A comparison was made of plasma hGH and of sleep stages during one night of undistrubed sleep and one night in which sleep was interupted by an hour of enforced wakefulness folowing the end of the second NREM-REM sleep cycle in 8 normal subjects. Plasma was sampled at 15-min intervals. HGH and slow wave sleep were both significantly increased in the two cycles immediately following the period awake compared with the same two cycles during nights of uninterruped sleep. The difference arose predominantly in the fourth cycle of the night, i.e., in the second cycle after the sleep interuption. The findings are consistent with the belief that extra wakefulness brings additional sleep of high RESTORATIVE properties.

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1. The secretion of prolactin and growth-hormone (hGH) was investigated during sleep in 10 healthy volunteers (8 males and 2 females): The comparison of one baseline night, one night after daytime physical exercise, and one night with selective deprivation of sleep stages 3 and 4 and paradoxical sleep showed clear differences of prolactin and hGH secretion during sleep. 2. Prolactin secretion is entrained into the sleep cycle of Non-REM and REM periods. A maximum of plasma hormone elevations occurs during the first quarter of sleep cycles, i.e., during Non-REM periods and less frequent rises at the end of the cycles, mainly during REM periods. 3. In contrast to growth hormone, concentrations of prolactin remain high also during later cycles occurring toward morning. This shows that high prolactin, but not high concentrations of hGH, regularly occur during sleep cycles with small amounts of slow-wave sleep. 4. Maximal prolactin concentrations during sleep are affected neither by preceding daytime physical exercise nor by selective deprivation of slow sleep stages 3 and 4. This is further evidence that slow-wave sleep stages are not necessary for the development of high plasma prolactin concentrations. However, peak values of growth hormone in the first and second cycle are significantly diminished after selective deprivation of sleep stages 3 and 4. 5. In abnormally long sleep cycles with artificial delay of the first REM period, the cyclical rhythmicity of prolactin release seems disturbed. This is further evidence for the sleep-dependent rhythmicity in the secretion of this hormone.

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1. Polygraphic night sleep recordings in eight healthy male volunteers with simultaneous measurement of rectal temperature, plasma growth hormone (HGH), cortisol, and TSH concentrations were performed during normal, raised, and lowered ambient and body temperature. 2. There was a statistically significant increase in plasma cortisol and TSH levels during cold nights with a smaller rise during high temperatures. 3. Growth hormone levels, measured as the mean highest plasma concentration in the first two NREM-REM sleep cycles, were slightly lower during hot and cold nights than corresponding baseline values. It is suggested that there may be an inverse relation between ACTH and HGH secretion by the anterior pituitary gland. 4. During the nights of high ambient temperature, decreased total duration of sleep and particularly low values of paradoxical sleep were observed. Night sleep in low ambient temperature with a significant decrease of body temperature is not different from baseline conditions. 5. The results suggest that a pronounced increase in stress hormone secretion may occur without changes in polygraphic EEG criteria.