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Effects of growth hormone on sleep-waking patterns in cats
HORMONES
AND BEHAVIOR,
Effects
WARREN
6, 189-196 (1975)
of Growth Hormone on Sleep-Waking Patterns in Cats’
C. STERN,
JOHN E. JALOWIEC, HARLAN and PETER J. MORGANE
SHABSHELOWITZ,
Worcester Foundation for Experimental Biology, Shrewsbury, Massachusetts 01.545
Cats given growth hormone in doses from 50-1000 pg, i.p., showed a selective elevation of REM sleep in the fist 3 hr postinjection. Bovine thyrotropin control injections did not alter sleep patterns. When the effect of growth hormone on sleep was blocked by REM deprivation for the first 3 hr, the REM elevating effect of growth hormone still occurred in the subsequent sleep period. These results suggest that growth hormone affects the central nervous system, either directly or indirectly. Also, the greatly increased secretion of growth hormone, which has been reported during slow-wave sleep in man, may play a role in the occurrence of REM sleep.
INTRODUCTION One fundamental characteristic of normal mammalian adult sleep cycles is that slow-wave sleep (SWS) always precedes the occurrence of rapid eye movement (REM) sleep. Since several investigators have reported that in man plasma growth hormone (GH) levels are markedly elevated during the period of the night occupied by SWS (Takahashi, Kipnis and Daughaday, 1968; Honda, Takahashi, Takahashi, Azumi, Sakuma, Tsushima and Shimtiu, 1969; Sassin, Parker, Mace, Gotlin, Johnson and Rossman, 1969) the possibility arises that GH secretion during SWS may play a role in the subsequent occurrence of REM sleep. We investigated this potential relationship by administering bovine GH to cats and recording the subsequent sleep-waking patterns. Bovine GH is biologically active in cats as shown by stimulation of there has been no examination of growth (Geschwind, 1967). However, whether pituitary GH is released during SWS in the cat as occurs in man.
IThis research was supported by grants MH 02211, MH 10625, HD 06364 and by funds from the Worcester Foundation for Experimental Biology.
189 Copyright @ 1975 by Academic Press, Inc. All rights of reproduction in any form reserved.
190
STERN ET AL.
EXPERIMENT 1 Method
Seven adult female cats (Fauna Laboratories, Hudson, MA) were inplanted with electrodes for recording EEG activity of the cortex (frontal and occipital poles), hippocampus, lateral geniculate nucleus (LGN), and neck EMG and eye movements. They were housed on a 12: 12 1ight:dark cycle (0700-1900 hr lights on) with ad lib. accessto food and water. Starting at least one week after surgery each cat received three to five 7 hr baseline polygraphic recording sessions using the apparatus, recording and scoring (waking, SWS, REM sleep) procedures described by Stern and Morgane (1973). Briefly, the cats were placed in an electrically shielded, sound attenuated room and connected to Grass instrument polygraphs using a counter-weighted slip-ring cable system which allowed free movement. With respect to EEG scoring, waking was characterized by a low voltage cortical EEG, high neck muscle tonus and occasional bursts of eye movements and hippocampal theta rhythm (4-7 cycles/set). SWS was identified by a high voltage, low frequency cortical and hippocampal EEG, no eye movementsand low muscle tonus. REM sleep consisted of an activated cortical EEG, continual hippocampal theta rhythm, bursts of eye movements,neck muscle atonia and monophasic spiking in the EEG of the LGN channel. Then, at the start of either a saline (0.9%) vehicle, bovine thyrotropin or bovine GH (both hormones obtained from Calbiochem, San Diego, CA). Thyrotropin and GH were dissolved in saline. The GH doses given in random order to each cat were: 1000, 500, 100, 50, and 0.5 or 0.051.rg-two cats also received a 3OOOpg dose (each dose given once per cat). The saline injections were randomly interspersedbetween the GH sessions.Both bovine growth hormone and thyrotropin are polypeptide hormones of similar molecular weight, about 21,000. The thyrotropin control injections were given after the GH injection seriesand were 100 and SOOpg. RESULTS Table 1 shows the effects of bovine GH injection on sleep-waking percentages.The results are divided into two time periods-the first 3 hr postinjection and the subsequent4 hr. This was done since the REM ebvating effects of GH occurred for about 3 hr. Baselinevalues represent the meansof 3-5 sevenhr recording sessionsfor each cat. Statistical comparisonsof baseline vs. postinjection scores were made using analyses of variance with repeated measuresfor each of the rows in Table 1 and the studentized range statistic for the post hoc tests (Winer, 1962). The standard errors in Table 1 are based on between subject data, whereas the statistical analysis was within subjects.
