Stimulation of follicular melanogenesis in the mouse by topical and injected melanotropins

The effects of melanocyte-stimulating hormone (α-MSH) and related analogs on follicular melanogenesis in the mouse (C57BL/6JA^γ) were studied. [Nle⁴, D-Phe⁷]-α-MSH and the related fragment analogues Ac-[Nle⁴, D-Phe⁷]-α-MSH_4-11-NH₂ and Ac-[Nle⁴, D-Phe⁷]-α-MSH_4-10-NH₂, stimulated the conversion of pheomelanogenesis to eumelanogenesis when subcutaneously injected at concentrations 100-fold lower than the native hormone, α-MSH. In addition, the melanotropin analogs stimulated follicular eumelanogenesis when applied topically to the skin of mice. The melanotropins were transdermally delivered to the systemic circulation as evidenced by the fact that eumelanogenesis was stimulated in hair follicles in areas distant from the site of topical application. These results demonstrate that peptide hormone analogs can be transported across the skin. The unique actions of the melanotropin analogs may relate to the fact that these peptides are nonbiodegradable and thus exert prolonged actions on melanocytes. These compounds may prove important for studies on normal integumental melanogenesis and for the treatment of hypopigmentary disorders in humans.