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GENERAL ARTICLES

The Relaxant Effect of Propofol on Guinea Pig Tracheal Muscle Is Independent of Airway Epithelial Function and ß-Adrenoceptor Activity

Department of Anesthesiology, University of Hirosaki School of Medicine, Hirosaki, Japan

Address correspondence and reprint requests to Eiji Hashiba, MD, Department of Anesthesiology, University of Hirosaki School of Medicine, 5 Zaifucho, Hirosaki, 036-8562, Japan.

Airway epithelium and vascular endothelium modulate the tension of the underlying smooth muscle by releasing relaxing factors such as prostanoids and nitric oxide (NO). We investigated whether the relaxant effect of propofol on airway smooth muscle is dependent on airway epithelial function. Tracheal spirals of female guinea pigs were mounted in water-jacketed organ baths filled with Krebs-bicarbonate buffer aerated with 95% O₂ and 5% CO₂ at 37°C. Changes in isometric tension of the specimens were measured with a force-displacement transducer and recorded with a polygraph. Propofol (10^-4 to 10^-3 M) inhibited carbachol (CCh)-, histamine (HA)-, or endothelin-1–induced contractions of the muscles in a dose-dependent manner. Neither mechanical removal of the epithelial layer, chemical inhibition of epithelial synthesis of prostanoids, nor NO affected the relaxant effect of propofol on CCh- or HA-induced tracheal contraction. Furthermore, the blockade of ß-adrenoceptors did not change the relaxant effect of propofol. These results indicate that the relaxant effect of propofol on the airway smooth muscle is independent of the epithelial function or ß-adrenoceptor activity. Propofol is an excellent anesthetic for patients with hyperreactive airways in which the epithelial layer is damaged.

Implications: Airway epithelium, as well as vascular endothelium, plays an important role in modulating the baseline tone and reactivity of underlying smooth muscle. We investigated, in vitro, whether the relaxant effect of propofol on airway smooth muscle is dependent on airway epithelial function. We suggest that propofol relaxes airway smooth muscle independently of the epithelial function.

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