Finasteride is a well-known inhibitor of the prostatic enzyme 5α-reductase type 2 which prevents conversion of testosterone into 5α-dihydrotestosterone, the active intraprostatic androgen, which causes prostate involution through a combination of cell atrophy and cell death. The drug is widely used to improve symptoms of benign prostatic hyperplasia in man. Clusterin, a glycoprotein which is generally up-regulated under conditions inducing cell atrophy or organ involution, is produced at a high level in the regressing rat ventral prostate following androgen ablation. According to several authors, clusterin does not respond to finasteride treatment, suggesting a different action of testosterone and 5α-dihydrotestosterone. We show here that, under our conditions, finasteride was capable of inducing production of both clusterin mRNA and protein in the rat ventral prostate. In fact, by using different and converging techniques, such as Northern hybridization, in situ hybridization histochemistry and immunohistochemistry, we were able to show a strong induction of the clusterin gene in the epithelial cell population of the gland. The response to finasteride, which was similar to that seen with castration, occurred with a delay of a few days. In situ and immunohistochemistry experiments indicated that both orchidectomy and finasteride administration resulted in increased transition of the epithelial cells from the columnar to the cuboidal (atrophic) shape, and this was accompanied by an increased intensity of the signal for clusterin. Thus, it appears that induction of clusterin is part of the molecular process leading to prostate involution caused by either orchidectomy or finasteride administration
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