*p< .05, 2-tailed.
1000 /.Jg
0.05-0.5 pg 50% 100 Pg 5OO!Jg
Growth hormone
500/G
Baseline Saline Thyrotropin 50/G
4 7 7 7 7
48,0?5 29.6*7 36.4t8 34.3+8 33.0?8
38.2*8 38.9*8
6 5
7
42.028 39.9+ 10
Wake
7
n
43.1?4 51.5*4 46.0?6 49.1+5 50.1*5
51.6+5 49.1+6
46.6+5 46.3~7
SWS
hr l-3
9.lt8 18.6*8* 17.6?8* 17.1*8* 16.4+7*
10.2+5 12.0t4
11.3*5 13.9a6
REM
61.2+5* 62.7*7* 59.6t5 65.4?6* 59.0+7
66.1+12 60.8*14
45.357 61.0+8*
Wake
Mean f SE percent of recording time
26.4+1* 28.3t4 30.1+4 24.4?5* 30.156
21.6+9 31.8211
39.1+4 28.4*6
sws
hr 4-l
Effects of Bovine Growth Hormone and Thyrotropin on Sleep-Waking Percentages in Cats.
TABLE 1
12.2*2 9.052 10.7+2 10.1-?2 10.6+2
6.4+3 8.4+3
15.3*3 10.4t3
REM
5 3
$
2 Ei
u $
%
8
F
192
STERN ET AL.
The results show that in the first 3 hr following GH injection REM time was significantly elevated by 50% above baseline at the 50, 100, 500 and 1000 @gdoses.Dosesabove or below this range did not increaseREM sleep (2 cats received a dose of 3000 pg of GH and showed mainly waking behavior for the next 7 hr). Interestingly, the REM elevating effects of the 50-1000 pg dosesof GH were essentially the same.The maximum increasein the amount of REM sleep in the first 3 hr occurred in the 50 pg group, with an elevation from 11.3% of recording time during baselineto 18.6%after GH. In comparison to the saline injected group, which showed a nonsignificant rise in REM time, the 50-104lOMggroups (pooled) showed a significant increase beyond the saline effect of 3.6% of recording time Cp< .Ol, 2-tailed test). The thyrotropin controls showed no appreciable change in the percentages or latencies of REM, SWSor waking. An example of the effects of GH on REM latencies, REM length and number of REM periodslhr within the first 3 hr post-GH is found in the results of the 50 pg group. This group showed a latency to the first REM period of 47 f 8 min (mean + SE) compared to baseline latencies of 74 + 11 min 0, < .Ol, 2-tailed t-test). SWSlatencies did not change significantly (post-GH latency of 25 + 9 min, baseline latency of 34 ?I 10 min). After 50 pg of GH the REM periods/hr and length of the averageREM episode increasedby 36% and 22%, respectively, when compared to mean baseline values of 1.5 REM periods per hour and 4.3 min/REM episode. Similar changeswere seen in the 100 pg, 500 l.(g and 1000 ,ug GH groups. SWSshowed a nonsignificant increase(up to 5%) during the first 3 hr in the four GH groups which had elevated REM time. The increased percentageof REM sleep was thus taken at the expense of waking, although the decreasein wakefulnesswere not statistically significant. On hours 4-7 both the saline and GH groups tended to show decreased REM time, decreasedSWS and increased wakefulness.No effect of GH was apparent when comparedto the post-salinevalues for this time period. DISCUSSION The elevation in REM time for the first 3 hr after GH is significant in several respects.It is the only endogenously produced agent whose systemic administration has been reported to selectively increaseREM sleep (in certain instances direct brain injection of neurotransmitters increases REM sleepCordeau, Moreau, Beaulnes and Laurin, 1963; George, Haslett and Jenden, 1964). Since there is a large release of GH during SWS,at present assessed only in primates (Takahashi et al., 1968; Honda et al., 1969; Sassinet al., 1969) and since administration of exogenousGH increasedREM sleep,it may be that the normal endogenous release of GH during SWS in some way triggers the subsequent occurrence of REM sleep. Although we did not
