[Androgen binding proteins in the rat prostate: methodological problems and regulation (author's transl)].

Protamine sulfate precipitation is used for the selective and quantitative assay of equilibrium binding constants. The association constant of dihydrotestosterone is 1 X 10(9)1/mole and the number of binding sites is 11.500/cell. The affinity of testosterone is slightly lower than that of dihydrotestosterone, whereas some synthetic androgens have a higher affinity in accordance with their biological activity. Estradiol, progesterone and antiandrogens can displace dihydrotestosterone from its receptor. The occupied cytosolic and nuclear binding sites can be measured by radioimmunoassay. After castration, the nuclear hormone-receptor complexes disappear with a half-life of 3 hours. The cytosol receptor decreases steadily between the first and the fourth day after castration, then increases spontaneously. Testosterone seems to inhibit the degradation and also to stimulate the synthesis of its own receptor. Radioautography shows that the receptor is present only in the epithelial cells.