NLE(4)DPHE(7)ALPHA-MELANOCYTE-STIMULATING HORMONE INCREASES THE EUMELANIN-PHEOMELANIN RATIO IN CULTURED HUMAN MELANOCYTES

In mammals, melanin exists in two chemically distinct forms: the red-y ellow phaeomelanin and the brown-black eumelanin. Although administrat ion of the pigmentary hormone cu-melanocyte-stimulating hormone (alpha MSH) and its synthetic analogue Nle(4)DPhe(7) alpha MSH induces skin darkening in man, the increases in melanogenesis in cultured human mel anocytes in response to these peptides are relatively small. However, it is possible that MSH affects the eumelanin:phaeomelanin ratio rathe r than total cellular melanin. Thus, this study examined the specific effects of Nle(4)DPhe(7) alpha MSH on the two melanins in cultured hum an melanocytes, quantifying eumelanin and phaeomelanin by high perform ance liquid chromatography. Nle(4)DPhe(7) alpha MSH induced significan t increases in the eumelanin content of these cells while having lesse r and varied effects on the levels of phaeomelanin. As a consequence, the eumelanin:phaeomelanin ratio was increased in every culture. These results demonstrate that Nle(4)DPbe(7) alpha MSH affects melanin type in human melanocytes and suggest a possible mechanism bp which this p eptide induces skin darkening in man.