SLEEPANDGROWTHHORMONE
193
determine the minimum effective dose of GH, GH did elevate REM time at a dose of about 1 X 10-l’ moles/kg (50 E.cgdose given to a 3 kg cat, molecular weight of 21,000; Santome, Dellacha and Paladini, 1968). The fact that GH in doses of 50-1000 pg produced equivalent effects of REM time suggests that once a certain level of GH is achieved, no additional enhancement of REM occurs with increasing amounts of GH. Since we did not measure plasma GH levels in our cats we do not know to what extent levels of GH in plasma mirrored the amount of GH injected intraperitoneally.
EXPERIMENT 2 Introduction
and Method
Human studies often show a lag of several hours between peak plasma GH values and the peak occurrence of REM sleep (Takahashi et al., 1968; Honda et ai., 1969; Sassin et al., 1969). We therefore determined whether introducing a similar lag in cats, namely by blocking the initial 3 hr increase in REM time, would abolish the GH effect (in the subsequent sleep period). Five cats employed in the first study were injected, ip, with IOOpg of bovine GH and were awakened from each REM episode during the first 3 hr postinjection. Arousals from REM periods were produced by monitoring the EEG and tapping on the recording chamber when the cat entered a REM episode. In control sessions the same five cats experienced 3 hr of REM disruption with prior saline injection. All cats were permitted to have undisturbed sleep in the period of 4-7 hr postinjection. Results and Discussion The results, given in Table 2, show that partial REM deprivation (REM dep.) was produced in the first 3 hr since there was a 60-70% reduction in REM time. Paired t-test (2-tailed) were used to compare the waking, SWS and REM sleep percentages of the REM dep. group to the GH plus REM dep. condition. The amount of REM sieep in hours 4-7 was significantly greater in the group pretreated with 1OOpg of GH. At this time there was a small and non-significant increase in SWS and non-significant decrease in waking time in the GH treated cats. Thus, when the REM elevating effect of GH is blocked for 3 hr an increase in REM time still occurs in the following 4 hr period-however, this postdeprivation increase is smaller than the elevation of REM sleep observed in Exp. 1 (which did not employ a postponement of GH effects). Perhaps a similar delay in the action of GH on REM sleep also occurs in man, i.e., SWS continues for 2-3 hr following peak plasma GH levels and then the increase in REM time occurs.
194
STERNET AL. TABLE 2 Elevation of REM Sleepby Growth HormoneAfter an Experimentally-Induced3 hr Delay Mean_+SE percentof recordingtime
Hr l-3 Waking% SWS% REM% Hr 4-7 Waking% SWS% REM%
100 ccgGH REM Dep. hr l-3 n=5
Baseline n=5
REM Dep. hr 1-3 n=5
36.4+8.9 49.6+6.3 13.8~3.1
41.4k4.1 54.ot4.1 4.821.6
42.4i8.4 53.3A7.3 4.4kl.l
45.6k7.6 38.6k6.0 15.422.1
40.422.2 39.8i3.2 19.U1.8
30.8+2.4* 43.3t3.6 25.6+2.0**
*p<.10. **p-C.05 comparisonsof REM dep. to GH plus REM dep.
