Effects of propofol on guinea pig respiratory smooth muscle

The effects of propofol on the tone of guinea pig respiratory smooth muscle was studied both in vitro and in vivo. In vitro, the activity of propofol on tracheal smooth muscle was investigated using a force displacement transducer for isometric tension responses. Isoproterenol was used as the control. Concentration-response curves to propofol and isoproterenol were obtained using a cumulative dose schedule. Propofol (0.32-10.24 μg·ml^-1) relaxed the tracheal smooth muscle in a concentration-dependent manner, but was less potent than isoproterenol (equipotent molar ratio 29 000∶1). This effect of propofol was not affected by prior administration of atropine, propranolol, prazocin, or yohimbine, and it did not appear to be mediated via calcium antagonism. The solvent for propofol (10% intralipid) had no effect on the tracheal smooth muscle in vitro. The in vivo study measured the effect of propofol on lung pressure in deeply anesthetized guinea pigs using histamine induced bronchoconstriction. Propofol (1-4.5 mg·kg^-1, i.v.) exhibited neither relaxant nor constrictor effects. It is possible that the effects of propofol observed in vitro are due to nonspecific action, while the finding of no effect in vivo could be due to different tissue sensitivity to propofol, i.e., tracheal smooth muscle may be more responsive than bronchial smooth muscle. Propofol does not seem to have any deleterious effects on airway smooth muscle.