[The effect of droperidol and sevoflurane on serotonin-induced bronchoconstriction in dog]

Serotonin is a potent bronchoconstrictor, but the site of bronchoconstriction has not been determined. The present study was performed in dogs to clarify the site of bronchoconstriction induced by serotonin as well as to clarify the bronchodilating effect of droperidol and sevoflurance on the serotonin-induced bronchoconstriction by means of deflation flow-volume curve (DFVC) method, passive expiratory flow volume curve (PEFVC) method and respiratory system impedance measurement by forced oscillation method. Infusion of serotonin (60 micrograms.kg-1.min-1) induced a significant decrease in maximal expiratory flow at 10% of maximal expiratory volume (DEF10) by DFVC method and a significant increase in respiratory system impedance (Z). After droperidol (0.1 mg.kg-1) injection, DEF10 and Z returned to the control level and they remained unchanged even after the termination of serotonin infusion. Respiratory system compliance and resistance by PEFVC were unchanged by both serotonin and droperidol infusion or sevoflurane. Inhalation of 5% sevoflurane during serotonin infusion caused no significant change in DEF10. These findings indicate that serotonin-induced bronchoconstriction involves the small airway as well as the large airway. It is suggested that droperidol reversed serotonin-induced small airway constriction probably due to the antagonism of serotonin receptor in the airway. Bronchodilating effect of sevoflurane is probably limited in the small airway constricted by serotonin.