Ultradian rhythm of growth hormone secretion and sleep in the adult male rat.

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Abstract
The correlation between growth hormone (GH) secretion and the sleep-wakefulness cycle in the adult male rat was studied by serial blood sampling at 10 min intervals. EEG recorded continuously during the blood sampling 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. 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 (.+-. S.E. of the mean) periodicity was 2.93 .+-. 0.10 h for the period from 0000-1200 h in 5 rats and 2.85 .+-. 0.06 h for the period from 1200-2400 h in 8 rats. For the animals in which the EEG was recorded simultaneously with blood samplings from 1200-2400 h, the cross-correlation analysis performed between the time series of the amount of sleep and the GH value revealed a significant positive correlation at time lags of 0-10 min in 6, and at time lags of 20-50 min in 4 of 14 cats. The number of animals having a positive correlation at short time lags seemed relatively less, but in most animals there was observed a definite relationship that each GH peak occurred with a consistent time lag ranging from 40-70 min following the onset of sleep cycle. Sleep deprivation performed from 1300-1600 h during the sampling period from 1100-1900 h was effective in preventing high-level GH pulses which otherwise should appear during this time of the day. Concurrent measurements of corticosterone concentrations in the sleep-deprivation experiment revealed that peak values of corticosterone secretory episodes were not influenced by sleep deprivation. The GH secretion in the adult rat is also correlated with the sleep-wakefulness cycle, although somewhat differently from the immature rat.