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Neuro-endocrine Pattern of Secretion during the Sleep–Wake Cycle of Man
Neuro-endocrine Pattern of Secretion during the Sleep-Wake Cycle of Man ELLIOT D. WEITZMAN Department of Neurology, Montefiore Hospital and Medical Center, and The Albert Einstein College of Medicine, Bronx, N . Y. 10467 (U.S.A.)
In this report I will describe two separate studies dealing with the problem of stability and environmental influence on the 24-hr pattern of the episodic secretion of cortisol in normal subjects. The first study is a comparison of the 24-hr cortisol and growth hormone (GH) secretory patterns during ambulatory functional activity and minimal activity at bed rest. This work was done in collaboration with Stephanie Erlich and Peter McGregor. Recent studies have demonstrated that the 24-hr pattern of ACTH (corticotropin)cortisol secretion consists of a sequence of temporally ordered episodic secretory patterns throughout the entire 24-hr period and that the “circadian” cycle results from the temporal clustering of episodic secretion (Weitzman et al., 1966; Hellman et at., 1970; Weitzman et al., 1971). A “basal level” or “steady state” of cortisol concentration was not found for any extended time period of the day. Only when the concentration falls to near zero, generally during the 4 hr in proximity to sleep onset, is there any prolonged period of constancy. There is considerable variability in lag time between secretory episodes and the plasma concentration at which the episodes are initiated. These findings have led us to suggest that the temporal sequence of episode initiation appears to be under CNS control as a “programmed” sequence of events, and that with a stable repetitive daily life pattern, the association of the ACTHadrenal secretory events with the sleepwaking cycle is part of a general program of biological rhythms. In these studies specific environmental factors such as conversations, reading, carrying out usual daily activities, etc. were not carefully controlled. In order to evaluate some of these factors, we recently performed a study to determine differences in the 24-hr cortisol secretory pattern between a condition of normal ambulatory “activity” and one of minimal activity, “basal”. Each of 6 normal young adult male subjects (medical students, ages 20-25) spent the waking 16 hr on two separate occasions either on a normal activity schedule of classes, meals, etc. or on strict bed rest (lights on) without reading, conversing or other external stimulation. During this latter basal condition they were fed a liquid diet given in 150 ml amounts at approximately hourly intervals. They were allowed to sleep undisturbed for as long as they pleased during this period and were polygraphically monitored during the entire “basal” day to define all daytime sleep periods. On both experimental nights Referencesp . 101-102
94
E. D. WEITZMAN
+
W
w
0 1 a - 2 m L
3
$
4 1 v) REM
E - S * 2/1/74
HCTIVITY
2453
W 0 1 W
a 1 - 2 0
L W w
i2
3 4 REM
30
c t
E.S.
3/1/74
BASAL
2456
Fig. 1 . Twenty-four-hour plasma concentration pattern of cortisol and growth hormone in one subject during the “acfivity” (A) and “basal” (B) experimental condition. Samples were obtained every 20 min from an intravenous catheter. The polygraphically defined sleep stage pattern is depicted for each sleep period. Cortisol, open circles; growth hormone, triangles.
95
SLEEP-WAKE CYCLE AND HORMONAL PATTERNS
TABLE I COMPARISON OF THE MEAN CONCENTRATION OF PLASMA CORTISOL
S.D. (pg/lOO ml) OF 8-hr CLOCK 6 SUBJECTS
TIMES FOR THE “ACTIVITY” AND “BASAL” EXPERIMENTAL CONDITIONS FOR
Clock time
Activity
Basal
Noon-8 p.m. 8 p . m . 4 a.m. 4 a.m.-noon
10.7 i 1.1
7.2 i 1.1* 4.6 2.2** 10.9 & 2.1**
4.6 rt 1.1 11.2 i 3.6
* P < 0.001 (r-test). **
N.S.
