Binding of Methyltrienolone (R1881) to a Progesterone Receptor-Like Component of Human Prostatic Cytosol

The synthetic steroid methyltrienolone (R1881, 17beta-hydroxy-17alpha-methyl-estra-4,9,11-trien-3-one) binds with high affinity to protein in cytosols prepared from human hyperplastic prostate. R1881 also binds to the androgen receptor of rat prostate and the progesterone receptor of rabbit uterus. Other steroids compete with R1881 for unoccupied binding sites in the human prostatic cytosols in a manner similar to that observed with the rabbit uterine progesterone receptor, rather than the rat prostatic androgen receptor. The progesterone receptor-like binding sites are a feature of the prostatic stroma rather than the epithelium.