Androgen induction of follicular epithelial cell growth is mediated via insulin-like growth factor-I from dermal papilla cells.

Androgen significantly stimulates the proliferation of outer root sheath cells that are cocultured with beard dermal papilla cells without cell contact. The expression of insulin-like growth factor I (IGF-I) mRNA in beard dermal papilla cells was stimulated by androgen and antagonized by cyproterone acetate. Outer root sheath cells did not express mRNA for IGF-I either in the presence or absence of androgen. Both of these two types of cells expressed mRNA for IGF-I receptor and the expression was not affected by androgen. Neutralizing antibody against IGF-I antagonized the stimulatory effect of androgen on the growth of outer root sheath cell cocultured with beard dermal papilla cells. These findings suggest that IGF-I is a candidate for androgen induced hair growth factors.