Original ArticleEffects of Bupivacaine on the Isolated Rat Tracheal Smooth Muscle
Introduction
Vascular or nasal mucosal strips have been used to study smooth muscle contractility in vitro.1, 2 Effects of drugs on the airway have been examined using a rat tracheal smooth muscle preparation because this tissue has a resting tone and pharmacological responses similar to those of the human airway. We developed a simple and rapid test for identifying agents that affect tracheal smooth muscle directly.3 The development of such a test could help resolve the inconsistencies observed in trachea responses to drugs in vivo.
Bupivacaine is an amide-linked local anesthetic that is usually used for infiltration, nerve block, epidural and intrathecal anesthesia. Bupivacaine acts by binding to the sodium channels and blocking sodium influx into nerve cells, which prevents depolarization of the nerve fibers. Some reports have shown that aerosol inhalation of local anesthetics can reduce cough, inflation and deflation reflexes, and facilitate tracheal intubation during surgical operations.4, 5, 6 Intravenous administration of lidocaine or bupivacaine has been reported to attenuate bronchial hyper-reactivity in awake humans.7 It has been demonstrated that bupivacaine or lidocaine applied topically to the smooth muscle of isolated rat tail arteries can inhibit vascular contraction in response to adrenergic activation.8 The effect of bupivacaine topically applied to the trachea has not been well explored. In the present study, we used a simple in vitro technique to investigate the direct effects of bupivacaine on the contractile response of isolated rat tracheal smooth muscle to methacholine and electric field stimulation (EFS).
Section snippets
Study design
This study was approved by the Animal Experiment Review Board (IACUC-08-146). All chemical reagents were obtained from Sigma (St Louis, MO, USA) and were of the highest purity available. Adult rats were anesthetized using intraperitoneal pentobarbital administration (45 mg/kg) and two pieces of trachea each ∼5 mm long were removed from each rat. Each specimen was mounted using two steel plates and immersed in a bath containing 30 mL of Krebs solution (118 mM NaCl, 4.7 mM KCl, 2.5 mM CaCl2,
Results
The degree of contraction or relaxation in tracheal strips was determined from the tension applied to the transducer. The addition of bupivacaine to the bath did not significantly alter the resting tension in non-stimulated tracheal strips (Figure 1).
Tracheal contraction induced by methacholine was easily detected and the tissue remained in a contracted state until the drug was rinsed from the tissue. When bupivacaine was cumulatively applied to the steady state of 10−6 M methacholine-induced
Discussion
Many in vitro assays have been used for investigating tracheal responses to local anesthetics or other drugs. In those assays, the tracheal preparation was opened by cutting through the cartilage rings or the tracheal mucosa was removed or only tracheal smooth muscle strips were used.9, 10, 11, 12, 13 All of these procedures violate the normal physiology in vivo. The tracheal strips used in our examination were excised as an intact trachea ring without damaging the mucosa or smooth muscle;
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Effects of dexmedetomidine on the isolated rat tracheal smooth muscle
2013, Journal of Experimental and Clinical Medicine(Taiwan)Citation Excerpt :A passive tension of 0.3 g was applied to the strips, and subsequent changes in tension were recorded continuously using Chart V4.2 software (PowerLab; ADInstruments, Colorado Springs, Colorado, USA). A previous study showed that methacholine can induce a dose-dependent contraction of a tracheal strip, and that a concentration of 10−6 M can result in a significant contraction.10,11 Our preliminary test results showed that a tracheal strip immersed in the bath solution used for subsequent experiments did not contract when basal tension was applied.
Effects of levobupivacaine on isolated rat tracheal smooth muscle
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