[Hormonal interaction and hair growth]

Androgenetic alopecia (AGA) is the most common form of hair loss in men and women. This continuous process results in a form of alopecia that follows a definite pattern in those individuals who are genetically predisposed. Although clinically different, the pathogenetic pathways leading to this type of hair loss are thought to be similar in both sexes. A genetic predisposition is a feature of AGA, but the predisposing genes are still unknown. Our understanding, however, of the hormonal effects on hair growth is far more advanced. AGA can be defined as a dihydrotestosterone (DHT)-dependent process with continuous miniaturization of sensitive hair follicles. So far, we do not understand the molecular steps involved in androgen-dependent beard growth versus androgen-dependent hair loss. However, the local androgen metabolism plays a central role in the intrafollicular conversion of weak androgens, such as DHEAS, to more potent androgens such as T or DHT within the hair follicle. The dermal papilla plays a central role by exhibiting an array of important steroidogenic isoenzymes. Provided that the dermal papilla (DP) cell triggers and regulates the growth of hair follicles, this physiological role may be reflected by metabolic differences, which could account for differences in androgen sensitivity as observed in hair follicles from different body sites, and in conditions such as male pattern baldness. The observation of STS, 17beta-HSD, 3beta-HSD, 3alpha-HSD and type 2 5alpha-R-activity within the DP could be a clue to understanding the regulation of androgen action in the human hair follicle by local androgen modification on target cell level. Hence, some of the intrafollicular steroidogenic enzymes would be potential pharmaceutical targets for the treatment of AGA or hirsutism.