Corticosterone and growth hormone secretions during long-term thiopental anesthesia in the male rat.

To study the temporal correlation of secretory profiles of corticosterone (CS) and growth hormone (GH) in adult male rats in the continuous-sleep state, CS and GH concentrations were measured in blood sampled at 10-min intervals through an intracardiac cannula for 11-12 h under long-term thiopental anesthesia. The cortical electroencephalogram (EEG) was monitored to maintain stable sleep during the sampling period. Sixteen rats were subjected to the experiment. By analysis of power spectrum and least-squares methods all the time series of CS and GH concentrations in blood were revealed to have three major ultradian rhythms with periodicities of 1.5 h and its multiples. Although there were no significant positive or negative cross-correlation coefficients between the periodicities of CS and GH, a tendency was evident for GH concentrations to be high when CS concentrations were low, and CS concentrations to be high when GH concentrations were low. The results demonstrate that CS and GH secretions are able to manifest the same ultradian rhythms as those in the unanesthetized, freely moving condition even in the continuous-sleep state due to thiopental anesthesia. Combined with our previous findings, the CS, GH and sleep-wakefulness rhythms appear to be governed by separate pacemakers, although sharing the same basic ultradian rhythm.