Definition: a substance formed by the mammalian pineal gland, which appears to depress gonadal function in mammals and causes contraction of amphibian melanophores; a precursor is serotonin. Melatonin is rapidly metabolized and is taken up by all tissues. It is involved in circadian rhythms.
[melanophore + G. tonos, contraction, + -in]
Search Stedman's Medical Dictionary
Examples: glitazone, GI cocktail, etc.