The effects of melanocyte stimulating hormone on dermal melanocytosis in Japanese monkeys

摘要

Dermal melanocytosis (DM) is a general term of benign pigmented lesions derived from dermal melanocytes (MCs). As reported in our studies, we found diffuse discolorations in the skin of Japanese monkeys. The skin appearances resulted from the optical phenomenon of dermal MCs. In this study, we investigated the effects of melanocyte stimulating hormone (MSH) on DM in the monkey. Every week for 4 weeks, the DM sites were injected subcutaneously with MSH solutions (0, 10, 100 and 1,000 μg/ml). The MSH-treated sites were weekly observed and their skin colors were also measured by the colorimeter. Tissue specimens obtained from each MSH-treated site were histopathologically examined before the study and 1 week after the completion of the MSH administration. The MSH-treated sites showed grossly moderate pigmentation. 3 colorimetric parameters (Yxy, L~*a~*b~* and L~*C~*h~* systems) of skin colors were changed in the MSH-treated sites. The luminance factors (Y and L~*) decreased 4 weeks after beginning this study. After the completion of the MSH administration, the MSH-treated sites showed morphological changes including increases in melanin granules. In the MSH-treated sites, the dermis had a large number of MCs with abundant melanin granules. The MCs had well-developed dendrites and they were distributed among the dermal reticular layer. These results revealed that the DM sites were pigmented after the MSH administration. Histopathological findings showed that dermal MCs were activated in response to administration of MSH. Our study demonstrated that dermal MCs in Japanese monkeys were not resting cells and produced actively melanin granules with morphological changes.