Effects of isoeugenol on in vitro neuromuscular blockade of rat phrenic nerve-diaphragm preparations

Abstract

Objective—To investigate in vitro effects of
isoeugenol on neuromuscular transmission in tissues
obtained from rats.

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

Procedure—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 206µM) 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 and Clinical Relevance—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.
(Am J Vet Res 2003;64:690–693)