Abstract

PIP: A radioreceptor assay for 5alpha-dihydrotestosterone (DHT) which uses castrated rat ventral prostate cytosol receptor and either charcoal dextran or polyethylene glycol to separate unbound steroid is described. Optimal amounts of charcoal (25%), polyethylene glycol (10%), stability of the receptor, and time after castration were determined to perfect the assay. The cytosol receptor bound tritiated DHT, which was displaced by unlabeled DHT in a dose-response relationship, with either method of separation. Testosterone competed for the receptor, but was one-third as potent. Other active substances were: 4-androstene-3beta, 17beta-diol, 5-androsten-3beta, 17beta-diol, 5alpha-androstane-3beta,17beta-diol, 5alpha-androstane-3alpha,17beta-dio l and 5 alpha-androstane-3,17-dione. Binding was not inhibited by estradiol, dehydroepiandrosterone, 4-androsten-3,17-dione, progesterone, cortisol, 3beta-hydroxy-5alpha-androstan-17-one, or clomiphene citrate. Since 4 androstene-3,17-dione and dehydroepiandrosterone are 15 and 12.6% as potent androgens and DHT in vivo, but were inactive in this assay, they are probably metabolized to active androgens in vivo. The stereospecificity for binding and for androgenic effect of the other steroids are discussed.