they slept in the laboratory (12 p.m.-8 a.m.) with polygraphic recording. Twentyfour-hour plasma sampling, every 20 min, was carried out with an indwelling i.v. catheter during both the “activity” and “basal” experimental 24-hr period. All subjects took naps in the “basal” condition with total sleep time during the 16 hr lights on period ranging from 131 to 408 min. In 5 of the 6 subjects, higher peak concentrations of cortisol were found during the 16-hr waking portion of the 24-hr curve on the activity than on the basal days. This difference was not present during the 8-hr sleep portion of the curve. An episodic secretory pattern was clearly present for all subjects on both the “activity” and “basal” 24-hr periods, and all subjects demonstrated the typical circadian rhythmicity for the cortisol concentrations during both periods. Statistical analysis of the mean concentrations of cortisol of the 8-hr time periods comparing “activity” with “basal” days, demonstrated that a highly significant difference was present for the clock time segment from noon to 8 p.m. (activity day, 10.7 k 1.1 pg/100 ml; basal day 7.2 k 1.1 pg/lOO ml; P < 0.001) (Table I). The other 8-hr segments (8 p . m . 4 a.m. and 4 a.m.noon) were not significantly different for the two behavioral conditions. These results indicate that a significant difference in the concentration of secreted cortisol occurs when subjects are either in a quiet, relaxed state or actively involved in usual daytime activities. In spite of this difference, the episodic ultradian and circadian patterns of hormone secretion were clearly preserved. We also measured the 24-hr pattern of GH in each of the subjects under the two different experimental conditions. All subjects secreted GH shortly after sleep onset at night as expected (Takahashi et al., 1968; Sassin et al., 1969; Pawel et al., 1972). There were 8 secretory episodes at night (midnight-8 a.m.) for the “activity” condition and 6 episodes at night for the “basal” condition. A major difference in amount and pattern of GH secretion was present during the 16-hr day. There were a total of 11 secretory episodes summed across subjects on the “activity” day, as compared with 18 on the “basal” day. Since the subjects took daytime naps which were polygraphically defined on the “basal” day, we determined the relation between the GH episodes and a sleep period. I t was found that 15 of the 18 episodes were clearly associated with a daytime deep period. An estimate of the integrated area under the GH curve for the two conditions showed an activity/basal ratio of 2-3. Therefore, more GH was secreted References p . 101-102
96
E. D. WEITZMAN
under basal “rest” conditions than when the subjects were actively engaged in normal daytime waking activities. This difference could clearly be accounted for by the presence of naps taken in the basal experimental conditions. The second study is one that concerns the seasonal pattern of sleep stages and the secretion of cortisol and growth hormone during 24-hr periods in Northern Norway. This study was done in collaboration with Drs. Andries S . deGraaf, Jon F. Sassin, Tormar Hansen, Ole B. Godtlibsen and Leon Hellrnan. Life within the Arctic Circle carries with it exposure to marked seasonal changes. Extreme shifts in the ratio of light to darkness during the course of the year is a prominent feature in these areas, ranging between the polar night and the midnight sun. There is abundant evidence that these fluctuations affect plants and animals but very little precise information about the degree to which humans are affected. Numerous complaints are heard among the general population of all age groups about disturbances in their sleep pattern, especially during the dark period o f the Arctic winter (Kleitman and Kleitman, 1953). The present experiment was designed to investigate not only seasonal variation in sleep but also alterations in the secretion of cortisol and growth hormone of 7 young men in relation to the different seasons in a subarctic region. Tromso (Norway), at about 70” N. latitude, was selected because it is the world’s northernmost neurological center with facilities for polygraphic recording. The investigations were performed during the following 4 seasonal intervals: (1) April-May, 1971; (2) July-August, 1971; (3) October-November, 1971; (4) January-February, 1972. During each period, polygraphic recordings were made on 3 consecutive nights. Over the last 24 hr, blood samples were collected every 20 min with an indwelling catheter. The subjects, 7 healthy men, members of the technical staff of the Norwegian Air Force and stationed at Bardufoss Air Force Base, about 70 miles from Tromso, participated in the study. Their ages were between 22 and 40 years. Most of them were born in northern Norway and all of them had been living there during the preceding years. Each had a private room where he could relax, listen to the radio, watch T.V. A regular hospital diet was served at 8 a.m., noon and 5 p.m. Coffee and food were not served after 8 p.m. Naps were not allowed and drugs were not used. Each subject slept in his own sound-attenuated room which was well ventilated and darkened by black curtains. Collection of blood samples was begun at 9 a.m. on the third day of each period and then sequentially sampled at 20-min intervals for the next 24 hr. The plasma was obtained and immediately frozen. Within 2 weeks after each interval, the frozen samples were packed in a container provided with freezing elements and flown to New York for the hormone determination. Although there is some variation of total sleep time among the subjects, the sleep stage percents were quite consistent across subjects for each night for stages 1, 2, and REM sleep. Stages 3 and 4 were more variable. The subjects demonstrated a decrease from approximately 20 to 15 % in REM sleep on the night of the plasma sampling as well as a small increase in waking time from approximately 5 to 12%. There was no significant difference found when sleep stage patterns of the 7 subjects
97
SLEEP-WAKE CYCLE AND HORMONAL PATTERNS
TABLE I1 SLEEP STAGE PERCENT OF TOTAL SLEEP TIME, AVERAGED FOR EACH SEASON
N
night; REM = rapid eye movement.
=
Sleep time (total) (% of total time of 8 hr) Stage 1 Stage 2 Stage 3 Stage 4 REM
Autumn
Summer
Spring
Winter
NI
N2
N3
NI
N2
N3
NI
N2
N3
NI
N2
N3
96
97
83
95
95
88
98
98
88
95
93
88
6
10 60 11 5 13
5 62 8 5 20
7 57 10 5 21
11 61 9 4 15
7 54 11 6 21
6 59 9 5 20
11 61 12 3 14
7 58 9 6 20
6 57 9 6 20
8 59 9 7 16
5 58 10 7 20
55
10 6 23
12-
CORTISOL .
