Correlation of growth hormone secretion to sleep in the immature rat.

Abstract

SUMMARY1. The correlation between growth hormone (GH) secretion and the sleepwakefulness cycle in the 29-31 day-old male rat was studied by serial blood sampling through an intracardiac cannula at 10 min intervals from 12.00 to 18.00 h. E.e.g.s recorded continuously during the blood sampling period were scored into wakefulness and sleep, and the amount of sleep for every 10 min was plotted against the GH value as assessed by radioimmunoassay.2. The power spectrum analysis and the least-squares method applied to the time series of GH concentrations in the control rat, revealed that the mean periodicity was 3-12 + 0-09 h (mean+ S.E. of the mean) in fourteen rats examined.3. For the animals in which the e.e.g. was recorded simultaneously with blood samplings, the cross-correlation analysis performed between the time series of the amount of sleep and the GH value revealed a significant positive correlation between the GH level and the amount of sleep during the preceding 10 min.4. The time series of the sleep amount and the GH value had mean periodicities of3 09 + 0-17 and 3 05 + 0-13 h (mean + S.E. ofthe mean), respectively, in twenty-seven rats examined.5. Sleep deprivation performed between 13.00 and 15.00 h was effective in preventing GH secretary bursts which otherwise should appear during this time period of the day.6. Corticosterone measurement by protein-binding assay revealed that the procedure of sleep deprivation did not act as the 'stress' which has been known to inhibit GH secretion in the rat.7. These findings indicate that GH secretion in the rat is sleep-related, as has been proved in the human.

Relationship between the three‐hour‐period sleep‐wakefulness cycle and growth hormone secretion in the immature rat.

“…During the 6-h period the hematocrit fell by 20 %, but on the basis of our experience described previously (Kimura & Kawakami, 1982;Kawakami et al 1983) there seemed to be no significant effect on the health of the rat or on the weight gain afterwards. Further, this loss of blood was presumed not to be stressful for the rat, since GH secretion has been shown to be suppressed by stress (Kokka, Garcia, George & Elliott, 1972;Terry, Saunders, Audet, Willoughby, Brazeau & Martin, 1977), whereas secretion continued through the 6-h sampling period in immature rats (Kawakami et al 1983).…”

“…In a recent study using immature male rats, however, we obtained findings showing that bursts of GH secretion were synchronized with a sleep cycle which manifested an ultradian rhythm of approximately 3-0-h periodicity (Kimura & Kawakami, 1981;Kawakami et al 1983). It was indicated that the ultradian rhythm of the sleep-wakefulness cycle played a significant role in the regulation of GH secretion in the immature rat.…”

“…Recently, Eden and co-workers have reported that the GH was secreted episodically, with 2-4-h intervals throughout a 24-h period in rats older than 20 days of age and a synchronization of the secretary episodes was observed during the period between 09.00 and 15.00 h (Eden, Albertsson-Wikland & Isaksson, 1978;Eden, 1979). In the most recent study (Kawakami, Kimura & Tsai, 1983), we have analysed the time series of GH concentrations in the blood over the period between 12.00 and 18.00 h for the periodicity of GH secretary episodes, and found it to be approximately 3 0 h in the 29-31-day-old male rat. Those findings on the prepubertal rat seem to indicate the development of a 3-0-h-period ultradian rhythm of GH secretion by 30 days of age.…”

“…Further, this loss of blood was presumed not to be stressful for the rat, since GH secretion has been shown to be suppressed by stress (Kokka, Garcia, George & Elliott, 1972;Terry, Saunders, Audet, Willoughby, Brazeau & Martin, 1977), whereas secretion continued through the 6-h sampling period in immature rats (Kawakami et al 1983). …”

Detailed profile of prolactin secretion in the immature female rat: Evidence for the existence of an ultradian rhythm.

“…In the immature rat, we have also demonstrated that the rhythm was linked to the time of day ; i.e., the secretory episode of GH occurred eight times a day around 03.00, 06.00, 09.00, 12.00, 15.00, 18.00, 21.00 and 24.00 h. A quite interesting fact discovered in the present experiment is that the PRL secretory episode seems to occur in almost the same time schedule as that for the GH secretory episode. Since it was shown that the GH secretory episode coincided with the sleep cycle in the immature rat (Kawakami et al, 1983a), it is possible that PRL secretion also coincides with sleep. Experiments on this are currently under way.…”