Distribution and activity of monoamine oxidase in mouse tissues

Abstract

5-Hydroxytryptamine (5-HT) tryptamine, tyramine, [beta]-phenylethylamine,isoamylamine and benzylamine have been tested as substrates of amine oxidase in homogenates of mouse brain, kidney, liver, lung and spleen. Mouse kidney contains a monoamine oxidase which destroys 5-HT more rapidly than tyramine, tryptamine or [beta]-phenylethylamine. This is also true of lung and spleen. 5-HT was oxidized most rapidly by lung. In liver homogenates 5-HT was oxidized less rapidly than any other monoamine tested yet the rate was only slightly less than that observed with lung tissue. isoAmylamine and benzylamine, although oxidized by liver, brain and lung, were not attacked by kidney and spleen. Differences in substrate specificity and relative rates of oxidation of the substrates serve to distinguish the amine oxidase from each tissue. (+)-Amphetamine was 7 times as potent as (-)-amphetamine as an inhibitor of brain amine oxidase; the difference was less with kidney. The guanidine analogue of 5-HT was synthesized. It is a weak inhibitor of monoamine oxidase. These findings are discussed in relation to the function of amine oxidase.