Ng/tGQml
- 25
0'"1
5
CORTISOL
B-
-20
6-
- I5
4-
- 10
2-
5
-
-
Fig. 2. Bar graph of the mean and standard deviation of both the total amount of cortisol secreted (mg) and the average concentration (pg/100 ml) for 24-hr periods for all subjects as a function of yearly season. TABLE I11 MEAN PLASMA CORTISOL CONCENTRATIONS
(,ug/lOO ml)
DURING
6-hr
DAY SEGMENTS FOR THE SEASON
Clock time
Spring
Summer
Autumn
Winter
02:00-08:00 08:00-14:00 14:00-20:00
5.2 5.8 1.8
5.0 4.1 2.8
6.7 4.8 3.4 1.9
6.5 5.5 3.1 1.6
20:00-02:00
2.3
0.6
were compared as a function of yearly season. The seasonal variation in sleep stage amounts was less than that found among the individual subjects (Table 11). All subjects demonstrated the characteristic pattern of episodic secretion of cortisol for all the 24-hr periods of measurement (Hellman et al., 1970; Weitzman et al., 1971). Calculation of the 24-hr mean concentration of cortisol revealed that there was a significant difference between the winter and summer and the autumn and summer References p . 101-102
98
E. D. WEITZMAN
values (P < 0.01, < 0.02, respectively) (Fig. 2). Calculation of the mean concentration as a function of 6-hr clock segments indicated that the hours from 8 p.m. to 2 a.m. had the greatest difference between summer and the 3 other seasons (Table 111). A difference was also present during spring for the 2 p.m. to 8 p.m. clock time period. The mean 24-hr concentration and secretory amount among the individual subjects revealed no significant differences, although one subject had an unusually high mean value for both. Calculation of the mean total time spent in secretion of cortisol during the 24-hr measured periods revealed that the winter period had the highest value. However, because of the large variability across seasons and among the subjects, n o statistical difference was recognized. No significant difference in the number of secretory episodes per 24 hr was found for season or subjects. The percent deviation of each hour’s mean cortisol concentration from the 24-hr mean value was calculated and plotted as a graphic display (Fig. 3). The curves for each of the 4 seasons are remarkably similar and almost superimposable and, therefore,
1
I5Oli
A
7
-.lOOJ
-100
1
Fig. 3. The 24-hr pattern of plasma cortisol concentration expressed as percent deviation of the mean daily concentration. A, spring; B, summer; C, autumn; D, winter.
99
SLEEP-WAKE CYCLE AND HORMONAL PATTERNS
TABLE IV MEAN DURATION
(mill) OF CORTISOL INTER-EPISODE INTERVALS FOR
CLOCK TIME AND SEASONS
Clock time
Spring
Summer
Autumn
Winter
Mean
20:00-02:00 02:00-08:00 08:00-14:00 14:00-20:00
175 107 113 167
184 110 106 176
272 107 108 202
151 108 173
196 108 105 180
Mean
141
144
172
131
93
r-
560-
-
420-
2801400
rl
n r ' l____-____ L i -
4
700560
A
L
SLEEP TIME
-140'
D
560420280140-
140
I
-140l
, , , , , , , , , , , , i , , , , , , , i ,,
OK30
I400
t
111 k
_______--
1900 :ziOo 0506 L
J
SLEEP TIME
Fig. 4. The 24-hr pattern of plasma growth hormone concentration expressed as percent deviation of the mean daily concentration. A, spring; B, summer; C, autumn, D, winter.
do not demonstrate any major difference in pattern. An estimate of the length of the inter-secretory episode interval as a function of the time of the day demonstrated that the hours from 2 a.m. to 8 a.m. had a remarkably similar value across seasons whereas it was much greater and more variable between 8 p.m. and 2 a.m. (Table IV). All subjects secreted GH shortly after onset of sleep with a peak occurring approximately 2 hr after sleep onset (about 1 am.) (Takahashi et al., 1968; Sassin et al., 1969; Pawel et al., 1972). No difference in timing of release was found with regard to season of the year (Fig. 4).In addition, no difference was found regarding the sporadic References P . 101-102
100
E. D. WEITZMAN
waking daytime releases of GH as a function of season. The sleep onset related G H release was the major release of the 24 hr for all 7 subjects studied. On only 2 out of 28 occasions did a daytime G H peak concentration exceed the peak at sleep onset at night. In a study carried out in Tromso during the summer of 1951, Kleitman reported that previous anecdotal information, indicating that the residents slept very little during the all light summer months, was highly inaccurate (Kleitman and Kleitman, 1953). He found in interviews that time spent in bed during the summer months averaged 7 hr and 26 min, and 8 hr and 25 min, during winter months. Although there was considerably greater variability of the time of going to bed in the winter as compared to the summer, the time of getting up in the morning was the same for the two seasons. The data from the present study clearly support Dr. Kleitman’s survey in that essentially no difference was found for polygraphically monitored sleep between the seasons. The choice of a relatively stable group of air force personnel in our study decreased the possibility of variable life styles producing deviations of the diurnal routine of the sleep-wakefulness pattern. Therefore, it does not appear that any seasonal sleep pattern difference in man in the arctic is an obligatory direct requirement of that environment, but rather suggests that if a change does occur, the effect is an indirect one mediated through seasonally altered social and work schedules. The reproducibility and lack of difference of the 24-hr temporal pattern of cortisol and GH secretion within and across subjects is also in agreement with previous studies. All subjects had stage 3 during the first 2 hr on each of the nights of plasma sampling and had a concomitant release of GH at that time. Previous studies indicate that the stage 2-3 electroencephalographic pattern of sleep is correlated with the triggering of a G H release (Pawel et al., 1972). The clear consistent synchronization of the 24-hr cortisol and GH patterns with the stability of the sleep stage patterns and sleep-waking 24-hr rhythm is in full agreement with the concept that social and sleep cues are the dominant determinants in man of circadian phase relationships (Aschoff et al., 1971). The finding of a small but significant increase in the 24-hr mean plasma concentration and 24-hr output of cortisol during the autumn and winter months in the arctic has not been reported previously to the best of our knowledge and suggests the possibility of a circannual rhythm. The major difference in mean concentration during the afternoon and evening hours (2 p.m.-2 a.m.) suggeststhat waking behavioral activity in relation to increased environmental demands during the winter and autumn seasons may have contributed to this seasonal difference.
