Effects of intravenous anesthetics on the contraction and response of rat trachea to phosphatidylinositol.

Some intravenous anaesthetics have significant effects on the tonicity of airway smooth muscle. There are evidences for a direct relationship between airway smooth muscle contraction and phosphatidylinositol (PI) response. The aims of this study were to clarify 1) the effects of anaesthetics on the cholinergically induced contraction, and 2) the relationship between the effects on the PI response and the contraction. Rat tracheal rings or slices were incubated in Krebs-Henseleit solution containing 5.5 microM carbachol (CCh) in the presence of varying doses of anaesthetics. Thiamylal, fentanyl, ketamine and midazolam all attenuated the CCh-induced contraction. On the other hand, thiamylal augmented inositol monophosphate (IP1) accumulation, whilst ketamine, midazolam and morphine did not have the effect, and fentanyl significantly attenuated IP1 accumulation. These data suggest that airway smooth muscle can be relaxed by intravenous anaesthetics, and that the relaxing effects are not always dependent on the PI system.