MSH mainly acts on melanocytes. Melanocytes in the body are distributed in the skin and hair, the pigment layer of the iris and retina, and the pia mater. Skin melanocytes are located between the epidermis and the dermis. The melanin bodies in the cytoplasm contain tyrosinase, which can promote the conversion of tyrosine into melanin. The main function of MSH is to activate tyrosinase and promote tyrosinase synthesis, thereby promoting melanin synthesis and darkening the color of skin and hair. MSH secretion is affected by hypothalamic melanocyte-stimulating hormone releasing factor (MRF) and melanocyte-stimulating hormone release inhibitory factor (M1F).