SUMMARY
In order to study the stability of the 24-hr pattern of the episodic secretion of cortisol and growth hormone (GH) in relation to the sleepwaking cycle of man, two studies were performed. The first is a comparison of the 24-hr cortisol and G H secretory
SLEEP-WAKE CYCLE A N D HORMONAL PATTERNS
101
pattern during ambulatory functional activity and minimal activity at bed rest. Each of 6 normal young adult male subjects (medical students, ages 20-25) spent the waking 16 hr on two separate occasions either on a normal activity schedule of classes, meals, etc. or on strict bed rest (lights on) without reading, conversing or other external stimulation. They were allowed to sleep undisturbed for as long as they pleased during this period and were polygraphically monitored during the entire “basal” day to define all daytime sleep periods. On both experimental nights they slept in the laboratory (12 p.m.-8 a.m.) with polygraphic recording. Twenty-fourhour plasma sampling, every 20 min, was carried out with an indwelling i.v. catheter during both the “activity” and “basal” experimental 24-hr period. All subjects took naps in the “basal” condition with total sleep time during the 16-hr lights on period ranging from 131 to 408 min. In 5 of the 6 subjects, higher peak concentrations of cortisol were found during the 16-hr waking portion of the 24-hr curve on the activity than on the basal days. An episodic secretory pattern was clearly present for all subjects on both the “activity” and “basal” 24-hr periods, and all subjects demonstrated the typical circadian rhythmicity for the cortisol concentrations during both periods. All subjects secreted G H shortly after sleep onset at night as expected. A major difference in amount and pattern of GH secretion was present during the 16-hr day. More GH was secreted under basal “rest” conditions than when the subjects were actively engaged in normal daytime waking activities. This difference could clearly be accounted for by the presence of naps taken in the basal experimental conditions. In a second study, a group of 7 healthy male subjects were studied in regard to sleep stages and, 24-hr plasma cortisol and GH patterns during the 4 seasons of the year in an arctic environment (Tromso, Norway). No difference in total sleep or sleep stage percents was found for any of the yearly seasons. A small but statistically significant increase in mean plasma cortisol concentration and amount secreted for 24 hr was found for the autumn-winter seasons, as compared with the spring and summer. However, no difference in the circadian curve of cortisol hormonal pattern was found. All subjects secreted G H shortly after sleep onset at night and no difference was found as a function of season of the year.
REFERENCES
J., FATRANSKA, M., GIEDKE, H., DOERR, P., STAM,D. AND WISSER,H. (1951) Human ASCHOFF, circadian rhythms in continuous darkness entrainment by social cues. Science, 171, 213-215. HELLMAN, L., NAKADA, F., CURTI,J., WEITZMAN, E. D., KREAM, J., ROFFWARG, H., ELLMAN, S., FUKUSHIMA, D. K. AND GALLAGHER, T. F. (1970) Cortisol is secreted episodically by normal man. J. din. Endocr., 30, 41 1422. KLEITMAN, N. AND KLEITMAN, H. (1953) Sleep-wakefulness pattern in arctic. Scient. Monthly, 76, 349-356. PAWEL,M. A., SASSIN,J. F. AND WEITZMAN, E. D. (1972) The temporal relation between HGH release and sleep stage changes at nocturnal sleep onset in man. Life Sci., 11, 587-593. SASSIN, J., PARKER, D. C., MACE,J. W., GOTLIN, R. W., JOHNSON, L. C. AND ROSSMAN, L. G. (1969) Human growth hormone release: relation to slow wave sleep at sleep-waking cycles. Science, 165, 513-515.
102
E. D. WEITZMAN
TAKAHASHI, Y . , KIPNIS,D. M. AND DAUGHADAY, W. H. (1968) Growth hormone secretion during sleep. J. clin. Invest., 47,2079-2090. WEITZMAN, E. D.,SCHAUMBURG, H. AND FISHBEIN, W. (1966) Plasma 17-hydroxycorticosteroid levels during sleep in man. J. din. Endocr., 26, 121-127. WEITZMAN, E. D., FUKUSHIMA, D., NOGEIRE, C., ROFFWARG, H., GALLAGHER, T. F. AND HELLMAN, L. (1971) Twenty-four hour pattern of the episodic secretion of cortisol in normal subjects. J. clin. Endocr.. 33, 14-22.
