SMOOTH-MUSCLE RELAXANT EFFECTS OF PROPOFOL AND KETAMINE IN ISOLATED GUINEA-PIG TRACHEA

The effects of anesthetics on airway smooth muscle tone are important in the management of patients with asthma. In the present study we eva luated the effect of propofol and ketamine on isolated guinea-pig trac heal preparations mounted for recording isometric contractile force. I n a concentration-dependent way both drugs produced 100% relaxation ir respective of whether tracheal tone was spontaneous or induced by carb achol, histamine, prostaglandin F2alpha 30 mM K+ or 124 mM K+. The rel axant potency of propofol was dependent of the formulation of the drug used. Propofol showed an about 3 times higher potency when solubilize d with hydroxypropyl-beta-cyclodextrin compared with an oil-in-water e mulsion of the drug (Diprivan). Propofol had the greatest potency on t racheal preparations with spontaneous tone (EC50 = 4.0 +/- 0.9 muM). K etamine preferentially relaxed contractions elicited by carbachol (EC5 0 = 120.8 +/- 5.2 muM) and had a lower potency than propofol when tone was spontaneous or induced by other tracheal spasmogens. Since propof ol was a more effective tracheal relaxant in vitro than ketamine, the possibility that propofol, like ketamine, may inhibit bronchoconstrict ion during anesthesia should be studied further.