O#01   Biological Effects of Androgens on the Hair Follicle :Experimental Approaches

Valerie A. Randall. Dept of Biomedical Sciences, University of Bradford, Bradford, UK

Androgens have strong influences on human hair growth. Generally there are little effects in other mammals, with a few noticeable exceptions such as the neck manes of male lions and red deer. In people, the effects of androgens are paradoxically different depending on the body site. Androgens stimulate tiny vellus follicles producing short, thin, virtually colourless hairs to enlarge to terminal follicles making longer, thicker and frequently darker hairs. This occurs during puberty in both sexes in the axilla and pubis, clearly separating children and adults. In men, the higher levels of androgens also promote terminal hair growth on the face and other regions including the chest, upper pubic triangle and limbs. Since this clearly distinguishes the sexually mature adult male, excess hair growth in women (hirsutism) causes psychological distress. The opposite response occurs on the scalp where androgens inhibit the terminal hair growth causing progressive balding (androgenetic alopecia). This occurs commonly in a defined pattern in men depending on their genetic background. In women, the situation is more complex and frequently a general thinning on the vertex occurs. Since human hair is so involved in social communication, androgenetic alopecia causes significant reduction in the quality of life. These factors make the study of androgens in human hair growth a difficult area. Like other hormones, androgens act via specific cellular receptors in their target tissues, therefore their actions must be studied in follicles which are regulated by androgens. This eliminates investigations in many mammals, particularly most laboratory rodents. In addition, it means that appropriate specific follicles or skin areas need to be studied to assess androgen action. Specialised animal models such as the balding stumptailed macaque or the androchronogenetic mouse can be used for androgenetic alopecia and red deer stag mane for androgen-stimulated follicles. Although some of our understanding of androgen action comes from observing the effects of genetic mutations, e.g. 5a-reductase type II, or hormonally-manipulated individuals, human basic science studies are by necessity focussed on in vitro models. In these, comparison of androgen-regulated follicles or their components with control, non-balding scalp follicles is an appropriate, though difficult approach. The advent of molecular biological techniques promises to facilitate further understanding of the complex action of androgens on hair growth.