Effects of a Prolonged 3-Hour Sleep-Wake Cycle on Sleep Stages, Plasma Cortisol, Growth Hormone and Body Temperature in Man*

After 1 week of a normal control (baseline) period, 7 healthy young adult subjects were subjected to a 3-hr sleep-wake schedule, (ultradian) which was adhered to for 10 days. They were allowed eight 1 hr sleep times, equally spaced throughout each 24 hr period. They were then allowed a normal nocturnal 8-hr sleep time for 7 days. During all lights-out sleep periods, poly-graphic definition of sleep stages and waking time was made. On the sixth 24-hr period of the first week (baseline) and on the eighth 24-hr period of the ultradian period, sequential 20-min plasma samples were obtained by means of an indwelling intravenous catheter. Rectal temperature was obtained at regularly spaced frequent intervals. Despite significant sleep deprivation, a circadian pattern of total sleep time persisted throughout the 10-day ultradian condition. The distribution and amount of REM sleep time was most affected with stages 3–4 sleep least affected. The time of maximum sleep was delayed by approximately 6 hr. The temporal pattern of the secretory episodes of cortisol and the body temperature curves demonstrated a persistence of the 24-hr (circadian) periodicity for all subjects during the ultradian condition. A 3-hr cortisol cycle was superimposed on the 24-hr pattern. This 3-hr cycle was entrained to the 3-hr sleep-waking cycle such that low plasma concentrations of cortisol were associated with the dark (sleep) period and high concentrations with the first hour after “lights on.” No correlation could be demonstrated between a specific sleep stage and the subsequent release of hormone even though a correlation was present for total sleep. The mean 24-hr output of GH was not different for the baseline and ultradian conditions. However, the sharp peak of GH secretion found between 11 PM to 1 AM in the baseline condition was not present in the ultradian condition. The persistence of a 24-hr temperature curve, sleep-waking cycle and cortisol pattern in spite of the attempt to disrupt these functions for 10 days demonstrates the highly resistant nature of these systems.