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Airway epithelium modulate the tone of the airway smooth muscle by releasing epithelium derived relaxing factor or nitric oxide(NO). Ketamine has a direct relaxant effect on airway smooth muscle with the usual clinical doses. We evaluated whether the relaxant effect of ketamine depend on the epithelium and NO in the rat airway. Isolated rat tracheal preparations mounted in water-jacketed organ baths filled with modified Tris Tyrode buffer solution with 100% oxygen at 37oC for recording isometric contractile force. In the first step, Tracheae, in the absence and in the presence of epithelium, were contracted with acetylcholine (10 8 M~10 3 M), and we plotted concentration-response curve for the Ach. And then we examined the inhibitory effect of ketamine(10 5 M, and 10 4 M) on the concentration-response curve for Ach. In the second steps, we studied the effect of N-omega-nitro L-arginine methylester (L-NAME) on the relaxant activity of ketamine(10 6~10 3 M) on trachea contracted by 10 5 M Ach. In the result, 1) Removal of the tracheal epithelium did not change the response to Ach. 2) 10 5 M ketamine not significantly changed, but 10 4 M ketamine shifted to the right the concentration-response curves for Ach in both intact and denuded epithelium rings. Moreover, there was no differdmce in the reactivity of ketamine between intact epithelium rings and denuded epithelium rings. 3) L-NAME did not influence the relaxant effect of ketamine on trachea contracted by 10 5 M Ach. Thus these results indicate that keatmine-induced tracheal smooth muscle relaxation is not dependent on epithelium or epithelium-derived relaxing factor, NO.
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