Effects of levobupivacaine on isolated rat tracheal smooth muscle

Levobupivacaine has been developed as a safer alternative to bupivacaine because of its reduced systemic toxicity. However, the effect of directly delivering levobupivacaine into tracheal smooth muscle has not been adequately explored. We performed this study to determine the in vitro effects of levobupivacaine on isolated rat tracheal smooth muscle. A portion of rat trachea 5 mm in length was mounted in 30 ml of Krebs solution in a muscle bath at 37 °C. The following effects of levobupivacaine were assessed: (1) the effect on tracheal smooth muscle resting tension (n = 6), (2) the effect on contraction caused by 10⁻⁶ M methacholine (n = 6) and (3) the effect on electrically induced tracheal smooth muscle contractions (n = 6). Levobupivacaine caused dose-dependent relaxation in the trachealis muscle precontracted with 10⁻⁶ M methacholine. Contraction inhibition was statistically significant when 10⁻⁵ and 10⁻⁴ M levobupivacaine were applied, compared with the contraction inhibition that occurred in the control groups (p < 0.01). A high dose of levobupivacaine also decreased the spike contraction induced by electrical field stimulation. This study indicated that high concentrations of levobupivacaine might antagonize the cholinergic receptors and inhibit parasympathetic function of the trachea.