In this report I will describe two separate studies dealing with the problem of stability and environmental influence on the 24-hr pattern of the episodic secretion of cortisol in normal subjects. The first study is a comparison of the 24-hr cortisol and growth hormone (GH) secretory patterns during ambulatory functional activity and minimal activity at bed rest. This work was done in collaboration with Stephanie Erlich and Peter McGregor. Recent studies have demonstrated that the 24-hr pattern of ACTH (corticotropin)cortisol secretion consists of a sequence of temporally ordered episodic secretory patterns throughout the entire 24-hr period and that the “circadian” cycle results from the temporal clustering of episodic secretion (Weitzman et al., 1966; Hellman et at., 1970; Weitzman et al., 1971). A “basal level” or “steady state” of cortisol concentration was not found for any extended time period of the day. Only when the concentration falls to near zero, generally during the 4 hr in proximity to sleep onset, is there any prolonged period of constancy. There is considerable variability in lag time between secretory episodes and the plasma concentration at which the episodes are initiated. These findings have led us to suggest that the temporal sequence of episode initiation appears to be under CNS control as a “programmed” sequence of events, and that with a stable repetitive daily life pattern, the association of the ACTHadrenal secretory events with the sleepwaking cycle is part of a general program of biological rhythms. In these studies specific environmental factors such as conversations, reading, carrying out usual daily activities, etc. were not carefully controlled. In order to evaluate some of these factors, we recently performed a study to determine differences in the 24-hr cortisol secretory pattern between a condition of normal ambulatory “activity” and one of minimal activity, “basal”. Each of 6 normal young adult male subjects (medical students, ages 20-25) spent the waking 16 hr on two separate occasions either on a normal activity schedule of classes, meals, etc. or on strict bed rest (lights on) without reading, conversing or other external stimulation. During this latter basal condition they were fed a liquid diet given in 150 ml amounts at approximately hourly intervals. They were allowed to sleep undisturbed for as long as they pleased during this period and were polygraphically monitored during the entire “basal” day to define all daytime sleep periods. On both experimental nights Referencesp . 101-102
94
E. D. WEITZMAN
+
W
w
0 1 a - 2 m L
3
$
4 1 v) REM
E - S * 2/1/74
HCTIVITY
2453
W 0 1 W
a 1 - 2 0
L W w
i2
3 4 REM
30
c t
E.S.
3/1/74
BASAL
2456
Fig. 1 . Twenty-four-hour plasma concentration pattern of cortisol and growth hormone in one subject during the “acfivity” (A) and “basal” (B) experimental condition. Samples were obtained every 20 min from an intravenous catheter. The polygraphically defined sleep stage pattern is depicted for each sleep period. Cortisol, open circles; growth hormone, triangles.
95
SLEEP-WAKE CYCLE AND HORMONAL PATTERNS
TABLE I COMPARISON OF THE MEAN CONCENTRATION OF PLASMA CORTISOL
S.D. (pg/lOO ml) OF 8-hr CLOCK 6 SUBJECTS
TIMES FOR THE “ACTIVITY” AND “BASAL” EXPERIMENTAL CONDITIONS FOR
Clock time
Activity
Basal
Noon-8 p.m. 8 p . m . 4 a.m. 4 a.m.-noon
10.7 i 1.1
7.2 i 1.1* 4.6 2.2** 10.9 & 2.1**
4.6 rt 1.1 11.2 i 3.6
* P < 0.001 (r-test). **
N.S.
