Inhibition of rat brain monoamine oxidase type A by 2-aminotetralin and tetrahydroisoquinoline analogues of dopamine.

The in vitro inhibition of rat brain monoamine oxidase type A (MAO-A) by various dopamine analogues is reported and compared to some established inhibitors of the enzyme. The estimated IC50's were found to be in the range 10(-5)-10(-3) mol/l. This makes these compounds more than 10 000 times less potent than the selective MAO-A inhibitor harmaline and more than 10 times less potent than the selective MAO-B inhibitors pargyline and deprenyl. When the brain concentrations that are reached after peripheral administration of these drugs are taken into account it is unlikely that inhibition of MAO is relevant to their effects as has been suggested. Also the endogenous brain concentrations of some tetrahydroisoquinolines are probably too low to produce an inhibition of the enzyme.