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.

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 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 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.