3-Alpha-Hydroxysteroid Dehydrogenase (HSD3a)

3α-HSD catalyzes the inactivation of androgens in the prostate by converting 5α-dihydrotestosterone to 3α-androstanediol, where excess 5α-dihydrotestosterone is implicated in prostate disease. Ascheme for the actions of androgen, progestin, and glucocorticoids involving the participation of 3a-HSD is proposed.

According to this scheme, in the mechanism of steroid action 3a-HSD not only regulates the concentration of the main effector androgen, 5a-dihydrotestosterone, in target cells, but also switches androgen, progestin, and glucocorticosteroid genomic activity to non-genomic activity. The human lung is known to have a high level of 17β-HSD and 3α-HSD activity. 3α-HSD activity with 5α-DHT of microsomes from normal, adult lung was particularly susceptible to inhibition by coumestrol.