they slept in the laboratory (12 p.m.-8 a.m.) with polygraphic recording. Twentyfour-hour plasma sampling, every 20 min, was carried out with an indwelling i.v. catheter during both the “activity” and “basal” experimental 24-hr period. All subjects took naps in the “basal” condition with total sleep time during the 16 hr lights on period ranging from 131 to 408 min. In 5 of the 6 subjects, higher peak concentrations of cortisol were found during the 16-hr waking portion of the 24-hr curve on the activity than on the basal days. This difference was not present during the 8-hr sleep portion of the curve. An episodic secretory pattern was clearly present for all subjects on both the “activity” and “basal” 24-hr periods, and all subjects demonstrated the typical circadian rhythmicity for the cortisol concentrations during both periods. Statistical analysis of the mean concentrations of cortisol of the 8-hr time periods comparing “activity” with “basal” days, demonstrated that a highly significant difference was present for the clock time segment from noon to 8 p.m. (activity day, 10.7 k 1.1 pg/100 ml; basal day 7.2 k 1.1 pg/lOO ml; P < 0.001) (Table I). The other 8-hr segments (8 p . m . 4 a.m. and 4 a.m.noon) were not significantly different for the two behavioral conditions. These results indicate that a significant difference in the concentration of secreted cortisol occurs when subjects are either in a quiet, relaxed state or actively involved in usual daytime activities. In spite of this difference, the episodic ultradian and circadian patterns of hormone secretion were clearly preserved. We also measured the 24-hr pattern of GH in each of the subjects under the two different experimental conditions. All subjects secreted GH shortly after sleep onset at night as expected (Takahashi et al., 1968; Sassin et al., 1969; Pawel et al., 1972). There were 8 secretory episodes at night (midnight-8 a.m.) for the “activity” condition and 6 episodes at night for the “basal” condition. A major difference in amount and pattern of GH secretion was present during the 16-hr day. There were a total of 11 secretory episodes summed across subjects on the “activity” day, as compared with 18 on the “basal” day. Since the subjects took daytime naps which were polygraphically defined on the “basal” day, we determined the relation between the GH episodes and a sleep period. I t was found that 15 of the 18 episodes were clearly associated with a daytime deep period. An estimate of the integrated area under the GH curve for the two conditions showed an activity/basal ratio of 2-3. Therefore, more GH was secreted References p . 101-102
96
E. D. WEITZMAN
under basal “rest” conditions than when the subjects were actively engaged in normal daytime waking activities. This difference could clearly be accounted for by the presence of naps taken in the basal experimental conditions. The second study is one that concerns the seasonal pattern of sleep stages and the secretion of cortisol and growth hormone during 24-hr periods in Northern Norway. This study was done in collaboration with Drs. Andries S . deGraaf, Jon F. Sassin, Tormar Hansen, Ole B. Godtlibsen and Leon Hellrnan. Life within the Arctic Circle carries with it exposure to marked seasonal changes. Extreme shifts in the ratio of light to darkness during the course of the year is a prominent feature in these areas, ranging between the polar night and the midnight sun. There is abundant evidence that these fluctuations affect plants and animals but very little precise information about the degree to which humans are affected. Numerous complaints are heard among the general population of all age groups about disturbances in their sleep pattern, especially during the dark period o f the Arctic winter (Kleitman and Kleitman, 1953). The present experiment was designed to investigate not only seasonal variation in sleep but also alterations in the secretion of cortisol and growth hormone of 7 young men in relation to the different seasons in a subarctic region. Tromso (Norway), at about 70” N. latitude, was selected because it is the world’s northernmost neurological center with facilities for polygraphic recording. The investigations were performed during the following 4 seasonal intervals: (1) April-May, 1971; (2) July-August, 1971; (3) October-November, 1971; (4) January-February, 1972. During each period, polygraphic recordings were made on 3 consecutive nights. Over the last 24 hr, blood samples were collected every 20 min with an indwelling catheter. The subjects, 7 healthy men, members of the technical staff of the Norwegian Air Force and stationed at Bardufoss Air Force Base, about 70 miles from Tromso, participated in the study. Their ages were between 22 and 40 years. Most of them were born in northern Norway and all of them had been living there during the preceding years. Each had a private room where he could relax, listen to the radio, watch T.V. A regular hospital diet was served at 8 a.m., noon and 5 p.m. Coffee and food were not served after 8 p.m. Naps were not allowed and drugs were not used. Each subject slept in his own sound-attenuated room which was well ventilated and darkened by black curtains. Collection of blood samples was begun at 9 a.m. on the third day of each period and then sequentially sampled at 20-min intervals for the next 24 hr. The plasma was obtained and immediately frozen. Within 2 weeks after each interval, the frozen samples were packed in a container provided with freezing elements and flown to New York for the hormone determination. Although there is some variation of total sleep time among the subjects, the sleep stage percents were quite consistent across subjects for each night for stages 1, 2, and REM sleep. Stages 3 and 4 were more variable. The subjects demonstrated a decrease from approximately 20 to 15 % in REM sleep on the night of the plasma sampling as well as a small increase in waking time from approximately 5 to 12%. There was no significant difference found when sleep stage patterns of the 7 subjects
97
SLEEP-WAKE CYCLE AND HORMONAL PATTERNS
TABLE I1 SLEEP STAGE PERCENT OF TOTAL SLEEP TIME, AVERAGED FOR EACH SEASON
N
night; REM = rapid eye movement.
=
Sleep time (total) (% of total time of 8 hr) Stage 1 Stage 2 Stage 3 Stage 4 REM
Autumn
Summer
Spring
Winter
NI
N2
N3
NI
N2
N3
NI
N2
N3
NI
N2
N3
96
97
83
95
95
88
98
98
88
95
93
88
6
10 60 11 5 13
5 62 8 5 20
7 57 10 5 21
11 61 9 4 15
7 54 11 6 21
6 59 9 5 20
11 61 12 3 14
7 58 9 6 20
6 57 9 6 20
8 59 9 7 16
5 58 10 7 20
55
10 6 23
12-
CORTISOL .
