Circadian and seasonal changes in human plasma orexin-A and serum melatonin

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1. Sleep onset, offset and serum melatoninSubjects were eight healthy young adults (mean age 24.8 years) who lived around Kofu, Japan, Written informed consent was obtained from all the subjects. Kofu is located at 35°40' N and 138°34'E, and sunrise and sunset times in the summer and winter differ by about 2 h and 20 min. In Japan daylight-saving time has not been introduced. The subjects filled out a sleep log for one month in both the summer and winter, and the sleep-wake state was scored in 10-minute epochs. Based on the sleep log, daily sleep onset and offset times were looked for, and individual monthly averages were calculated. The subjects stayed in the experimental facility for 24 h in both the summer and winter. Illumination in the facility was less than 15 1x. Blood was sampled through an indwelling catheter in the forearm vein at 1-h to 3-h intervals. Serum melatonin was assayed by RIA. The phase of maximum of fitted three-harmonic regression model (3HMAX) was calculated. Sleep onset times were 0141 h in the summer and 0200 h in the winter (statistically n. s.), and sleep offset times were 0751 h and 0824 h, respectively. 3HMAX were 0258 h in the summer and 0406 h in the winter.2. Orexin-AWritten informed consent was obtained from all the subjects. Five subjects (26.0 years) stayed in the experimental facility for 24 h in both the summer and winter. Blood was sampled at 1-h intervals. Plasma orexin-A was assayed by RIA. Plasma orexin-A showed no circadian variation in both the summer and winter. But orexin-A in the summer (mean value 47.1 pg/ml) was higher than that in the winter (21.4 pg/ml).