Conduction block by clonidine is not mediated by alpha2-adrenergic receptors in rat sciatic nerve fibers.
Reg Anesth Pain Med
; 25(6): 620-5, 2000.
Article
em En
| MEDLINE
| ID: mdl-11097671
ABSTRACT
BACKGROUND AND OBJECTIVES:
Clonidine, an alpha(2)-adrenergic agonist, has been shown to prolong local anesthesia. It appears that clonidine by itself produces conduction block by acting on peripheral nerves. However, whether clonidine-induced conduction block is mediated through alpha(2)-adrenergic receptors remains unclear. The purpose of this study was to see if clonidine's nerve-blocking action was through alpha(2)-adrenergic receptors by examining clonidine's action in the presence of alpha(2)-adrenergic antagonists.METHODS:
The compound action potentials (CAPs) evoked by electrical stimuli were recorded from the isolated rat sciatic nerve in a recording chamber. Conduction block was examined by analyzing CAPs with regard to peak amplitude and time-to-peak in the presence of clonidine alone or clonidine plus alpha(2)-adrenergic antagonist yohimbine or idazoxan.RESULTS:
Both clonidine and yohimbine produced concentration-dependent, reversible, conduction block. Based on concentration-response relationships, the 50% of effective concentration (EC(50)) were estimated to be 1.61 +/- 0.51 mmol/L (mean +/- SD) for clonidine and 51.4 +/- 27.2 micromol/L for yohimbine. A mixture of equal volumes of 2.07 mmol/L clonidine and 55.6 micromol/L yohimbine produced conduction block to a level close to the mean value between conduction blocks induced by 2.07 mmol/L clonidine alone and 55.6 micromol/L yohimbine alone. Addition of idazoxan, a more specific alpha(2)-adrenergic antagonist than yohimbine, to clonidine was without effect on clonidine-induced conduction block.CONCLUSIONS:
The results indicated that the mixture of clonidine and yohimbine, in which either drug inhibited impulse conduction, produced conduction block in an additive manner, and that clonidine-induced conduction block was not reversed by coapplication with a specific alpha(2)-adrenergic antagonist idazoxan. These data suggest that clonidine's effects likely depend on mechanisms not mediated by alpha(2)-adrenergic receptors.
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Base de dados:
MEDLINE
Assunto principal:
Nervo Isquiático
/
Clonidina
/
Receptores Adrenérgicos alfa 2
/
Agonistas alfa-Adrenérgicos
/
Condução Nervosa
Limite:
Animals
Idioma:
En
Revista:
Reg Anesth Pain Med
Assunto da revista:
ANESTESIOLOGIA
/
NEUROLOGIA
/
PSICOFISIOLOGIA
Ano de publicação:
2000
Tipo de documento:
Article