Ng/tGQml
- 25
0'"1
5
CORTISOL
B-
-20
6-
- I5
4-
- 10
2-
5
-
-
Fig. 2. Bar graph of the mean and standard deviation of both the total amount of cortisol secreted (mg) and the average concentration (pg/100 ml) for 24-hr periods for all subjects as a function of yearly season. TABLE I11 MEAN PLASMA CORTISOL CONCENTRATIONS
(,ug/lOO ml)
DURING
6-hr
DAY SEGMENTS FOR THE SEASON
Clock time
Spring
Summer
Autumn
Winter
02:00-08:00 08:00-14:00 14:00-20:00
5.2 5.8 1.8
5.0 4.1 2.8
6.7 4.8 3.4 1.9
6.5 5.5 3.1 1.6
20:00-02:00
2.3
0.6
were compared as a function of yearly season. The seasonal variation in sleep stage amounts was less than that found among the individual subjects (Table 11). All subjects demonstrated the characteristic pattern of episodic secretion of cortisol for all the 24-hr periods of measurement (Hellman et al., 1970; Weitzman et al., 1971). Calculation of the 24-hr mean concentration of cortisol revealed that there was a significant difference between the winter and summer and the autumn and summer References p . 101-102
98
E. D. WEITZMAN
values (P < 0.01, < 0.02, respectively) (Fig. 2). Calculation of the mean concentration as a function of 6-hr clock segments indicated that the hours from 8 p.m. to 2 a.m. had the greatest difference between summer and the 3 other seasons (Table 111). A difference was also present during spring for the 2 p.m. to 8 p.m. clock time period. The mean 24-hr concentration and secretory amount among the individual subjects revealed no significant differences, although one subject had an unusually high mean value for both. Calculation of the mean total time spent in secretion of cortisol during the 24-hr measured periods revealed that the winter period had the highest value. However, because of the large variability across seasons and among the subjects, n o statistical difference was recognized. No significant difference in the number of secretory episodes per 24 hr was found for season or subjects. The percent deviation of each hour’s mean cortisol concentration from the 24-hr mean value was calculated and plotted as a graphic display (Fig. 3). The curves for each of the 4 seasons are remarkably similar and almost superimposable and, therefore,
1
I5Oli
A
7
-.lOOJ
-100
1
Fig. 3. The 24-hr pattern of plasma cortisol concentration expressed as percent deviation of the mean daily concentration. A, spring; B, summer; C, autumn; D, winter.
99
SLEEP-WAKE CYCLE AND HORMONAL PATTERNS
TABLE IV MEAN DURATION
(mill) OF CORTISOL INTER-EPISODE INTERVALS FOR
CLOCK TIME AND SEASONS
Clock time
Spring
Summer
Autumn
Winter
Mean
20:00-02:00 02:00-08:00 08:00-14:00 14:00-20:00
175 107 113 167
184 110 106 176
272 107 108 202
151 108 173
196 108 105 180
Mean
141
144
172
131
93
r-
560-
-
420-
2801400
rl
n r ' l____-____ L i -
4
700560
A
L
SLEEP TIME
-140'
D
560420280140-
140
I
-140l
, , , , , , , , , , , , i , , , , , , , i ,,
OK30
I400
t
111 k
_______--
1900 :ziOo 0506 L
J
SLEEP TIME
Fig. 4. The 24-hr pattern of plasma growth hormone concentration expressed as percent deviation of the mean daily concentration. A, spring; B, summer; C, autumn, D, winter.
do not demonstrate any major difference in pattern. An estimate of the length of the inter-secretory episode interval as a function of the time of the day demonstrated that the hours from 2 a.m. to 8 a.m. had a remarkably similar value across seasons whereas it was much greater and more variable between 8 p.m. and 2 a.m. (Table IV). All subjects secreted GH shortly after onset of sleep with a peak occurring approximately 2 hr after sleep onset (about 1 am.) (Takahashi et al., 1968; Sassin et al., 1969; Pawel et al., 1972). No difference in timing of release was found with regard to season of the year (Fig. 4).In addition, no difference was found regarding the sporadic References P . 101-102
100
E. D. WEITZMAN
waking daytime releases of GH as a function of season. The sleep onset related G H release was the major release of the 24 hr for all 7 subjects studied. On only 2 out of 28 occasions did a daytime G H peak concentration exceed the peak at sleep onset at night. In a study carried out in Tromso during the summer of 1951, Kleitman reported that previous anecdotal information, indicating that the residents slept very little during the all light summer months, was highly inaccurate (Kleitman and Kleitman, 1953). He found in interviews that time spent in bed during the summer months averaged 7 hr and 26 min, and 8 hr and 25 min, during winter months. Although there was considerably greater variability of the time of going to bed in the winter as compared to the summer, the time of getting up in the morning was the same for the two seasons. The data from the present study clearly support Dr. Kleitman’s survey in that essentially no difference was found for polygraphically monitored sleep between the seasons. The choice of a relatively stable group of air force personnel in our study decreased the possibility of variable life styles producing deviations of the diurnal routine of the sleep-wakefulness pattern. Therefore, it does not appear that any seasonal sleep pattern difference in man in the arctic is an obligatory direct requirement of that environment, but rather suggests that if a change does occur, the effect is an indirect one mediated through seasonally altered social and work schedules. The reproducibility and lack of difference of the 24-hr temporal pattern of cortisol and GH secretion within and across subjects is also in agreement with previous studies. All subjects had stage 3 during the first 2 hr on each of the nights of plasma sampling and had a concomitant release of GH at that time. Previous studies indicate that the stage 2-3 electroencephalographic pattern of sleep is correlated with the triggering of a G H release (Pawel et al., 1972). The clear consistent synchronization of the 24-hr cortisol and GH patterns with the stability of the sleep stage patterns and sleep-waking 24-hr rhythm is in full agreement with the concept that social and sleep cues are the dominant determinants in man of circadian phase relationships (Aschoff et al., 1971). The finding of a small but significant increase in the 24-hr mean plasma concentration and 24-hr output of cortisol during the autumn and winter months in the arctic has not been reported previously to the best of our knowledge and suggests the possibility of a circannual rhythm. The major difference in mean concentration during the afternoon and evening hours (2 p.m.-2 a.m.) suggeststhat waking behavioral activity in relation to increased environmental demands during the winter and autumn seasons may have contributed to this seasonal difference.
