melanotropinmedical dictionary

A polypeptide hormone secreted by the intermediate lobe of the hypophysis in humans (in neurohypophysis in certain other species) which causes dispersion of melanin by melanophores, resulting in darkening of the skin, presumably by promoting melanin synthesis; this effect is readily demonstated in some lower vertebrates, such as frogs and fish; alpha-melanotropin is an N-acetylated peptide with 13 amino acids; beta-melanotropin has 22 amino acids.

Synonyms: intermedin, melanocyte-stimulating hormone, melanophore-expanding principle.

(05 Mar 2000)