Light exposure reduces and pinealectomy virtually stops urinary excretion of 6-hydroxymelatonin by rhesus monkeys.
The major metabolite of the pineal hormone melatonin, conjugated 6-hydroxymelatonin, was hydrolyzed, separated from the urine of rhesus monkeys, and assayed mass spectrometrically. The daily excretion pattern reflected pineal melatonin synthetic activity, being 5- to 16-fold higher at night than during the day. Progressive lengthening of the daily photoperiod beyond 12 h decreased the daily excretion of 6-hydroxymelatonin proportional to the increase duration of light exposure. Constant light reduced daily excretion by 90%, and pinealectomy reduced daily excretion by 96%. These results demonstrate the absence of significant extrapineal contributions to the urinary melatonin metabolite and confirm the use of 6-hydroxymelatonin excretion rates as a valid index of pineal gland melatonin synthesis.
D000818:Animals; D002940:Circadian Rhythm; D003624:Darkness; D008027:Light; D008253:Macaca mulatta; D008297:Male; D008550:Melatonin / Q000031:analogs & derivatives* / Q000652:urine; D010870:Pineal Gland / Q000502:physiology*
D008550:Melatonin; C012365:6-hydroxymelatonin