Effects of local anesthetics on monoamine oxidase, and their membrane effects.

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Abstract
The effects of various local anesthetics on rat brain and liver monoamine oxidase (MAO) and their antihemolytic and local anesthetic effects were studied. All local anesthetics tested at 1 .RTM. 10-7 to -1 .times. 10-3 M inhibited MAO activity in rat liver mitochondria with 5-hydroxytryptamine (5-HT) as substrate. The order of potency was tetracaine > procaine > dibucaine > lidocaine > prilocaine. Tetracaine and procaine inhibited 5-HT oxidation much more than .beta.-phenethylamine (PEA) oxidation. Dibucaine inhibited PEA oxidation as much as 5-HT oxidation. MAO inhibition by local anesthetics other than dibucaine was reversible. Tetracaine and procaine inhibited 5-HT oxidation competitively, whereas dibucaine inhibited it noncompetitively. Antihemolytic effects were observed with dibucaine and tetracaine at concentrations of 6 .times. 10-5 and 1 .times. 10-4 M, respectively. The order of surface anesthetic potencies was dibucaine > tetracaine > prilocaine > lidocaine > procaine. Evidently, the inhibition of MAO activities by local anesthetics depends on both electrostatic and hydrophobic interactions between these drugs and enzyme-associated phospholipids or the hydrophobic regions of proteins.

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