We investigated the effect of adenosine on hypnosis induced by thiopen
tone, propofol and midazolam in mice. The onset and duration of hypnos
is were determined by the loss of righting reflex. Adenosine and 2-chl
oroadenosine caused a significant shortening of onset of sleep-time an
d prolongation of duration of sleep-time in all groups (p < 0.05). Dip
yridamole administration before combined intravenous anaesthetic-adeno
sine or intravenous anaesthetic-2-chloroadenosine administration produ
ced similar effects to adenosine (p < 0.05). The adenosine antagonist
theophylline, given before intravenous anaesthetic-adenosine or intrav
enous anaesthetic-2-chloroadenosine administration caused a significan
t delay in onset of sleep-time and shortening in the duration of sleep
-time (p < 0.05). We conclude that central excitatory noradrenergic ne
urones play an important role in adenosine, 2-chloroadenosine and dipy
ridamole-induced hypnotic responses to intravenous anaesthetics and th
eir inhibition by adenosine antagonists.