[Inhibition of monoamine oxidase A and B in the heart and brain of the rat with amitriptyline, pargyline and pirlindol].

The inhibition of monoamine oxidase (MAO) A and B by amitriptyline, pargyline and pirlindole was measured in heart and brain homogenates of rats with tryptamine and beta-phenylethylamine as substrates. The tricyclic antidepressant amitriptyline inhibited MAO B stronger in the brain (Ki = 8.41 X 10(-6) mol/l) as well as in the heart (Ki = 7.03 X 10(-5) mol/l) compared to the A-form (1.51 X 10(-4) and 1.03 X 10(-4) mol/l, respectively). Pargyline diminished the activity of both enzyme forms of the heart in the same range (4.29 and 1.60 X 10(-6) mol/l), whereas in the brain the B-form was blocked in a more pronounced manner, too (5.80 X 10(-8) and 4.01 X 10(-6) mol/l, respectively). In contrast to amitriptyline and pargyline pirlindole inhibited the MAO with tryptamine as a substrate in the brain 100 times (2.49 X 10(-7) mol/l) and in the heart nearly 1000 times (3.42 X 10(-8) mol/l) more than with phenylethylamine as a substrate (5.21 and 5.99 X 10(-5) mol/l, respectively). These results show that amitriptyline and pargyline are relatively selective inhibitors of MAO B, whereas pirlindole blocks the A-form of MAO much stronger than MAO B.