Melatonin Synthesis in thePineal Gland: Control by Light

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Science  22 Nov 1963:
Vol. 142, Issue 3595, pp. 1071-1073
DOI: 10.1126/science.142.3595.1071


In rats placed in continuous darkness for 6 days, there is a striking increase in the activity of melatonin-synthesizing-enzyme (hydroxyindole-0-methyl transferase) in the pineal gland, but no change in the activity of monoamine oxidase. Since melatonin appears to have a hormonal role in mammals, and its synthesis is confined to the pineal gland, the inhibition of hydroxyindole-O-methyl transferase by light may constitute a mechanism of neuroendocrine regulation.