Increased 5 alpha-reductase activity in idiopathic hirsutism.

In vitro, genital skin 5 alpha-reductase activity (5 alpha-RA) was measured in ten hirsute women with normal androgen levels (idiopathic hirsutism [IH]) and in ten hirsute women with elevated androgen levels (polycystic ovary syndrome [PCO]) in order to determine the influence of secreted androgens on 5 alpha-RA. In vitro 5 alpha-RA was assessed by incubations of skin with 14C-testosterone (T) for 2 hours, after which steroids were separated and the radioactivity of dihydrotestosterone (DHT) and 5 alpha-androstane 3 alpha-17 beta-estradiol (3 alpha-diol) in specific eluates were determined. All androgens were normal in IH with the exception of higher levels of 3 alpha-diol glucuronide which were similar to the levels of PCO. The conversion ratio (CR) of T to DHT in IH (17.18% +/- 4.6%) and PCO (17.86% +/- 5.2%) were similar, yet significantly greater than the CR of control subjects (4.48% +/- 0.36% P less than 0.01). The CR of T to 3 alpha-diol in IH (8.00% +/- 1.38%) and PCO (10.36% +/- 1.0%) were similar, yet higher than in control subjects (2.96% +/- 0.32%; P less than 0.05). Serum androgens showed no correlation with 5 alpha-RA, while the CR of T to DHT showed a significant positive correlation with the Ferriman and Gallwey score (r = 0.61; P less than 0.01). The increased 5 alpha-RA in IH appears to be independent of serum androgen levels and is, therefore, an inherent abnormality. The term "idiopathic" is a misnomer, because hirsutism in these patients may be explained on the basis of increased skin 5 alpha-RA.