General Discussion
In any multifaceted behavioral state the mechanism(s)which regulate its occurrence are complex. The present data support the view that increasedGH secretion may be one of a number of factors which enhancesREM sleep. In addition to the present studies, there are certain parallels between conditions associated with high plasma GH levels and high REM time. For example, in human infancy basal GH levels during waking and sleeping are much higher than during adulthood (average plasma GH levels in young infants during waking or sleep are 50 rig/ml or higher, Vigneri and D’Agata, 1971; Shaywitz, Finkelstein, Hellman and Weitzman, 1971-peak SWSvalues of plasmaGH in adults are 15-20 &ml, Takahashiet al., 1968 Honda et al., 1969). REM sleep percentages/24hr in infants typically average4-5 times that of normal adults (Roffwarg, Muzio and Dement, 1966). In old age,REM time often diminishes to less than half-that of young adult values (Roffwarg et al., 1966; Carlson, Gillin, Gorden and Snyder, 1972). This decreasein REM time is accompanied by a reduction or total absenceof the normal SWSreleaseof GH (Vigneri, D’Agata and Polosa, 1971; Carlson et al., 1972). This ontogenetic parallel between the secretion of GH and the occurrence of REM sleep in man is noteworthy since there have been no prior suggestions of a posssible mechanismwhich accounts for the well-known developmentalpattern of REM sleep.
SLEEP AND GROWTH HORMONE
195
One other aspect of the present findings concerns the question of whether GH directly affects the functioning of the central nervous system. Since GH exerts pronounced effects on other hormones, notably insulin (Altszuler, Steele, Rathgeb and DeBodo, 1968; Akerblom, Martin and Gary, 1973), as well as many metabolic processesin peripheral tissues(reviewed in Root, 1972), it is possible that the present elevation of REM sleep may not be due to direct action of GH on the brain. However, unpublished findings in our laboratory suggest that bovine GH exerts marked effects on protein synthesis and biogenic amine levels in cat and rat brain. Prior studies in the cat show that alterations in protein synthesis (Stern, Morgane, Panksepp, Zolovick and Jalowiec, 1972) or biogenic amine metabolism (reviewed in Jouvet, 1972) can produce marked changes in sleep-waking patterns. The present results suggestthat the role of GH in regulating sleep state occurrence and in the metabolism of the central nervous system merits further consideration.
REFERENCES Akerblom, H. D., Martin, .I. M., and Gary, G. L. (1973). Relative role of cortisone and growth hormone on glucose intolerance and insulin secretion in rat. Horm. Metab. Res. 5, 34-37. Altszuler, N., Steele, R., Rathgeb, I., and DeBodo, R. C. (1968). Influence of growth hormone on glucose metabolism and plasma levels in the dog. In A. Pecile and E. E. Muller (Eds.), Growth Hormone, pp. 309-318, Excerpta Medica Foundation, Amsterdam. Carlson, H. E., Gillin, J. C., Gorden, P., and Snyder F. (1972). Absence of sleep-related growth hormone peaks in aged normal subjects and in acromegaly. J. Clin. Endocrinol. Metab. 34, 1102-l 105. Cordeau, J. P., Moreau, A. P., Beaulnes, A., and Laurin, C. (1963). EEG and behavioral changes following microinjections of acetylcholine and adrenaline in the brain stem of cats. Arch. Ital. Biol. 101, 3047. Geschwind, I. I. (1967). Molecular variation and possible lines of evolution of peptide and protein hormones. Amer. Zool. 7, 89-108. George, R., Haslett, W. L., and Jenden, D. J. (1964). A choline@ mechanism in the brainstem reticular formation: Induction of paradoxical sleep. Intl. J. Neuropharmacol. 3, 541-552. Honda, Y., Takahashi, K., Takahaski, S., Azumi, K., Sakuma, M., Tsushima, T., and Shimizu, K. (1969). Growth hormone secretion during nocturnal sleep in normal subjects. J. Clin. Endocrinol. 29, 20-29. Jouvet, M. (1972). The role of monoamines and acetylcholine containing neurons in the regulation of the sleep-waking cycle. In Reviews of Physiology: Biochemistry and Experimental Pharmacology, pp. 168-307, Springer-Verlag, New York. Roffwarg, H., Muzio, J., and Dement, W. (1966). The ontogenetic development of the sleep-dream cycle in humans. Science 152,604-619. Root, A. W. (1972). Human Pituitary Growth Hormone, pp. 13-34. C. C Thomas, Springfield, IL.
