[Mechanism of action and peripheral metabolism of androgens in women].
Androgens are steroids with 19 carbon atoms located in the biosynthesis chain between progestives and estrogens. The main androgen is testosterone which is mostly the peripheral interconversion product of delta-4-androstenedione whose origin is mixed, from the ovary and the cortex of the adrenals. Dehydroepi-androsterone essentially comes from the adrenals and is accumulated in the form of a sulfate, the DHEAS, which is one the most concentrated circulating steroid. Although DHEAS only has a slight androgenic activity, the possibility of conversion into testosterone in certain target tissues, especially the skin, makes DHEAS a potential androgen to consider in testing and treating hyperandrogenic conditions. The circulating testosterone is, for the most part, bound to proteins and especially a protein having a strong affinity for testosterone and estradiol, the testosterone estradiol binding-protein (TeBG) or sex steroid binding-protein (SBP). The SBP originating from the liver is under the influence of numerous hormonal and non-hormonal parameters. Androgens decrease the binding ability of SBP, SBP modifies the metabolic clearance of the hormones it binds. Thus, measurement of the free testosterone fraction, not protein-bound, is a better index of the production of testosterone than the measurement of its total concentration. In addition, the fraction which is not bound to the SBP of testosterone is considered as the biologically active fraction, and has a good diagnostic value in the determination of a hyperandrogenic condition. In several target organs, testosterone, under the effect of 5 alpha-reductase, an enzyme whose activity is induced by androgens, is transformed in dihydrotestosterone of DHT which has more binding affinity for androgen receptors.(ABSTRACT TRUNCATED AT 250 WORDS)
Pugeat
M
M
Hospices Civils de Lyon, Laboratoire de la Clinique Endocrinologique, Hôpital de l'Antiquaille.
D000727:Androgen-Binding Protein / Q000378:metabolism*; D000728:Androgens / Q000097:blood / Q000378:metabolism* / Q000502:physiology; D001693:Biological Transport, Active; D005260:Female; D006801:Humans; D011944:Receptors, Androgen / Q000378:metabolism*
D000727:Androgen-Binding Protein; D000728:Androgens; D011944:Receptors, Androgen
Mécanisme d'action et métabolisme périphérique des androgènes chez la femme.