Distribution, Metabolism, and Disappearance of Intraventricularly Injected p-Tyramine in the Rat

Abstract

The major cerebral metabolic products of intraventricularly injected p-tyramine were octopamine and p-hydroxyphenylacetaldehyde. Only tiny amounts of p-hydroxyphenylacetic acid and p-hydroxyphenylethanol were found and these were located in the cerebral cortex (i.e. 'rest'). In brain regions isolated in the absence of pargyline the principal metabolite was p-hydroxyphenylacetaldehyde recovered in an acidic–neutral fraction; in the presence of pargyline, however, the majority of the label was associated with the amines tyramine and octopamine. In the caudate nucleus octopamine was essentially absent both in the presence and absence of pargyline.The loss of octopamine from all regions in the presence of pargyline was approximately exponential (i.e. first order) whereas in the absence of the monoamine oxidase inhibitor the loss was more complicated than first order. In most cases the loss of p-tyramine was greater than first order. Approximate half-lives based on these clearance values indicated a rapid turnover for p-tyramine and octopamine in all regions both in the presence and absence of pargyline.