196
STERN ET AL.
Santome, J. A., Dellacha, J. M., and Paladini, A. C. (1968). Structural studies on bovine growth hormone. In A. Pecile and E. E. Muller (Eds.), Growth Hormone, pp. 29-37, Excerpta Medica Foundation, Amsterdam. Sassin, J. F., 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 and sleep-waking cycles. Science 165,513-515. Shaywitz, B. A., Finkelstein, J., Hellman, L., and Weitzman, E. D. (1971). Growth hormone in new-born infants during wake-sleep periods. Pediatrics 48, 103-109. Stern, W. C., and Morgane, P. J. (1973). Effects of reserpine on sleep and brain biogenic amine levels in the cat. Psychopharmacologia 28,275-286. Stern, W. C., Morgane, P. J., Panksepp, J., Zolovick, A. J., and Jalowiec, J. E. (1972). Elevation of REM sleep following inhibition of protein synthesis. Bruin Rex 47, 254-258. Takahashi, Y., Kipnis, D. M., and Daughaday, W. H. (1968). Growth hormone secretion during sleep. J. Clin. Invest. 47, 2079-2090. Vigneri, R., and D’Agata, R. (1971). Growth hormone release during the first year of life in relation to sleep-wake periods. J. CZin. Endocrirzol. Metab. 33, 561-563. Viineri, R., D’Agata, R., and Polosa, P. (1971). Growth hormone secretion related to sleep at different ages in man: Chronobiological and physiological implications. I2 Progress0 Medico 27, 366-372. Winer, B. J. (1962). Statistical principles in Experimental Design, pp. 89-92, pp. 105-138. McGraw-Hill, New York.
AND BEHAVIOR,
Effects
WARREN
6, 189-196 (1975)
of Growth Hormone on Sleep-Waking Patterns in Cats’
C. STERN,
JOHN E. JALOWIEC, HARLAN and PETER J. MORGANE
SHABSHELOWITZ,
Worcester Foundation for Experimental Biology, Shrewsbury, Massachusetts 01.545
Cats given growth hormone in doses from 50-1000 pg, i.p., showed a selective elevation of REM sleep in the fist 3 hr postinjection. Bovine thyrotropin control injections did not alter sleep patterns. When the effect of growth hormone on sleep was blocked by REM deprivation for the first 3 hr, the REM elevating effect of growth hormone still occurred in the subsequent sleep period. These results suggest that growth hormone affects the central nervous system, either directly or indirectly. Also, the greatly increased secretion of growth hormone, which has been reported during slow-wave sleep in man, may play a role in the occurrence of REM sleep.
INTRODUCTION One fundamental characteristic of normal mammalian adult sleep cycles is that slow-wave sleep (SWS) always precedes the occurrence of rapid eye movement (REM) sleep. Since several investigators have reported that in man plasma growth hormone (GH) levels are markedly elevated during the period of the night occupied by SWS (Takahashi, Kipnis and Daughaday, 1968; Honda, Takahashi, Takahashi, Azumi, Sakuma, Tsushima and Shimtiu, 1969; Sassin, Parker, Mace, Gotlin, Johnson and Rossman, 1969) the possibility arises that GH secretion during SWS may play a role in the subsequent occurrence of REM sleep. We investigated this potential relationship by administering bovine GH to cats and recording the subsequent sleep-waking patterns. Bovine GH is biologically active in cats as shown by stimulation of there has been no examination of growth (Geschwind, 1967). However, whether pituitary GH is released during SWS in the cat as occurs in man.
IThis research was supported by grants MH 02211, MH 10625, HD 06364 and by funds from the Worcester Foundation for Experimental Biology.
189 Copyright @ 1975 by Academic Press, Inc. All rights of reproduction in any form reserved.
190
STERN ET AL.
