Aim: To investigate the androgen receptor (AR) isoforms and its variability of expression in human and rat prostatic tissues. Methods: Human benign prostatic hyperplasia (BPH) and prostatic cancer tissues were obtained from patients undergoing prostatectomy, and rat ventral prostate was incised 3 days after castration. Forty-one AR-positive BPH specimens, 3 prostatic cancer specimens, and 6 rat prostates were used. After processing at 4 , the tissues were examined by means of high resolution isoelectric focusing (IEF) technique to determine their AR isoforms. Results: From the prostatic specimens, 3 types of AR isoforms were detected with pI values at 6.5, 6.0, and 5.3. In human BPH tissues, 15/41 (36.6%) specimens showed all the three types of isoforms, while 19/41 (46.3%) showed 2 isoforms at various combinations and 7/41 (17.1%), 1 isoform. For the 3 prostatic cancer specimens, one showed 3 isoforms, one, 2 isoforms, and the other failed to show any isoform. All rat prostatic tissues showed 2 isoforms at different combinations. Binding of 3H-dihydrotestosterone (DHT) to the isoforms was inhibited by the addition of l00-fold excess of DHT or testosterone, but not progesterone, oestradiol or diethylstilboestrol. Conclusion: AR isoforms are different in different patients. Although their genesis is not clear, the therapeutic implication of the present observation appears to be interesting, that may help clarifying the individual differences in the response to hormonal therapy

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