British Journal of Anaesthesia, 2001, Vol. 86, No. 2 249-253
© 2001 The Board of Management and Trustees of the British Journal of Anaesthesia
Comparison of relaxant effects of propofol on methacholine-induced bronchoconstriction in dogs with and without vagotomy
Department of Anesthesiology, University of Hirosaki School of Medicine, Hirosaki 036-8562, Japan*Corresponding author
Propofol has been suggested to have in vivo airway relaxant effects, although the mechanism is still unclear. In this study, we determined whether propofol could antagonize methacholine-induced bronchoconstriction and determined whether vagotomy modifies this relaxant effect. Fourteen mongrel dogs anaesthetized with pentobarbital and pancuronium were assigned to a control group (n=7) and a vagotomy group (n=7). The trachea was intubated with a special endotracheal tube that had a second lumen for insertion of the bronchoscope. Bronchial cross-sectional area, which was monitored continuously through the bronchoscope, was measured with image analysis software. Bronchoconstriction was elicited with methacholine (0.5 µg kg–1 + 5.0 µg kg–1 min–1) until the end of the experiment. Thirty minutes after the start of methacholine infusion, propofol 0, 0.2, 2.0 and 20 mg kg–1 was administered. Changes in bronchial cross-sectional area were expressed as percentages of the basal area. Plasma concentrations of propofol and catecholamine were measured by high-performance liquid chromatography. Maximal inhibition (bronchoconstriction = 0%, baseline = 100%) and IC50 (concentration producing 50% inhibition of maximal effect) produced by propofol was obtained from each concentration–response curve using a curve-fitting program. Methacholine decreased bronchial cross-sectional area to 49.3% (95% confidence interval 38.5–60.1%) and 45.3% (34.8–55.7%) of the baseline value. Propofol 20 mg kg–1 significantly reversed this effect: bronchial cross-sectional area was reduced to 77.8% (66.2–89.6%) and 75.9% (64.0–87.9) in the control and vagotomy groups respectively. The two groups did not differ significantly in the maximal inhibitory effect of propofol [control group, 61.1% (46.3–75.9%), vagotomy group, 64.2% (40.1–88.3%)] or pIC50 [control group 5.03 (4.55–5.51), vagotomy group 4.86 (4.49–5.24)]. Therefore, the relaxant effects of propofol on methacholine-induced bronchoconstriction may not be mediated centrally. Propofol may relax airway smooth muscles directly or through the peripheral vagal pathway.
Br J Anaesth 2001; 86: 249–53
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