A quantitative assay for the cytoplasmic androgen receptor using [3H]dihydrotestosterone in the presence of NAD+-nucleosidase.
In prostatic cytosol DHT1 is metabolized to 5 alpha-androstane-3 alpha (or beta), 17 alpha-diols with a half life of 2 h even at 4 degrees C. Thus, [3H]DHT appears to be a poor marker for a quantitative assessment of androgen receptors (AR). Methyltrienolone (R1881) seems to be advantageous as it is not metabolized. However, because of considerable binding to progestin receptors, assays using [3H]R1881 are not specific for AR in tissues containing progestin receptors. We, therefore, developed a specific assay for AR using [3H]DHT (14 nM) as marker, where metabolism of DHT is prevented by pre-incubation with NAD+-nucleosidase. The [3H]DHT-receptor complex is separated from free, SHBG-bound and unspecifically bound [3H]DHT by agar gel electrophoresis. The binding sites of high affinity and low capacity are characterized by suppression with unlabelled R1881 (2 microM) in a parallel assay. Under these conditions DHT and R1881 appear to have the same kinetics of association and dissociation. Weighted non-linear regression analysis of specific binding capacity at various ligand concentrations reveals that in rat prostatic cytosol the affinity of DHT (Kd = 0.405 +/- 0.0839 nM) is significantly higher (P less than 0.01) than that of R1881 (Kd = 1.25 +/- 0.271 nM).
D000818:Animals; D002369:Castration; D002855:Chromatography, Thin Layer; D003593:Cytoplasm / Q000378:metabolism*; D013196:Dihydrotestosterone / Q000378:metabolism*; D004587:Electrophoresis, Agar Gel; D004963:Estrenes / Q000378:metabolism / Q000494:pharmacology; D008024:Ligands; D008297:Male; D015741:Metribolone; D009244:NAD+ Nucleosidase / Q000378:metabolism* / Q000494:pharmacology; D011467:Prostate / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D011944:Receptors, Androgen / Q000378:metabolism*; D011987:Receptors, Steroid / Q000378:metabolism*
D004963:Estrenes; D008024:Ligands; D011944:Receptors, Androgen; D011987:Receptors, Steroid; D013196:Dihydrotestosterone; D015741:Metribolone; D009244:NAD+ Nucleosidase