Effects of halothane and isoflurane on antigen- and leukotriene-D4-induced constriction of guinea pig trachea.

We investigated the mechanism of the action of volatile anesthetics on the airway smooth muscle constricted by an antigen and leukotriene-D4 (LTD4). Excised tracheal rings from ovalbumin-sensitized guinea pigs were suspended in eight tissue baths. Halothane or isoflurane was aerated into four tissue baths, while the remaining four served as time controls. To assess the antispasmogenic activity of halothane and isoflurane, concentration-response curves for antigen and LTD, were constructed exposed to anesthetics and compared to controls. The spasmolytic activity of halothane and isoflurane was measured in the tracheal rings constricted by a single antigen challenge or by EC50 of LTD. Both halothane and isoflurane produced significant rightward shifts of ovalbumin and LTD, concentration-response curve with corresponding increases in the EC50 values. Halothane increased the EC50 value for LTD, from 5.38 +/- 0.43 x 10-9 M to 1.2 +/- 0.18 x 10-8 M, and for ovalbumin from 1.2 +/- 0.06 x 10-4 mg/ml to 3.03 +/- 0.28 x 10-4 mg/ml. Isoflurane increased the EC50 value for LTD, from 5.17 +/- 0.64 x 10-9 M to 8.98 +/- 1.01 x 10-9 M, and for ovalbumin from 1.21 +/- 0.09 x 10-4 mg/ml to 2.61 +/- 0.19 x 10-4 mg/ml. Furthermore, halothane and isoflurane significantly reduced the magnitude of the antigen-and LTD4-induced constriction. In 30 min intervals, 1% and 2% halothane reduced the magnitude of the ovalbumin-induced constriction by 32% and 50%, respectively, while isoflurane (2% and 4%) caused relaxation of 16% and 35%, respectively. The magnitude of LTD4-induced constriction was reduced by 17% and 24%, with 1% and 2% halothane, respectively. Isoflurane (2% and 4%) reduced this constriction by 25% and 25% respectively. In conclusion, halothane and isoflurane attenuate and prevent the constrictive response of airway smooth muscle to allergen and LTD. A direct, nonspecific dilating effect is suggested as the mechanism responsible for the observed effects.