Adapting to phase shifts, II. Effects of melatonin and conflicting light treatment.
The effects of melatonin (MT) and placebo (P) on adaptation to a rapid 9-h advance phase shift, in the presence and absence of inappropriate bright light (BL) exposure were examined. Volunteers were initially subjected to a gradual 9-h delay phase shift over 5 days (D1-D5) using a combination of bright light and darkness/sleep. Readaptation to a subsequent rapid 9-h advance phase shift was studied using: 1) MT, 5 mg, 2300 h, D6-D8, 2) BL, 2,000 lx, 0800-1200 h, D7-D8, 3) MT+BL and 4) P, 2300 h, D6-D8. MT treatment was timed to phase advance and BL to phase delay. BL delayed the 6-sulphatoxymelatonin rhythm in five out of seven subjects. Two subjects delayed and five phase advanced with both MT and MT+BL. MT consistently improved subjective sleep, alertness, and performance even in the presence of inappropriate BL and before phase readaptation had occurred. BL improved alertness and performance transiently. The beneficial effects of MT are not wholly mediated through an effect on the biological clock.
Deacon
S
S
Chronobiology Laboratory, School of Biological Sciences, University of Surrey, Guildford, UK.
Arendt
J
J
D000223:Adaptation, Psychological / Q000187:drug effects / Q000502:physiology; D000328:Adult; D001143:Arousal / Q000187:drug effects / Q000502:physiology; D001831:Body Temperature / Q000187:drug effects / Q000502:physiology; D002940:Circadian Rhythm / Q000187:drug effects* / Q000502:physiology; D018592:Cross-Over Studies; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D008027:Light; D008297:Male; D008550:Melatonin / Q000031:analogs & derivatives / Q000494:pharmacology* / Q000652:urine; D011597:Psychomotor Performance / Q000187:drug effects / Q000502:physiology; D012890:Sleep / Q000187:drug effects / Q000502:physiology
C054513:6-sulfatoxymelatonin; D008550:Melatonin