Steroid 5-α-reductase (5α-Reductase)

Steroid 5-α-reductase is an oxidoreductase enzyme present in multiple tissues, including the skin, liver, and urogenital tract, responsible for the irreversible conversion of testosterone to dihydrotestosterone (DHT) and other 5-α reduced steroid hormones[2][4][6]. Three isozyme forms are encoded by SRD5A1, SRD5A2, and SRD5A3, differing in tissue distribution and physiological importance[2][4][6]. The enzyme’s activity underpins male sexual differentiation in utero, prostate growth and maintenance after puberty, and the balance of androgenic effects including hair growth and neurosteroid production[3]. Deficiency or inhibition of 5-α-reductase has profound developmental, reproductive, and therapeutic implications, as exploited by drugs such as finasteride and dutasteride in the treatment of BPH and androgenetic alopecia[1][6]. Safety concerns with inhibitors include sexual and reproductive side effects, as well as a contested association with high-grade prostate cancer[1][6].

Other names

3-oxo-5α-steroid 4-dehydrogenase5-alpha reductasesteroid 5α-reductase5AR5 alpha-reductase

Competitive inhibition of 5-α-reductase blocks conversion of testosterone to DHT, reducing androgenic stimulation in target tissues (prostate, hair follicles). Suppression of neurosteroid synthesis in the brain (by some inhibitors).