Circadian rhythm of rectal temperature during sleep deprivation with modafinil.

Background: Sleep deprivation (SD) induces many adverse psychological and physiological effects, particularly on vigilance and the thermoregulatory system. The drug modafinil appears to suppress or diminish the harmful effects on vigilance. However, the effects of modafinil combined with SD on the circadian rhythm of core temperature are not well established.

Hypothesis: We studied the circadian rhythm of rectal temperature (CRTre) during 62 h of SD alone or with three dosage levels of modafinil.

Methods: Six men underwent repeated SD experiments lasting 7 d each, including a 24-h control period, 62 h of SD, and a 24-h recovery period. Experiments were repeated four times in mixed order for placebo and three levels of modafinil (50, 150, or 300 mg x 24 h(-1)). The Tre was recorded each minute throughout the experiment and the CRTre was studied by the single cosinor method.

Results: Independent of modafinil, SD increased the mesor (p < 0.05) and reduced the amplitude (p < 0.01) of the CRTre without changing the acrophase. During the recovery period, a rebound increase was seen in the amplitude of the CRTre (p < 0.01). The 50 mg x 24 h(-1) dose of modafinil, but not the higher doses, induced a lower mesor (p < 0.01) independent of SD.

Conclusions: The observed changes may reflect a threshold for the central action of modafinil on core temperature. The hyperthermic effect reported in the literature for SD with modafinil may actually result from the sleep deprivation alone.