J Korean Pain Soc.  1999 Nov;12(2):177-182.

Effect of Adrenergic Receptors on the Nerve Conduction in Rat Sciatic Nerves

• Lee C
• Jung SY
• Choi Y
• Leem JW
• Leem HS
• Yang HC
• Han SM
• Kong HS
• Lim SW

Abstract

BACKGROUND: Clonidine, an a adrenergic agonist blocks nerve conduction. However, in our previous experiment we found that adrenaline neither blocks nerve conduction by itself nor augment nerve conduction blockade by lidocaine near clinical concentrations. Possible explanations are: 1) there may be antagonism between some of adrenergic receptors, 2) clonidine may block nerve conduction via non-adrenergic mechanism. The purpose of this study is to obtain dose-response curves of several different forms of adrenergic receptor agonist to see the relative potencies of each adrenergic receptors to block nerve conduction.
METHODS
Recordings of compound action potentials of A-fiber components (A-CAPs) were obtained from isolated sciatic nerves of adult male Sprague-Dawley rats. Nerve sheath of the sciatic nerve was removed and desheathed nerve bundle was mounted on a recording chamber. Single pulse stimuli (0.5 msec, supramaximal stimuli) were repeatedly applied (2Hz) to one end of the nerve and recordings of A-CAPs were made on the other end of the nerve. Dose-response curves of epinephrine, phenylephrine, isoproterenol, clonidine were obtained.
RESULTS
ED50 of each adrenergic agonist was: 4.51 x 10(-2)M for epinephrine; phenylephrine, 7,74 x 10(-2)M; isoproterenol, 9.61 x 10(-2)M; clonidine, 1.57 x 10(-3)M.
CONCLUSION
This study showed that only clonidine, a 2 adrenergic agonist, showed some nerve blocking action while other adrenergic agonists showed similar poor degree of nerve blockade. This data suggest that non-effectiveness of epinephrine in blocking nerve conduction is not from the antagonism between adrenergic receptors.

Keyword

Pharmacology, adrenergic receptor agonists, clonidine, epinephrine, isoproterenol, phenylephrine; Physiology, nerve conduction, compound action potential; Rat, sciatic nerve

MeSH Terms

Action Potentials
Adrenergic Agonists
Adult
Animals
Clonidine
Epinephrine
Humans
Isoproterenol
Lidocaine
Male
Nerve Block
Neural Conduction*
Phenylephrine
Rats*
Rats, Sprague-Dawley
Receptors, Adrenergic*
Sciatic Nerve*
Adrenergic Agonists
Clonidine
Epinephrine
Isoproterenol
Lidocaine
Phenylephrine
Receptors, Adrenergic