Effects of isoeugenol on in vitro neuromuscular blockade of rat phrenic nerve-diaphragm preparations.
OBJECTIVE
To investigate in vitro effects of isoeugenol on neuromuscular transmission in tissues obtained from rats.


METHODS
Tissues (phrenic nerve and diaphragm) obtained from 15 male Sprague-Dawley rats.


METHODS
Rats were euthanatized, and tissues (phrenic nerves and diaphragm) were obtained. Phrenic nerve-diaphragm preparations were examined in vitro. The phrenic nerve was stimulated with weak electrical impulses. Muscle-twitch responses were recorded before and after the addition of drugs (pancuronium, neostigmine, isoeugenol, and benzocaine).


RESULTS
Pancuronium and isoeugenol in low concentrations (10 to 206 microM) caused a distinct decrease in twitch response, which could be reversed by the addition of neostigmine. The decrease in twitch response caused by benzocaine or high concentrations of isoeugenol could not be reversed by the addition of neostigmine.


CONCLUSIONS
Isoeugenol caused a competitive blockade of neuromuscular transmission. Neostigmine restored this transmission by inhibiting acetylcholinesterase, which led to increased concentrations of acetylcholine. Because isoeugenol is used as an anesthetic in fish, further investigations are necessary to determine whether fish exposed to isoeugenol are sedated and unconscious or whether they are only paralyzed but have intact perception in afferent sensory nerves.
Ingvast-Larsson
J Carina
JC
Department of Pharmacology and Toxicology, Faculty of Veterinary Medicine, Swedish University of Agricultural Sciences, Uppsala.
Axén
V Charlotte
VC
Kiessling
Anders K
AK
D000779:Anesthetics, Local / Q000494:pharmacology; D000818:Animals; D001566:Benzocaine / Q000494:pharmacology; D003964:Diaphragm / Q000187:drug effects* / Q000294:innervation*; D004359:Drug Therapy, Combination; D005054:Eugenol / Q000031:analogs & derivatives* / Q000494:pharmacology*; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009388:Neostigmine / Q000494:pharmacology; D019148:Neuromuscular Blockade; D003473:Neuromuscular Nondepolarizing Agents / Q000494:pharmacology; D010197:Pancuronium / Q000494:pharmacology; D010791:Phrenic Nerve / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley
D000779:Anesthetics, Local; D003473:Neuromuscular Nondepolarizing Agents; D009388:Neostigmine; D005054:Eugenol; C036643:isoeugenol; D010197:Pancuronium; D001566:Benzocaine