SUMMARY
In order to study the stability of the 24-hr pattern of the episodic secretion of cortisol and growth hormone (GH) in relation to the sleepwaking cycle of man, two studies were performed. The first is a comparison of the 24-hr cortisol and G H secretory
SLEEP-WAKE CYCLE A N D HORMONAL PATTERNS
101
pattern during ambulatory functional activity and minimal activity at bed rest. Each of 6 normal young adult male subjects (medical students, ages 20-25) spent the waking 16 hr on two separate occasions either on a normal activity schedule of classes, meals, etc. or on strict bed rest (lights on) without reading, conversing or other external stimulation. They were allowed to sleep undisturbed for as long as they pleased during this period and were polygraphically monitored during the entire “basal” day to define all daytime sleep periods. On both experimental nights they slept in the laboratory (12 p.m.-8 a.m.) with polygraphic recording. Twenty-fourhour plasma sampling, every 20 min, was carried out with an indwelling i.v. catheter during both the “activity” and “basal” experimental 24-hr period. All subjects took naps in the “basal” condition with total sleep time during the 16-hr lights on period ranging from 131 to 408 min. In 5 of the 6 subjects, higher peak concentrations of cortisol were found during the 16-hr waking portion of the 24-hr curve on the activity than on the basal days. An episodic secretory pattern was clearly present for all subjects on both the “activity” and “basal” 24-hr periods, and all subjects demonstrated the typical circadian rhythmicity for the cortisol concentrations during both periods. All subjects secreted G H shortly after sleep onset at night as expected. A major difference in amount and pattern of GH secretion was present during the 16-hr day. More GH was secreted under basal “rest” conditions than when the subjects were actively engaged in normal daytime waking activities. This difference could clearly be accounted for by the presence of naps taken in the basal experimental conditions. In a second study, a group of 7 healthy male subjects were studied in regard to sleep stages and, 24-hr plasma cortisol and GH patterns during the 4 seasons of the year in an arctic environment (Tromso, Norway). No difference in total sleep or sleep stage percents was found for any of the yearly seasons. A small but statistically significant increase in mean plasma cortisol concentration and amount secreted for 24 hr was found for the autumn-winter seasons, as compared with the spring and summer. However, no difference in the circadian curve of cortisol hormonal pattern was found. All subjects secreted G H shortly after sleep onset at night and no difference was found as a function of season of the year.
REFERENCES
J., FATRANSKA, M., GIEDKE, H., DOERR, P., STAM,D. AND WISSER,H. (1951) Human ASCHOFF, circadian rhythms in continuous darkness entrainment by social cues. Science, 171, 213-215. HELLMAN, L., NAKADA, F., CURTI,J., WEITZMAN, E. D., KREAM, J., ROFFWARG, H., ELLMAN, S., FUKUSHIMA, D. K. AND GALLAGHER, T. F. (1970) Cortisol is secreted episodically by normal man. J. din. Endocr., 30, 41 1422. KLEITMAN, N. AND KLEITMAN, H. (1953) Sleep-wakefulness pattern in arctic. Scient. Monthly, 76, 349-356. PAWEL,M. A., SASSIN,J. F. AND WEITZMAN, E. D. (1972) The temporal relation between HGH release and sleep stage changes at nocturnal sleep onset in man. Life Sci., 11, 587-593. SASSIN, J., PARKER, D. C., MACE,J. W., GOTLIN, R. W., JOHNSON, L. C. AND ROSSMAN, L. G. (1969) Human growth hormone release: relation to slow wave sleep at sleep-waking cycles. Science, 165, 513-515.
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TAKAHASHI, Y . , KIPNIS,D. M. AND DAUGHADAY, W. H. (1968) Growth hormone secretion during sleep. J. clin. Invest., 47,2079-2090. WEITZMAN, E. D.,SCHAUMBURG, H. AND FISHBEIN, W. (1966) Plasma 17-hydroxycorticosteroid levels during sleep in man. J. din. Endocr., 26, 121-127. WEITZMAN, E. D., FUKUSHIMA, D., NOGEIRE, C., ROFFWARG, H., GALLAGHER, T. F. AND HELLMAN, L. (1971) Twenty-four hour pattern of the episodic secretion of cortisol in normal subjects. J. clin. Endocr.. 33, 14-22.