5-ALPHA-REDUCTASE ACTIVITY IN THE HUMAN HAIR FOLLICLE CONCENTRATES INTHE DERMAL PAPILLA

Hair growth depends on a close interaction of different cell populatio ns of the hair follicle. In certain regions of the body androgens inte rfere with this highly regulated cooperation in a yet poorly understoo d manner. The response of hair follicles to androgens can be categoriz ed as androgen-dependent, e.g. in the beard, androgen-sensitive, e.g. in the frontal scalp of affected individuals, or androgen-independent, e.g. in the occipital scalp. At the target cell level, the balance be tween 5 alpha-reductase, 17 beta-hydroxysteroid-dehydrogenase (17 beta -HSD) and 3 alpha-hydroxysteroid dehydrogenase (3 alpha-HSD) yields me tabolites with different androgenic potential. We examined this target cell-specific androgen metabolism in microdissected intact subunits o f dermal papillae, connective tissue sheaths (CTS) and root sheaths. I n dermal papillae, 5 alpha-reductase predominated with an accumulation of the strong androgen 5 alpha-dihydrotestosterone. The specific acti vity of 5 alpha-reductase in the papillae exceeded those in the other hair follicle compartments by a factor of at least 14 in the scalp (5. 4, 0.4 and 0.1 pmol/h per mm(3) in the papilla, CTS and root respectiv ely and at least 80 in the beard (16.0, 0.2 and 0.4 pmol/h per mm(3) i n the papilla, CTS and root respectively). The root sheath keratinocyt es expressed low 5 alpha-reductase levels, but high 17 beta HSD levels , with androstenedione as the major metabolite. The CTS expressed both 5 alpha-reductase and 17 beta-HSD, resulting in androstenedione, 5 al pha-androsterone and 5 alpha-androstanedione. In the CTS and the root sheath, only minor amounts of 5 alpha-DHT were found. In beard papilla e, the 5 alpha-reductase activity was three times that in the occipita l scalp papillae. These results indicate that the androgen response of hair follicles depends on a differentiated intrafollicular androgen m etabolism and that the dermal papilla might be a primary target in thi s process.