Intestinal metabolism of tyramine by both forms of monoamine oxidase in the rat |
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Authors: | Margherita Strolin Benedetti Thierry Boucher Arvid Carlsson Christopher J Fowler |
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Institution: | 1. Centre de Recherche Delalae, 10 rue des Carrières, F-92500 Rueil-Malmaison, France;3. Department of Pharmacology, University of Göteborg, S-400 33 Göteborg, Sweden |
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Abstract: | The two forms of monoamine oxidase (MAO) in rat intestine and brain homogenates were found to have different Km and Vmax values towards tyramine. The Km values for the A-form of the enzyme towards this substrate were around 120 μM in both cases, whereas the values for the B-form were about 240 μM. As a consequence, the ratio of activities (MAO-A: MAO-B) towards tyramine are dependent upon the substrate concentration. The MAO-A-selective inhibitors, toloxatone and cimoxatone, were found to be competitive inhibitors of the oxidation of tyramine by the A-form of this enzyme in the rat intestine, with Ki values of 3.4 μM and 3.7 nM respectively. The significance of these results in relation to the “cheese effect”, a pressor response to tyramine after monoamine oxidase inhibition, are discussed. |
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Keywords: | Correspondence to Dr M Strolin Benedetti |
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