ISOFLURANE-MEDIATED AND HALOTHANE-MEDIATED DILATION OF DISTAL BRONCHIIN THE RAT DEPENDS ON THE EPITHELIUM

Background: Respiratory epithelium releases substance(s) that can modu late bronchoconstriction in response to constrictive agonists and enha nce bronchodilation in response to certain bronchodilators. The hypoth esis that the bronchodilatory effect of isoflurane and halothane depen ds on the epithelium was tested in rat distal bronchial segments. Meth ods: Wistar rat bronchial segments of the fourth order (diameter appro ximately 100 mu m) were dissected, After preconstriction with 5-hydrox ytryptamine, each bronchial segment was exposed to increasing concentr ations of 0% to 3% isoflurane or 0% to 3% halothane under four conditi ons: after epithelial rubbing, after pretreatment with the nitric oxid e synthase inhibitor N-G-nitro-L-arginine, after pretreatment with the cyclooxygenase inhibitor indomethacin, or with no preintervention (co ntrol), Changes in bronchial diameter were monitored using an in vitro video detection system. Results: Both isoflurane and halothane produc ed concentration-dependent bronchodilation (P < 0.001 for either anest hetic; 40% +/- 11% [mean +/- SD] dilation for 3% isoflurane and 57% +/ - 10% dilation for 3% halothane), For both anesthetics, bronchodilatio n was significantly but incompletely attenuated by epithelial rubbing (12% +/- 7% dilation for 3% isoflurane [P < 0.01] and 31% +/- 10% dila tion for 3% halothane [P < 0.01]), by pretreatment with indomethacin ( 20% +/- 8% dilation for 3% isoflurane [P < 0.02] and 21% +/- 9% dilati on for 3% halothane [P < 0.001]), or by L-NNA (9% +/- 7% dilation for 3% isoflurane [P < 0.005] and 39% +/- 12% dilation for 3% halothane [P < 0.05]). Epithelial rubbing did not impair nitroprusside-associated bronchodilation. Conclusions: Isoflurane- and halothane-mediated bronc hodilation depends at least partially on the epithelium and may involv e both a prostanoid and nitric oxide Ln distal rat bronchi.