Comparative Binding Specificity of Methyltrienolone in Human and Rat Prostate

Abstract

The binding of methyltrienolone (R 1881) in crude human hyperplastic prostate cytosol was determined by a charcoal assay. Maximum binding was observed after 2–3 h of incubation at 0 °C. This binding decreased steadily thereafter and reached 41% of the 2-hour values after 96 h of incubation. In human hyperplastic prostate, the binding of ³H-R 1881 was competed by low concentrations of R 1881, R 5020 and progesterone and by high concentrations of dihydrotestosterone (DHT) and 17α-methyl-DHT. In the rat prostate, on the other hand, this binding was competed by low concentrations of DHT and 17α-methyl-DHT and only by high concentrations of progesterone and R 5020. The apparent association constant (Ka) of R 1881 was determined in three human prostates and found to be 0.2–0.4 X 10⁹ liters/mol; the number of binding sites ranged from 101 to 158 fmol per mg of protein. These findings constitute further evidence for the existence of relatively large amounts of a progesterone-binding component in human hyperplastic prostate.