrations of genistein and daidzein were measured by gas chromatography/mass spectroscopy (GC/MS). While no sign of prostate inflammation was apparent in the control group, s evere inflammatory changes in the stroma, increased epithelial detachment a nd inflammatory exudates within the glandular lumen of the dorsolateral pro state were observed in more than 80% (15/18) of the experimental group. How ever, there was no significant difference in the ventral prostate between t he two groups. The daidzein and genistein concentrations in both the latera l and ventral prostates were significantly higher in the experimental group than in the control group where no isoflavone was detectable. In addition, the concentrations were much higher in the dorsolateral than in the ventra l prostate. Although the body weight gain was not consistent in the experim ental group, there were no significant differences in the prostate weight a nd serum androgen level between groups. In summary, when a soy-extracted genistein and daidzein-rich isoflavone mix ture was administered orally into rats, prostatic inflammation with charact eristic lobe specificity developed. The present method of inducing prostati tis seems to be a more physiologic than an estrogen-induced experimental mo del, and sequential pharmacokinetic studies might help in establishing this model as a more valuable toot in assisting future research in this field.