melanocyte-stimulating hormone MSH) A hormone, secreted in the anterior region of the pituitary gland, that stimulates the concentration of melanin granules in the chromatophores of the skin of lower vertebrates, such as amphibians. The role of MSH in humans and other mammals is not clearly understood.

melanocyte-stimulating hormone (MSH) n. a hormone synthesized and released by the pituitary gland. In amphibians MSH brings about colour changes in the skin but its physiological role in humans is uncertain.