Free-running circadian rhythm of melatonin in a sighted man despite a 24-hour sleep pattern: a non-24-hour circadian syndrome.
Sleep and plasma melatonin rhythms were measured longitudinally in a sighted young man (21 years old) under a day-right environment. At each measurement, the responsiveness of the melatonin rhythm to a single light pulse was examined in addition to the 24-hour profile. In experiment 1, the timing of sleep was decided by the subject himself. Although most sleep episodes were observed between 21:02 h and 10:55 h, the plasma melatonin rhythm free-ran for a period of 24.18 h. In experiment 2, the sleep-wake schedule of the subject was strictly fixed. The subject was instructed to go do bed at 24:00 h and wake up, at the latest, before 8:00 h for 40 days. The melatonin rhythm, however, continued to free-run for a period of 24.12 h. Nocturnal melatonin level could not be suppressed by a 3-hour light pulse of 500 lx, but was suppressed by a pulse of 1000 lx. It is concluded that internal desynchronization occurred in this particular sighted subject where the sleep-wake rhythm was entrained by the 24-hour day-night environment, whereas the plasma melatonin rhythm free ran, and that a forced sleep schedule did not act as a strong zeitgeber.
Hashimoto
S
S
Department of Physiology, Hokkaido University School of Medicine, Sapporo, Japan.
Nakamura
K
K
Honma
S
S
Honma
K
K
D000328:Adult; D002940:Circadian Rhythm / Q000502:physiology*; D006801:Humans; D008027:Light; D008137:Longitudinal Studies; D008297:Male; D008550:Melatonin / Q000097:blood*; D012894:Sleep Stages / Q000502:physiology*; D012893:Sleep Wake Disorders / Q000503:physiopathology*
D008550:Melatonin