The effect of melatonin on melanocyte functions was studied by incubating whole-skin organ cultures with melatonin, as well as by assessing melatonin positivity in melanocytes versus dendricity and pigmentation, when arrested in the G(2) phase. From this study, it was observed that melatonin positivity is inversely related to the length of UV exposure. Increasing melatonin levels are related to decreasing dendricity and pigment donation during photoresponse in the G(2) phase. Melanocyte melatonin positivity increases with dark incubation and is higher with a pulse of UV exposure after dark incubation with melatonin. This increase is associated with a doubling of melanocyte number after dark incubation and a further doubling upon exposure to a pulse of UV. The melanocytes directly take up melatonin, which results in a marked increase in their numbers. Thus, extreme caution should be exercised when using melatonin as an anticancer drug. This finding also simulates the melanocyte repopulation of the skin with repigmentation during summer in polar animals.
Copyright 2000 S. Karger AG, Basel.