EFFECTS OF INTRAVENOUS ANESTHETICS ON NORMAL AND PASSIVELY SENSITIZEDHUMAN ISOLATED AIRWAY SMOOTH-MUSCLE

Background General anesthetics may modify airway responsiveness. The a uthors investigated the effect of thiopental, propofol, and etomidate on airway smooth muscle. Methods: Contraction experiments were done in human airway rings that were either normal or passively sensitized wi th asthmatic serum. The effect of propofol and etomidate was also stud ied on both [Ca2+](i) increase measured by microspectrofluorimetry in isolated myocytes and isometric contraction in the rat trachea Results : In human bronchi thiopental (10(-7) to 10(-4) M) induced a concentra tion-dependent contraction. Neither propofol nor etomidate altered bas eline tone, but both anesthetics reduced histamine-induced contraction . In human immunologically sensitized isolated bronchi, propofol (3 x 10(-4) M) reduced histamine reactivity (Delta F-max in %) to a greater degree than in nonsensitized tissues (64.4 +/- 15.7% and 16.4 +/- 8.5 %, respectively; n = 6, P < 0.05), whereas the effect of etomidate (10 (-4) M) was similar in both types of tissue (24.1 +/- 6% and 22.3 +/- 15%, respectively, n = 6). In rat isolated tracheal myocytes, propofol (3 x 10(-4) M) and etomidate (10(-4) M) altered the [Ca2+](i) signal i n response to the depolarizing agent potassium chloride and the muscar inic agonist acetylcholine. Accordingly, the two anesthetics also redu ced the mechanical response of rat tracheal rings to these agonists. C onclusions: whereas thiopental contracts human isolated bronchi, propo fol and etomidate reduce histamine-induced contraction in human isolat ed ah-way smooth muscle that were either not sensitized or passively s ensitized with asthmatic serum. This effect involves inhibition of bot h electro-and pharmacomechanical coupling.