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

summary 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.