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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.

The Influence of Room T e m p e r a t u r e on Night-Sleep in Man Summary. After preliminary experiments had determined that the night-sleep (unclothed and uncovered) was subjectively undisturbed from 27 to 36°C, night sleep recordings were made on 10 healthy young men. 4 hrs before and after sleep, performance tests were made in constant room temperature. The subject slept at room temperatures of 27, 31 and 36°C in the climatic chamber and were studied with polygraphic sleep recordings. The following results were obtained:1. The lower room temperature, the higher the percentage of deep-sleep and RE~-sleep was. Warm nights had higher percentages of wakefulness and higher latency of REM. Subjectively at 36 ° no subject, whereas 6 of the 8 students were "refreshed" after sleeping at 27°C.2. Movements during sleep increased at higher temperatures and decreased at lower temperatures. This behaviour is useful in terms of thermoregulatiou.3. Night-sleep at 27 ° C leads to the greatest loss of body-warmth (mean: 42 cal/m'Z), especially from the core of the body and increased excretion of noradrenalin in the urine.4. The room temperature also determined the heart rate in all sleep stages. The minimal mean was found to be 52/min during the REM-stage at 27°C.5. From the follow-up observations, a carry-over effect of the room temperatures was noted in the morning. The excretions of 17-eorticosteroids and total corticoids in the urine were decreased after the 36°C nights.

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