In vivo Monoamine Oxidase Inhibition Measured by Potentiation of Tryptamine Convulsions in Rats

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Abstract
Evidence was presented in a previous publication (Jour. Pharmacol. and Exptl. Therap. 126 223. 1959.) that potentiation of the con-vulsant action of tryptamine serves as a useful measure of in vivo monoamine oxidase (MAO) inhibitory activity. The present report is concerned with the in vivo MAO inhibitory activity of a variety of pharmacological agents tested by this technique. All drugs were tested orally, unless otherwise specified, at their time of peak activity. Drugs effective as in vivo MAO inhibitors (arranged in descending order of potency) included harmine (subcutaneous), tranylcypromine (SKF trans 385), SKF cis 385, d-[alpha]-methylphenemyl-hydrazine, d,l-[alpha]-methylphen-ethylhydrazine, harmine (oral), d,l-N-acetylmethionylisopropylhy-drazide (RO-4-1018), nialamide, phenelzine, iproniazid, and 1-isonico-tinyl-2-phenylisopropylhydrazine. Compounds which failed to effect significant in vivo MAO inhibition included diphenhydramine, tri-pelennamine, isoniazid, dihydroergotamine, mescaline, procaine, pro-caine amide, [beta]-dimethylaminoethyldiphenylpropylacetate (SKF No. 525-A), and 2-amino-l-(3,4-methylenedioxphenyl) propane hydrochloride (SKF No. 5-A).