PIGMENT CELL REGULATORY FACTORS

[摘要] Melanin is formed enzymically by the reaction of tyrosinase with oxygen and tyrosine. Altered enzymic activity accounts for some clinical changes in pigmentation such as those occurring in albinism, phenylpyruvic oligophrenia, heavy metal toxicity and with topical application of monobenzyl ether of hydroquinone. The melanocyte stimulating hormones from the pituitary gland darken the pigment cells of man and lower animals and probably are responsible for the hyperpigmentation seen in Addison''s disease and in patients with some pituitary tumors. Melantonin, recently isolated from the pineal gland of cows and also present in peripheral nerves, lightens the pigment cells of frogs and decreases the melanin content of frog skin and hamster melanomas. Its effects in human pigmentation is not known. When melanocytes of marine animals are treated with darkening agents, melanin granules become dispersed, making the pigment cells appear dark and opaque. When lightening agents are used, melanin granules clump together towards the center of the melanocyte so that most of the cell appears light and transparent. An hypothesis is suggested to correlate hormonal and enzymic activities in pigmentation control.