5alpha-Androstan-17beta-ol-3-one

5alpha-Androstan-17beta-ol-3-one, also referred to as androstanolone or dihydrotestosterone, is an anabolic androgenic steroid. 5alpha-Androstan-17beta-ol-3-one is converted from testosterone by 5alpha-reductase type 2, which reduces the 4,5-double bond of testosterone, in genital skin and prostate. It plays an important role in the testis and muscle, and is crucial for the development, function and pathology of the prostate. Relative to testosterone, 5alpha-Androstan-17beta-ol-3-one is considerably more potent as an agonist of the androgen receptor (AR) and is in fact the most potent known endogenous ligand of the receptor. It has an affinity (Kd) of 0.25 to 0.5nM for the human AR, which is about 2- to 3-fold higher than that of testosterone (Kd = 0.4 to 1.0nM) and 10-fold higher potency of inducing androgen receptor signaling. In addition, unlike testosterone, 5alpha-Androstan-17beta-ol-3-one is inactivated by 3alpha-hydroxysteroid dehydrogenase (3alpha-HSD) into the very weak androgen 3alpha-androstanediol in various tissues such as muscle, adipose and liver among others. In relation to this, 5alpha-Androstan-17beta-ol-3-one has been reported to be a very poor anabolic agent when administered exogenously as a medication.