Post-tyrosinase inhibition of melanogenesis by melatonin in hair follicles in vitro.

In short-term (48 hr) culture hair follicles of the Siberian hamster retain both tyrosinase activity and the capacity to produce melanin. The addition of melatonin to such cultures at concentrations between 10-6 M and 10-10 M brings about a dose-related inhibition of melanogenesis but tyrosinase activity is unaffected. The use of a series of melatonin analogues and blockers suggests that the hair follicle melanocytes possess melatonin receptors, although their location remains to be determined. Melatonin also inhibits the increase in melanogenesis brought about by alpha-melanocyte-stimulating hormone (MSH) but again it has no effect upon the increased levels of tyrosinase which accompany this MSH response. It is suggested that melatonin inhibits melanogenesis through a mechanism which operates at some post-tyrosinase step in the melanin biosynthetic pathway.