Circulating Melatonin in Man: Episodic Secretion throughout the Light-Dark Cycle

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Abstract
A sensitive and specific RIA for melatonin has been validated for human plasma. Five young adult men had plasma samples obtained every 20 min during two 24-h periods. One was a normal active period and the other a basal period with complete bed rest. Melatonin was found to be secreted episodically throughout the 24 h in each condition, with secretory episodes clearly present during the waking day in the presence of bright light.