α-MSH causes a small rise in cAMP but has no effect on basal or ultraviolet-stimulated melanogenesis in human melanocytes

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Abstract
The effects of α-melanocyte stimulating hormone (α-MSH) were studied on levels of cyclic adenosine 3′,5′-monophosphate (cAMP), melanin content and response to ultraviolet radiation (UVR) in cultured human melanocytes (HuMC). ForeskinHuMC were cultured in a hormone-supplemented system not dependent on the presence of phorbol esters. Following addition of α-MSH (10-6m) there was a rise in cAMP levels maximal between 5 and 15 min to 9.4±3.2 pm/ 105 cells, while control levels were 3.6±0.7pm/105 cells. After 7 days’culture in the presence of ±-MSH (10-8-10-6m) the melanin content increased by only 35%, whereas Forskolin (10-5m) induced a 9.5-fold rise in cAMP after 5 min and a 10.9-fold rise in melanin content after 7 days. When HuMC were irradiated daily for 6 days with UVR (Helarium fluorescent lamps emitting 20% UVB, 80% UVA) melanin content rose 2.7-fold (SE0.3). This was unchanged or slightly reduced in the presence of α-MSH (10-8-10-6m). Parallel observations on Cloudman S91 melanoma cells showed that α-MSH caused only an 80% increase in melanin content after 4 days. The rise in melanin content induced by three daily UV-irradiations (2.4-fold, SE0.5) was unchanged by α-MSH (10-8-10-6m). Although α-MSH induces a small rise in cAMP in HuMC this does not result in melanogenesis, and the response to UVR is not affected by α-MSH in either HuMC or S91 cells.