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Local Anesthetic Inhibitory Action Against Monoamine Oxidase May Play a Role in Spinal Anesthesia
  1. James E. Heavner, DVM, PhD*,
  2. Ralph Gertsch, MD and
  3. Per H. Rosenberg, MD, PhD
  1. From the Department of Anesthesiology and Physiology, Texas Tech University Health Sciences Center, Lubbock, Texas
  2. * Associate Professor and Director of Research.
  3. Research Assistant.
  4. Associate Professor of Anesthesiology.


The comparison of the monoamine oxidase (MAO) inhibitory potency of some commonly used local anesthetics, the examination of their selectivity for two forms of MAO (MAO-A and MAO-B), and the determination of the form of MAO present in the spinal cord of dogs were performed in a study. Hearts from adult Sprague-Dawley rats were used as a source of MAO-A, and hearts from aduit Swiss Webster mice were used as a source of MAO-B. Lumbosacral spinal cords were obtained from dogs anesthetized with halothane. MAO activity in tissue homogenates were measured fluorometrically. The effects of tetracaine, bupivacaine, lidocaine, and mepivacaine on kynuramine oxidation in rat and mouse homogenates were tested. Also tested were the effects of bupivacaine, tetracaine, and lidocaine on spinal cord MAO activity and the effects of clorgyline and pargyline, selective MAO-A and MAO-B inhibitors, respectively. Tetracaine was by far the most potent inhibitor of both types of MAO; the IC50 was 0.3 μM (90 ng/ml) for MAO-A and 5.2 μM (1.56 μg/ml) for MAO-B. All amide local anesthetics caused a 50% inhibition (IC50) of MAO-A and MAO-B at about 1000 times higher concentrations. Tetracaine, lidocaine, and mepivacaine were more potent inhibitors of MAO-A than of MAO-B, whereas bupivacaine and etidocaine exhibited some preference for MAO-B. Spinal cord MAO was identified as type B and was very sensitive to inhibition by tetracaine (IC50 = 4.3 μM; 1.29 μg/ml). Bupivacaine and lidocaine were weaker inhibitors, with a 30% inhibition produced by the highest concentrations tested (2 mM (648 μg/ml) bupivacaine and 10 mM (2.7 mg/ml) lidocaine). Results of this study support the hypothesis that tetracaine and perhaps other ester-linked local anesthetics may produce analgesia by affecting the turnover of monoamines associated with the endogenous pain control system via inhibition of spinal cord MAO.

  • Anesthetics
  • local
  • Heart
  • monoamine oxidase
  • Monoamine oxidase
  • inhibitors
  • Spinal cord
  • monoamine oxidase
  • Tetracaine

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