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Inhibitory effects of the alpha-2 adrenergic agonists clonidine and dexmedetomidine on enhanced airway tone in ovalbumin-sensitized guinea pigs

Published online by Cambridge University Press:  01 January 2008

M. Yamakage*
Affiliation:
Sapporo Medical University School of Medicine, Department of Anesthesiology, Sapporo, Hokkaido, Japan
S. Iwasaki
Affiliation:
Sapporo Medical University School of Medicine, Department of Anesthesiology, Sapporo, Hokkaido, Japan
J.-I. Satoh
Affiliation:
Sapporo Medical University School of Medicine, Department of Anesthesiology, Sapporo, Hokkaido, Japan
A. Namiki
Affiliation:
Sapporo Medical University School of Medicine, Department of Anesthesiology, Sapporo, Hokkaido, Japan
*
Correspondence to: Michiaki Yamakage, Department of Anesthesiology, Sapporo Medical University School of Medicine, South 1, West 16, Chuo-ku, Sapporo, Hokkaido 060-8543, Japan. E-mail: yamakage@sapmed.ac.jp; Tel: +81 11 611 2111, ext. 3568; Fax: +81 11 631 9683
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Summary

Background and objective

The alpha-2 adrenergic agonists clonidine and dexmedetomidine are used as an antihypertensive and a sedative, respectively. The aim of this study was to determine the effects of these agonists on ovalbumin-sensitized airway tone in guinea pigs.

Methods

The animals were divided into two groups: control and sensitized. The sensitized group received ovalbumin intraperitoneally and was boosted by exposure to aerosolized ovalbumin. The effects of the alpha-2 agonists were investigated by measuring (1) total lung resistance and (2) smooth muscle tension using a tracheal ring preparation.

Results

In the control group, acetylcholine significantly increased total lung resistance in a dose-dependent manner. In the sensitized animals, total lung resistance was significantly higher (by 95%) at 6 μg kg−1 acetylcholine than that in the control group. Both clonidine and dexmedetomidine had a slight but significant inhibitory effect on the response curve of lung resistance at higher concentrations of carbachol, a potent muscarinic receptor agonist. Similar to the data obtained in the control group, both clonidine and dexmedetomidine significantly decreased total lung resistance and the inhibitory effects of these alpha-2 agonists on lung resistance were significantly distinguishable. Similar direct inhibitory effects of the alpha-2 agonists on carbachol-induced muscle contraction were observed in both the control and sensitized groups, the inhibitory effects in the sensitized group being significantly greater.

Conclusion

Both clonidine and dexmedetomidine can relax the airway even in the hyper-reactive state.

Type
Original Article
Copyright
Copyright © European Society of Anaesthesiology 2007

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Footnotes

This paper was presented in part at the annual meeting of the American Society of Anesthesiologists, Las Vegas, NV, USA, October 23–27, 2004 and at the annual meeting of the American Society of Anesthesiologists, Atlanta, GA, October 22–26, 2005.

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