Short- and long-term effects of L-DOPA treatment upon monoamine oxidase: A comparative study in several rat tissues

Abstract

The influence of L-DOPA administration (250 mg/kg/day) to the rat for up to 26 days, upon the oxidative deamination of 5-hydroxytryptamine, dopamine and benzylamine, has been investigated in homogenates from heart (atria and ventricles separately), aorta, brain, liver and kidneys. In the cardiovascular tissues and the kidneys, the metabolism of these amines was generally increased after L-DOPA treatment, although these changes were only maintained over the time course of the experiment in kidney homogenates. In contrast, relatively few changes were obtained in brain and liver. At least three enzyme activities, called MAO-A, MAO-B and a clorgyline-resistant amine oxidase, have previously been identified as being responsible in varying degrees for the metabolism of these substrates in the different tissues studied. The present results are discussed in the context of possible selective influences of L-DOPA upin these activities. Similar considerations have been applied to various developmental changes in amine metabolism, observed in some tissues of growing control animals during the course of these experiments. The results reveal a considerable variation among different rat tissues in the ability of L-DOPA administration to modify amine metabolism. This variation is dependent upon the particular deaminating enzyme studied, and the period of L-DOPA administration.