Meaning of melatonin

mel•a•to•nin

Pronunciation: (mel"u-tō'nin), [key]
— n. Physiol.
  1. a hormone secreted by the pineal gland in inverse proportion to the amount of light received by the retina, important in the regulation of biorhythms: in amphibians, it causes a lightening of the skin.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.
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