Blockade of acetylcholine receptors does not change the dose of etomidate required to produce immobility in rats.
BACKGROUND
Administration of drugs blocking muscarinic plus neuronal nicotinic acetylcholine receptors (e.g., atropine and mecamylamine) does not affect the MAC of isoflurane. Although this implies that acetylcholine receptors do not mediate the immobility produced by inhaled anesthetics, another interpretation is possible. Sub-MAC concentrations of isoflurane alone profoundly block acetylcholine receptors, allowing for the possibility that atropine and mecamylamine have no effect because the receptors already are blocked.


METHODS
In the present study, we indirectly tested this possibility by measuring the capacity of acetylcholine receptor blockade to decrease the anesthetic requirement for etomidate, an anesthetic thought to act solely by enhancing the effect of gamma-aminobutyric acid on gamma-aminobutyric acid(A) receptors.


RESULTS
Administration of 10 mg/kg atropine plus 5 mg/kg mecamylamine did not change the infusion rate of etomidate, or the blood or brain concentrations of etomidate required to produce immobility in rats.


CONCLUSIONS
Acetylcholine receptors do not mediate the capacity of anesthetics to produce immobility in the face of noxious stimulation.
Zhang
Yi
Y
Department of Anesthesia and Perioperative Care, University of California, San Francisco, California 94143-0464, USA.
Laster
Michael J
MJ
Eger
Edmond I
EI
Sharma
Manohar
M
Sonner
James M
JM
D018686:Anesthetics, Intravenous / Q000494:pharmacology*; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D005045:Etomidate / Q000494:pharmacology*; D007103:Immobilization; D008297:Male; D008464:Mecamylamine / Q000494:pharmacology; D009043:Motor Activity / Q000187:drug effects*; D018727:Muscarinic Antagonists / Q000494:pharmacology; D018733:Nicotinic Antagonists / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011950:Receptors, Cholinergic / Q000187:drug effects*; D011963:Receptors, GABA-A / Q000187:drug effects; D011976:Receptors, Muscarinic / Q000187:drug effects; D011978:Receptors, Nicotinic / Q000187:drug effects
D018686:Anesthetics, Intravenous; D018727:Muscarinic Antagonists; D018733:Nicotinic Antagonists; D011950:Receptors, Cholinergic; D011963:Receptors, GABA-A; D011976:Receptors, Muscarinic; D011978:Receptors, Nicotinic; D008464:Mecamylamine; D001285:Atropine; D005045:Etomidate