EXPERIMENT 1 Method
Seven adult female cats (Fauna Laboratories, Hudson, MA) were inplanted with electrodes for recording EEG activity of the cortex (frontal and occipital poles), hippocampus, lateral geniculate nucleus (LGN), and neck EMG and eye movements. They were housed on a 12: 12 1ight:dark cycle (0700-1900 hr lights on) with ad lib. accessto food and water. Starting at least one week after surgery each cat received three to five 7 hr baseline polygraphic recording sessions using the apparatus, recording and scoring (waking, SWS, REM sleep) procedures described by Stern and Morgane (1973). Briefly, the cats were placed in an electrically shielded, sound attenuated room and connected to Grass instrument polygraphs using a counter-weighted slip-ring cable system which allowed free movement. With respect to EEG scoring, waking was characterized by a low voltage cortical EEG, high neck muscle tonus and occasional bursts of eye movements and hippocampal theta rhythm (4-7 cycles/set). SWS was identified by a high voltage, low frequency cortical and hippocampal EEG, no eye movementsand low muscle tonus. REM sleep consisted of an activated cortical EEG, continual hippocampal theta rhythm, bursts of eye movements,neck muscle atonia and monophasic spiking in the EEG of the LGN channel. Then, at the start of either a saline (0.9%) vehicle, bovine thyrotropin or bovine GH (both hormones obtained from Calbiochem, San Diego, CA). Thyrotropin and GH were dissolved in saline. The GH doses given in random order to each cat were: 1000, 500, 100, 50, and 0.5 or 0.051.rg-two cats also received a 3OOOpg dose (each dose given once per cat). The saline injections were randomly interspersedbetween the GH sessions.Both bovine growth hormone and thyrotropin are polypeptide hormones of similar molecular weight, about 21,000. The thyrotropin control injections were given after the GH injection seriesand were 100 and SOOpg. RESULTS Table 1 shows the effects of bovine GH injection on sleep-waking percentages.The results are divided into two time periods-the first 3 hr postinjection and the subsequent4 hr. This was done since the REM ebvating effects of GH occurred for about 3 hr. Baselinevalues represent the meansof 3-5 sevenhr recording sessionsfor each cat. Statistical comparisonsof baseline vs. postinjection scores were made using analyses of variance with repeated measuresfor each of the rows in Table 1 and the studentized range statistic for the post hoc tests (Winer, 1962). The standard errors in Table 1 are based on between subject data, whereas the statistical analysis was within subjects.
*p< .05, 2-tailed.
1000 /.Jg
0.05-0.5 pg 50% 100 Pg 5OO!Jg
Growth hormone
500/G
Baseline Saline Thyrotropin 50/G
4 7 7 7 7
48,0?5 29.6*7 36.4t8 34.3+8 33.0?8
38.2*8 38.9*8
6 5
7
42.028 39.9+ 10
Wake
7
n
43.1?4 51.5*4 46.0?6 49.1+5 50.1*5
51.6+5 49.1+6
46.6+5 46.3~7
SWS
hr l-3
9.lt8 18.6*8* 17.6?8* 17.1*8* 16.4+7*
10.2+5 12.0t4
11.3*5 13.9a6
REM
61.2+5* 62.7*7* 59.6t5 65.4?6* 59.0+7
66.1+12 60.8*14
45.357 61.0+8*
Wake
Mean f SE percent of recording time
26.4+1* 28.3t4 30.1+4 24.4?5* 30.156
21.6+9 31.8211
39.1+4 28.4*6
sws
hr 4-l
Effects of Bovine Growth Hormone and Thyrotropin on Sleep-Waking Percentages in Cats.
TABLE 1
12.2*2 9.052 10.7+2 10.1-?2 10.6+2
6.4+3 8.4+3
15.3*3 10.4t3
REM
5 3
$
2 Ei
u $
%
8
F
192
STERN ET AL.
