Stimulation of melanogenesis by cholecalciferol in cultured human melanocytes: a possible mechanism underlying pigmentation after ultraviolet irradiation.

An increase in the amount of tyrosinase was demonstrated in the cultured human melanocyte after 6-day culturing with cholecalciferol (vitamin D3) by increased intensity of the immunofluorescent staining using monoclonal antibody against tyrosinase. Furthermore, the melanocytes became more dendritic as noted in those in the skin after the irradiation of ultraviolet. However, 7-dehydrocholesterol (pro-vitamin D3) or 1 alpha, 25-dihydroxy-vitamin D3 (activated vitamin D3) did not induce any such effect on the cultured human melanocytes. Since cholecalciferol is known to be photo-chemically converted by the ultraviolet irradiation from pro-vitamin D3 produced in the skin, the so-far-unknown mechanism of human skin pigmentation after the ultraviolet irradiation may be partly explained by this stimulating effect of vitamin D3 on the melanocytes.