Sleep and Rhythms Projects

Acute hyperammonaemia induces a sustained decrease in vigilance, which is modulated by caffeine.

Casula EP, Bisiacchi PS, Corrias M, Schiff S, Merkel C, Amodio P, Montagnese S.
Metabolic Brain Disease
Hyperammonaemia is observed after prolonged, intense exercise, or in patients with hepatic failure. In the latter, it is associated with a set of neurological and psychiatric abnormalities termed hepatic encephalopathy.
1. to measure vigilance in a condition of induced hyperammonaemia; 2. to assess whether caffeine modulates the effects of hyperammonaemia on vigilance, if any. Ten healthy volunteers (28.5 ± 5 years; 5 males) underwent three experimental sessions consisting of two-hourly measurements of capillary ammonia, subjective sleepiness (Karolinska Sleepiness Scale) and vigilance (Psychomotor Vigilance Task, PVT), in relation to the intake of breakfast (+/-coffee), an amino acid mixture which induces hyperammonaemia (amino acid challenge; AAC), and AAC+coffee (only for participants who had coffee with their standard breakfast). The AAC resulted in: 1. the expected increase in capillary ammonia levels, with highest values at approximately 4 h after the administration; 2. a significant increase in subjective sleepiness ratings; 3. a sustained increase in PVT-based reaction times. When caffeine was administered after the AAC, both subjective sleepiness and the slowing in RTs were significantly milder than in the AAC-only condition. In conclusion, acute hyperammonaemia induces an increase in subjective sleepiness and a sustained decrease in vigilance, which are attenuated by the administration of a single espresso coffee.


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