The results show that in the first 3 hr following GH injection REM time was significantly elevated by 50% above baseline at the 50, 100, 500 and 1000 @gdoses.Dosesabove or below this range did not increaseREM sleep (2 cats received a dose of 3000 pg of GH and showed mainly waking behavior for the next 7 hr). Interestingly, the REM elevating effects of the 50-1000 pg dosesof GH were essentially the same.The maximum increasein the amount of REM sleep in the first 3 hr occurred in the 50 pg group, with an elevation from 11.3% of recording time during baselineto 18.6%after GH. In comparison to the saline injected group, which showed a nonsignificant rise in REM time, the 50-104lOMggroups (pooled) showed a significant increase beyond the saline effect of 3.6% of recording time Cp< .Ol, 2-tailed test). The thyrotropin controls showed no appreciable change in the percentages or latencies of REM, SWSor waking. An example of the effects of GH on REM latencies, REM length and number of REM periodslhr within the first 3 hr post-GH is found in the results of the 50 pg group. This group showed a latency to the first REM period of 47 f 8 min (mean + SE) compared to baseline latencies of 74 + 11 min 0, < .Ol, 2-tailed t-test). SWSlatencies did not change significantly (post-GH latency of 25 + 9 min, baseline latency of 34 ?I 10 min). After 50 pg of GH the REM periods/hr and length of the averageREM episode increasedby 36% and 22%, respectively, when compared to mean baseline values of 1.5 REM periods per hour and 4.3 min/REM episode. Similar changeswere seen in the 100 pg, 500 l.(g and 1000 ,ug GH groups. SWSshowed a nonsignificant increase(up to 5%) during the first 3 hr in the four GH groups which had elevated REM time. The increased percentageof REM sleep was thus taken at the expense of waking, although the decreasein wakefulnesswere not statistically significant. On hours 4-7 both the saline and GH groups tended to show decreased REM time, decreasedSWS and increased wakefulness.No effect of GH was apparent when comparedto the post-salinevalues for this time period. DISCUSSION The elevation in REM time for the first 3 hr after GH is significant in several respects.It is the only endogenously produced agent whose systemic administration has been reported to selectively increaseREM sleep (in certain instances direct brain injection of neurotransmitters increases REM sleepCordeau, Moreau, Beaulnes and Laurin, 1963; George, Haslett and Jenden, 1964). Since there is a large release of GH during SWS,at present assessed only in primates (Takahashi et al., 1968; Honda et al., 1969; Sassinet al., 1969) and since administration of exogenousGH increasedREM sleep,it may be that the normal endogenous release of GH during SWS in some way triggers the subsequent occurrence of REM sleep. Although we did not
SLEEPANDGROWTHHORMONE
193
determine the minimum effective dose of GH, GH did elevate REM time at a dose of about 1 X 10-l’ moles/kg (50 E.cgdose given to a 3 kg cat, molecular weight of 21,000; Santome, Dellacha and Paladini, 1968). The fact that GH in doses of 50-1000 pg produced equivalent effects of REM time suggests that once a certain level of GH is achieved, no additional enhancement of REM occurs with increasing amounts of GH. Since we did not measure plasma GH levels in our cats we do not know to what extent levels of GH in plasma mirrored the amount of GH injected intraperitoneally.
EXPERIMENT 2 Introduction
and Method
Human studies often show a lag of several hours between peak plasma GH values and the peak occurrence of REM sleep (Takahashi et al., 1968; Honda et ai., 1969; Sassin et al., 1969). We therefore determined whether introducing a similar lag in cats, namely by blocking the initial 3 hr increase in REM time, would abolish the GH effect (in the subsequent sleep period). Five cats employed in the first study were injected, ip, with IOOpg of bovine GH and were awakened from each REM episode during the first 3 hr postinjection. Arousals from REM periods were produced by monitoring the EEG and tapping on the recording chamber when the cat entered a REM episode. In control sessions the same five cats experienced 3 hr of REM disruption with prior saline injection. All cats were permitted to have undisturbed sleep in the period of 4-7 hr postinjection. Results and Discussion The results, given in Table 2, show that partial REM deprivation (REM dep.) was produced in the first 3 hr since there was a 60-70% reduction in REM time. Paired t-test (2-tailed) were used to compare the waking, SWS and REM sleep percentages of the REM dep. group to the GH plus REM dep. condition. The amount of REM sieep in hours 4-7 was significantly greater in the group pretreated with 1OOpg of GH. At this time there was a small and non-significant increase in SWS and non-significant decrease in waking time in the GH treated cats. Thus, when the REM elevating effect of GH is blocked for 3 hr an increase in REM time still occurs in the following 4 hr period-however, this postdeprivation increase is smaller than the elevation of REM sleep observed in Exp. 1 (which did not employ a postponement of GH effects). Perhaps a similar delay in the action of GH on REM sleep also occurs in man, i.e., SWS continues for 2-3 hr following peak plasma GH levels and then the increase in REM time occurs.
