Effect of phenobarbital on sleep and nighttime plasma growth hormone and cortisol levels.

The acute and chronic effects of phenobarbital and phenobarbital withdrawal on sleep patterns and on plasma growth hormone (GH) and cortisol fluctuations occurring during sleep were studied. Before bed, five healthy men, aged 21 to 25, were given a placebo on three baseline nights, phenobarbital (100 mg p.o.) for nine nights, and a placebo on a final withdrawal night. Beginning on the third of three consecutive nights in the laboratory, all-night polygraphic sleep recordings and blood samples (obtained every 20 min through indwelling venous cannulae) were collected for the placebo, acute phenobarbital, chronic phenobarbital, and phenobarbital withdrawal conditions. Blood phenobarbital levels ranged between 5 to 9 micrograms/100 mL across all hours of the chronic drug night. At this low sedative dose, latency to sleep onset and stage 4 sleep were significantly reduced in the chronic drug condition, but REM sleep was not significantly reduced. No significant sleep change was observed on the withdrawal night. Both peak GH level and total integrated GH across the night were unaffected by the acute, chronic, and withdrawal conditions. The pattern of GH release appeared to be altered on the phenobarbital and phenobarbital withdrawal nights as compared with placebo. Nighttime plasma cortisol levels were not significantly altered by any experimental condition.