HAIR-GROWTH INDUCTION BY SUBSTANCE-P

BACKGROUND: lit vitro, some neuropeptides, including the tachykinin, s ubstance P (SP), act as growth factors. The cyclic growth of the richl y innervated hair follicle offers a model for probing such functions i n a complex, developmentally regulated tissue interaction system under physiologic conditions. Dissecting the role of neuropeptides in this system may also reveal as yet obscure neural mechanisms of hair growth control. EXPERIMENTAL DESIGN: The neuropeptide-releasing neurotoxin, capsaicin was injected intradermally, or SP slow-release formulations were implanted subcutaneously in the back skin of C57BL/6 mice with al l follicles in the resting stage of the hair cycle (telogen) in order to see whether this induced hair growth (anagen). In addition, the end ogenous SP skin concentration and the activity of the main SP-degradin g enzyme, neutral endopeptidase, were determined during the induced mu rine hair cycle by high performance liquid chromatography-controlled r adioimmunoassay (SP) or by fluorometry (neutral endopeptidase). RESULT S: Both capsaicin and SP induced significant hair growth (anagen) in t he back skin of telogen mice. This was associated with substantial mas t cell degranulation. The endogenous SP skin concentration showed sign ificant, hair cycle-dependent fluctuations during the induced murine h air cycle, which were largely independent of the activity of neutral e ndopeptidase. CONCLUSIONS: SP may play a role in the neural control of hair growth. Whereas this pilot study does not address the underlying mechanisms of action, it demonstrates that SP has potential as a hair growth-stimulatory agent in vivo, and serves as a basis for exploring the role of tachykinins in epithelial-mesenchymal-neuroectodermal int eraction systems like the hair follicle.