Neurophysiological investigation of the central nervous action of the hypnotic agent etomidate in cats (author's transl)]

1. The action of etomidate (0.125-4.0 mg/kg) injected intravenously or into the right atrium (time of injection about 1 sec) was investigated in cats under different central nervous conditions. 2. In decerebrate unanaesthetized animals and in lightly anaesthetized (pentobarbitone) animals with an intact CNS etomidate (0.25-4 mg/kg i.v.) caused a decrease of the spontaneous lumbar fusimotor activity and a strong depression of the fusimotor pinnareflex. Partly a reversal of this reflex from excitation to inhibition was observed. The effects occurred within 20 sec after the injection and lasted for 5-70 min, showing a clear non-linear relationship with the injected dose. 3. In encephale isole preparations etomidate (0.125-1 mg/kg injected intra-right atrially) caused distinct changes of the spontaneous EEB (decrease of frequency, increase of amplitude, occurrence of steeper waves) and a depression of the arousal reactions in the EEB following different stimuli (acoustic stimuli and different stimuli in the area of the face and eyes). These effects occurred within 8 sec after the injection and lasted up to 40 min, dependent upon the injected dose. 4. The character and the principal similarity of the results observed in decerebrate animals and in animals with intact CNS suggest that a considerable part of the action of etomidate consists of a depression of the activity and reactivity of the brain stem reticular formation.