title: Studies of the 24 hour rhythm of melatonin in man.
abstract: In a series of four separate studies of the 24-hour pattern of melatonin secretory function in man, the following results were obtained. Sequential measurement of the concentration of melatonin in plasma and urine demonstrated a 24-hour rhythm in which more melatonin is secreted during the sleep-lights off as compared to the waking-lights on period. However, during "free-running" and after an acute phase shift of the sleep-wake cycle, a melatonin rhythm can be dissociated from the sleep-lights out rhythm. A radioimmunoassayable plasma melatonin substance was found in significant amounts throughout the entire 24-hour day using a frequent sampling technique (every 20 min). Melatonin appears to be secreted into the blood in discrete brief episodes superimposed on a maintained "baseline" concentration. The half-life appears to be less than 30 min.
mesh_terms: D000328:Adult; D002940:Circadian Rhythm; D003624:Darkness; D006207:Half-Life; D006801:Humans; D008027:Light; D008297:Male; D008550:Melatonin / Q000378:metabolism*; D008875:Middle Aged; D012890:Sleep
chemical_list: D008550:Melatonin