170 Endocrine controls of hair growth: New Developments

Ralf Paus, Dept. of Dermatology, University Hospital Eppendorf, University of Hamburg, Hamburg, Germany

While the significance of androgens as major modulators of hair growth is well-established, much less is known on the exact follicular functions of other nuclear hormone receptor ligands (e.g. endogenous estrogens, thyroid hormones, retinoids, calcitriols, glucocorticoids) and on non-steroidal, peptide hormones and neuropeptides (e.g. ACTH, aMSH, CRH, prolactin, substance P, catecholamines, melatonin). This introductory synthesis begins by summarizing important relevant findings from the old endocrine literature (mostly in rodents) that serve to highlight many of the most intriguing open questions on the hormonal controls of hair growth, both in an endocrine and in a paracrine/autocrine signalling context, which the overly dominant androgenocentric view of the hair follicle has tended to obscure. This is followed by a discussion of more recent findings that document the hair follicle to be both a source and a target of numerous hormones, neuropeptides and neurotransmitters, whose expression (along with that of their cognate receptors) underlies tight, hair cycle-dependent regulatory controls. In particular, the hypotheses are explored that the hair follicle exploits several locally generated and/or metabolized hormones for controlling its own growth, innervation, immune functions, perfusion and/or pigmentation and that the hair follicle has established a miniature equivalent of the hypothalamic-pituitary-adrenal axis, possibly as part of a complex, local stress response-system.