The Interaction between Atropine and some Lipid‐soluble Barbiturates in Rats

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Abstract
The effect of atropine pretreatment on the CNS sensitivity to 5 lipid-soluble barbiturates was studied in rats. Atropine in a dose of 8 mg/kg i.p. or saline was given 1.5 h before an EEG-threshold determination with the tested barbiturates. The barbiturate was infused by constant rate through a tail vein. The dose of barbiturate needed to induce a burst suppression period in the EEG which is 1 s or longer was used as the threshold dose. Atropine prepreatment decreased the threshold dose significantly for 2 N-methylated barbiturates, hexobarbital (enhexymal NFN) and methohexital (enallynymal NFN), but not for thiopental (thiomebumal NFN), pentobarbital (mebumal NFN) or amobarbital (pentymal NFN). No clear effects of atropine pretreatment could be found in the ensuing anesthesia times after threshold determinations. Evidently, there are differences in mechanims of action between barbiturates. One of these mechanisms is related to the cholinergic system in the CNS.