Induction of anagen in telogen mouse skin by topical application of FK506, a potent immunosuppressant.

The effect of topical application of FK506 on the normal hair cycle of C57BL/6J mice was investigated. When telogen mice (7 weeks of age) were treated topically with 1 mumol FK506 on days 0 and 3, 50% of the tested mice entered anagen by day 9 and 100% by day 16. With 0.1 mumol of FK506, 50% of the tested mice entered anagen by day 13 and 80% by day 19, indicating that the effect of FK506 is dose dependent. In control mice, a spontaneous shift from telogen to anagen started on day 14, and 30% of the control animals were in anagen at day 19. Histologic studies revealed that FK506 markedly stimulated the skin and thickened it. The depth and size of hair follicles were also markedly increased in FK506-treated skin compared to control skin. The data on hair growth also support the contention that FK506 induces early onset of anagen and stimulates hair growth. The hair growth stimulated by FK506 looked normal and the hairs were of normal length. The hair growth was restricted to the site of application. These results clearly demonstrate that topical application of FK506 induces anagen hair growth in telogen mouse skin and indicate that the hair-growth-stimulating effect of FK506 is due at least in part to its promoting effect on the hair cycle.