Central administration of the somatostatin analog octreotide induces captopril-insensitive sleep responses

The effects of intracerebroventricular injections of the long-lasting somat ostatin analog octreotide (Oct) were studied on sleep and behavior in rats. Pyrogen-free physiological saline and Oct (0.001, 0.01, 0.1 mu g) or vehic le were administered at light onset, and the electroencephalogram (EEG), mo tor activity, and cortical brain temperature were recorded during the 12-h light period. Plasma growth hormone (GH) concentrations were measured in sa mples taken at 30-min intervals after Oct. Oct (0.01 and 0.1 mu g) suppress ed non-rapid eye movement sleep (NREMS) for 1-2 h. NREMS intensity (delta E EG activity during NREMS) dose dependently increased in hour 3 postinjectio n and thereafter (0.1 mu g). Plasma GH concentrations were suppressed after Oct (0.01 and 0.1 mu g), but pulses of GH secretions occurred 90-120 min p ostinjection in each rat. Oct (0.1 mu g) enhanced behavioral activity, incl uding prompt drinking followed by grooming, scratching, and feeding. Intrac erebroventricular injection of the angiotensin-converting enzyme inhibitor captopril (30 mu g, 10 min before Oct), blocked these behavioral responses but not the Oct-induced sleep alterations. The changes in sleep after intra cerebroventricular Oct suggest an intracerebral action site and might resul t from Oct-induced variations in the sleep-promoting activity of OH-releasi ng hormone.