Synchronizing effect of the alpha 1-adrenoceptor agonist 2-(2-chloro-5-trifluoromethylphenylimino)imidazolidine on rabbit electroencephalogram.

The selective alpha 1-adrenoceptor agonist St 587 (2-(2-chloro-5-trifluoromethylphenylimino)imidazolidine) was tested in conscious rabbits in the dose range of 0.125 to 8 mg/kg cumulatively i.v. In cardiovascular experiments St 587 increased mean arterial blood pressure and decreased heart rate in a dose dependent manner. In neuropharmacological experiments St 587 induced a biphasic EEG effect, an EEG synchronization preceded by a short period of cortical arousal. The duration of both EEG phenomena increased with increasing doses. There was no correlation between rise in blood pressure and EEG arousal reaction as periods of precentral spindling appeared also during maximal increase in blood pressure. Both, EEG synchronization and arousal reaction could be antagonized by the alpha 1-adrenoceptor antagonist prazosin, 1-2 mg/kg i.v. From these experiments it is concluded that the main effect of the alpha 1-adrenoceptor agonist St 587 in rabbits is EEG synchronization, i.e. sedation. Furthermore a barbiturate antagonism by high doses of St 587 was shown and this is explained by the initial arousal reaction as observed after injection of St 587.