Inhibitory effects of ethaverine, a homologue of papaverine, on monoamine oxidase activity in mouse brain

The effects of benzylisoquinoline compounds such as ethaverine, laudanosine , and tetrahydropapaverine on monoamine oxidase (MAO, EC 1.4.3.4) activity in mouse brain were investigated, Ethaverine show ed an inhibition of MAO a ctivity in a concentration-dependent manner (57.6% inhibition at 40 muM). P apaverine also inhibited MAO activity (38.1% inhibition at 40 muM). However , laudanosine and tetrahydropapaverine did not inhibit MAO activity. The IC 50 value of ethaverine for MAO was 25.5 muM. Ethaverine non-competitively i nhibited MAO activity with a substrate kynuramine. The K-i value for ethave rine was 11.9 muM. In addition, ethaverine proved to preferentially inhibit type B MAO activity in a concentration-dependent manner, with an IC50 valu e of 32.8 muM. These results suggest that ethaverine partially contributes to the regulation of catecholamine content.