Characterization and measurement of the androgen receptor in human benign prostatic hyperplasia and prostatic carcinoma

[6,7- ³H]Methyltrienolone (R 1881) has been used as ligand to measure and characterize the androgen receptor in human benign prostatic hyperplasia and prostatic carcinoma. [ ³H]R 1881 was bound with high affinity and low capacity to cytosol from 6 out of 9 specimens of transvesically enucleated benign prostatic hyperplasia and from 2 specimens of prostate carcinoma obtained by Veenema biopsy or transvesical enucleation. The dissociation constant of the [ ³H]R 1881 receptor complex was in the range of 0.3-1.8 x 10 ^-M and the number of binding sites 9-26 fmoles/mg protein. [ ³H]R 1881 was displaced from its binding sites on the receptor by 5α-dihydrotestosterone and testosterone; much less efficient competitors were LS 1727, cyproterone acetate, 17β-estradiol, R 5020, 5α-androstane-3α, 17β-diol and progesterone, whereas 4-androstene-3, 17-dione, cyproterone, estramustine and cortisol did not compete. The receptor was stable at 0 C but was degraded rapidly (t 1/2 = 14 min) at 37 C. The rate of dissociation of the [ ³H]R 1881-receptor complex increased at higher temperatures (t 1/2 = 810 and 50 min at 0 C and 37 C, respectively). The [ ³H]R 1881-receptor complex had an isoelectric point of about pH 5. 5α-[ ³H]Dihydrotestosterone was found to be an unsuitable ligand in assays of the androgen receptor in benign prostatic hyperplasia since this steroid also binds to testosterone-binding globulin that probably contaminates all prostate cytosol preparations. Furthermore, 5α-[ ³H]dihydrotestosterone was rapidly metabolized in prostate cytosol, even at 0 C, whereas [ ³H]R 1881 was not. Electroresected specimens did not contain detectable levels of androgen receptor, probably due to heat denaturation.