Inhibitory Effects of Ethaverine, a Homologue of Papaverine, on Monoamine Oxidase Activity in Mouse Brain

Abstract

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 showed an inhibition of MAO activity in a concentration-dependent manner (57.6% inhibition at 40 μM). Papaverine also inhibited MAO activity (38.1% inhibition at 40 μM). However, laudanosine and tetrahydropapaverine did not inhibit MAO activity. The IC₅₀ value of ethaverine for MAO was 25.5 μM. Ethaverine non-competitively inhibited MAO activity with a substrate kynuramine. The K_i value for ethaverine was 11.9 μM. In addition, ethaverine proved to preferentially inhibit type B MAO activity in a concentration-dependent manner, with an IC₅₀ value of 32.8 μM. These results suggest that ethaverine partially contributes to the regulation of catecholamine content.