Steroid 5alpha-reductases and 3alpha-hydroxysteroid dehydrogenases: key enzymes in androgen metabolism

Best Pract Res Clin Endocrinol Metab. 2001 Mar;15(1):79-94. doi: 10.1053/beem.2001.0120.


Androgen action in mammals can be regulated at the pre-receptor level by the intracellular formation and degradation of potent androgens, such as 5alpha-dihydrotestosterone (5alpha-DHT). In androgen target tissues (e.g. prostate), 5alpha-DHT is formed from circulating testosterone by the action of the type 2 steroid 5alpha-reductase (5alpha-R) and its action is terminated by the action of a reductive 3alpha-hydroxysteroid dehydrogenase (3alpha-HSD) which forms the weak androgen 3alpha-androstanediol. Oxidative 3alpha-HSD isoforms, however, can provide an alternative source of potent androgens by converting 3alpha-androstanediol to 5alpha-DHT. Working in concert, 5alpha-Rs and 3alpha-HSDs determine the amount and the type of androgen available for the androgen receptor and hence affect transcription of genes under androgen control. In peripheral tissues (e.g. liver), type 1 5alpha-R and reductive 3alpha-HSD isoforms work consecutively to eliminate androgens and protect against hormone excess. Thus, different 5alpha-R and 3alpha-HSD isoforms participate in distinct anabolic and catabolic processes and their important roles in androgen action render them drug targets for the treatment of androgen-dependent diseases.

Publication types

  • Research Support, U.S. Gov't, P.H.S.
  • Review

MeSH terms

  • 3-Hydroxysteroid Dehydrogenases / metabolism*
  • 3-Oxo-5-alpha-Steroid 4-Dehydrogenase / metabolism*
  • 3-alpha-Hydroxysteroid Dehydrogenase (B-Specific)
  • Androgens / metabolism*
  • Animals
  • Humans


  • Androgens
  • 3-Hydroxysteroid Dehydrogenases
  • 3-alpha-Hydroxysteroid Dehydrogenase (B-Specific)
  • 3-Oxo-5-alpha-Steroid 4-Dehydrogenase