194
STERNET AL. TABLE 2 Elevation of REM Sleepby Growth HormoneAfter an Experimentally-Induced3 hr Delay Mean_+SE percentof recordingtime
Hr l-3 Waking% SWS% REM% Hr 4-7 Waking% SWS% REM%
100 ccgGH REM Dep. hr l-3 n=5
Baseline n=5
REM Dep. hr 1-3 n=5
36.4+8.9 49.6+6.3 13.8~3.1
41.4k4.1 54.ot4.1 4.821.6
42.4i8.4 53.3A7.3 4.4kl.l
45.6k7.6 38.6k6.0 15.422.1
40.422.2 39.8i3.2 19.U1.8
30.8+2.4* 43.3t3.6 25.6+2.0**
*p<.10. **p-C.05 comparisonsof REM dep. to GH plus REM dep.
General Discussion
In any multifaceted behavioral state the mechanism(s)which regulate its occurrence are complex. The present data support the view that increasedGH secretion may be one of a number of factors which enhancesREM sleep. In addition to the present studies, there are certain parallels between conditions associated with high plasma GH levels and high REM time. For example, in human infancy basal GH levels during waking and sleeping are much higher than during adulthood (average plasma GH levels in young infants during waking or sleep are 50 rig/ml or higher, Vigneri and D’Agata, 1971; Shaywitz, Finkelstein, Hellman and Weitzman, 1971-peak SWSvalues of plasmaGH in adults are 15-20 &ml, Takahashiet al., 1968 Honda et al., 1969). REM sleep percentages/24hr in infants typically average4-5 times that of normal adults (Roffwarg, Muzio and Dement, 1966). In old age,REM time often diminishes to less than half-that of young adult values (Roffwarg et al., 1966; Carlson, Gillin, Gorden and Snyder, 1972). This decreasein REM time is accompanied by a reduction or total absenceof the normal SWSreleaseof GH (Vigneri, D’Agata and Polosa, 1971; Carlson et al., 1972). This ontogenetic parallel between the secretion of GH and the occurrence of REM sleep in man is noteworthy since there have been no prior suggestions of a posssible mechanismwhich accounts for the well-known developmentalpattern of REM sleep.
SLEEP AND GROWTH HORMONE
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One other aspect of the present findings concerns the question of whether GH directly affects the functioning of the central nervous system. Since GH exerts pronounced effects on other hormones, notably insulin (Altszuler, Steele, Rathgeb and DeBodo, 1968; Akerblom, Martin and Gary, 1973), as well as many metabolic processesin peripheral tissues(reviewed in Root, 1972), it is possible that the present elevation of REM sleep may not be due to direct action of GH on the brain. However, unpublished findings in our laboratory suggest that bovine GH exerts marked effects on protein synthesis and biogenic amine levels in cat and rat brain. Prior studies in the cat show that alterations in protein synthesis (Stern, Morgane, Panksepp, Zolovick and Jalowiec, 1972) or biogenic amine metabolism (reviewed in Jouvet, 1972) can produce marked changes in sleep-waking patterns. The present results suggestthat the role of GH in regulating sleep state occurrence and in the metabolism of the central nervous system merits further consideration.
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