Growth hormone secretion during long-term thiopental anesthesia in the immature rat.

The secretory pattern of growth hormone (GH) in 29 to 31 day old immature rats during long-term thiopental anesthesia was studied. Individual GH secretory profiles were determined by sequential blood sampling at 10 min intervals for 6.0 hr starting from about 1.0-1.5 hr after the onset of thiopental administration. EEG was concurrently monitored throughout the experimental period, and the animals were maintained in stable patterns. GH levels in whole blood samples were determined by radioimmunoassay and were subjected to analysis by power spectrum and least-squares methods. The results showed that all 25 immature rats exhibited episodic secretion of GH. Twenty-four of them (96%) showed GH surges occurring with periodicities within the mean +/- 2SD range for the results from unanesthetized, sham-operated animals. The mean periodicity for the 25 animals was 3.25 +/- 0.12 (SE) hr. The results suggest that the rhythmicity of GH secretion observed in the freely-moving condition is maintained during anesthesia.