[Selective inhibition by pyrazidol of monoamine oxidase type A in different human and animal tissues]

Pyrazidol (2,3,3a,4,5,6-Hexahydro-8-methyl-1-H-pyrazino (3,2,1-j,k) carbazol hydrochloride) blocked selectively the type A monoamine oxidase (MAO) in mitochondria of different human and animal tissues, irrespective of substrate specificity of the type A MAO in the tissues studied. Thus, in tissues containing both types of MAO (rat, bovine and human brain, rat liver and intestine tissues) pyrazidol inhibited selectively the deamination of serotonin and did not affect the deamination of 2-phenylethylamine--the main substrates in these tissues of the type A and the type B MAO, respectively. In human placenta and rat heart containing only the type A MAO, which catalyzes deamination of 2-phenylethylamine, pyrazidol also inhibited the deamination of serotonin, tyramine and 2-phenylethylamine at comparatively low concentrations and in equal degree. Pyrazidol did not affect significantly the type B MAO in bovune liver and kidney tissues, although the latter enzyme catalyzed deamination of serotonin. The degree of inhibition by pyrazidal of dopamine deamination in various tissues depended on the particular type of MAO mainly involved in oxidation of the amine.