A modified in vitro method for studying tracheal smooth muscle response to drugs

Background: Vascular or nasal mucosal strips have been successfully used to study smooth muscle contractility in vitro. Using the trachea of the rat, we developed a simple and rapid in vitro technique for testing the effects of drugs that induce tracheal constriction or relaxation. Methods: We used our preparation to test the effectiveness of acetylcholine and methacholine as tracheal contraction drugs and the effectiveness of verapamil as a tracheal relaxing drug. A 5 mm long portion of rat trachea was submersed in 30 ml Kreb's solution in a muscle bath at room temperature. Changes in tracheal contractility in response to the application of parasympathetic mimetic agents were measured using a transducer connected to a Pentium III computer equipped with polygraphy software. Results: Addition of parasympathetic mimetics to the incubation medium caused the tracheal to contract in a dose-dependent manner. Addition of verapamil, a relaxation agent, induced a relaxation response only when the preparation had been pretreated with a tracheal constricting agent such as methacholine. Responses to verapamil were dose-dependent. Conclusion: The degree of drug-induced tracheal contraction or relaxation is dose-dependent. This method could prove useful for studying the effects of drugs on tracheal smooth muscle activity.