Hair growth-modulation by adrenergic drugs

Since We have recently shown that the Pz-adrenoreceptor (beta(2)-AR) expres sion of selected regions of the hair follicle (HF) epithelium as well as th e number of adrenergic nerve fibers in murine skin change in a hair cycle-d ependent manner, this has raised the possibility that adrenergic nerves may exert "trophic" functions during HF cycling. To further explore this conce pt, we have investigated the effect of neuro-pharmacological manipulations on hair growth (anagen) induction in quiescent telogen mouse skin in vivo. Hen, we demonstrate that subcutaneous injections of the noradrenaline (NA)- depleting agent guanethidine, or of the neurotoxin 6-hydroxydopamine, but n ot of the beta(2)-AR agonist isoproterenol induce a premature onset of anag en in the lower back skin of C57BL/6 mice. On day 20 after the start of tre atment, more than 80% of the guanethidine-treated mice and ca. 65% of the 6 -hydroxydopamine-treated (6-OHDA) mice exhibited premature skin darkening a nd hair growth at the site of drug application, whereas less than one-third of all control animals showed macroscopic signs of anagen development. Thi s was confirmed by histology, demonstrating mature anagen VI HFs only at th e immediate site of treatment with guanethidine or 6-OHDA as opposed to res ting telogen HFs in the neighboring untreated skin area. This observation f urther supports the concept that sympathetic nerves are intimately involved in hair growth control and invites one to explore the neuro-pharmacologica l manipulation of piloneural interactions as a novel therapeutic strategy f or the management of hair growth disorders.