Inhalation of Volatile Anesthetics Depresses Contraction of Canine Tracheal Smooth Muscle Induced by Vagal Stimulation or Acetylcholine in vivo

Abstract

The inhibition of inhalational anesthetics to tracheal smooth muscle contraction induced by vagal stimulation was studied in vivo. Twelve adult beagle dogs were anesthetized with pentobarbital and vecuronium, and mechanically ventilated. The isometric contraction force of opened tracheal smooth muscle was measured by an electric transducer. The contraction was induced by the electrical vagal stimulation (20 Hz, 30 V, 2 msec, n=12) or the arterial infusion of acetylcholine (0.1μg/kg, n=6) during inhalation of halothane, isoflurane and sevoflurane (0.75 and 1.5 minimum alveolar concentration : MAC). The tension of tracheal muscle increased to 150〜160 % without inhalation of anesthetics. However, the increases were significantly inhibited to 115 ± 5%, 127 ± 7% and 119 ± 7 % during inhalation of halothane, isoflurane and sevoflurane (1.5 MAC, p<0.05), respectively. Isoflurane revealed weaker inhibition than halothane during vagal stimulation (p<0.05). All the anesthetics (1.5MAC) significantly depressed the tracheal contraction induced by acetylcholine infusion (p<0.05), in which there was no difference among the three anesthetics. In conclusion, sevoflurane has equally potent inhibitory effect as halothane against tracheal contraction induced by the vagal stimulation or the acetylcholine infusion.