DIFFERENTIAL ACTION OF IPRONIAZID (MARSILID) AND BETA-PHENYLISOPROPYLHYDRAZINE (CATRON) ON ISOLATED ATRIA

¹ University of Florence, Italy
² Department of Materia Medica and Therapeutics, University of Aberdeen, Scotland
³ Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut

Two classes of inhibitors of monoamine oxidase (MAO), represented by iproniazid and phenylisopropylhydrazine (PIH), have been studied for their actions on spontaneously-beating, isolated atria of the guinea pig. Despite certain properties in common, these compounds demonstrated some striking differences in action. Both PIH and iproniazid completely inhibited MAO activity in the atria. Only iproniazid, however, was able to antagonize some of the depressant effects of reserpine and to prevent, in large part, spontaneous depletion of catecholamines from the heart. Iproniazid produced a positive inotropic and chronotropic effect which was relatively slow in developing but long-sustained. This was blocked by dichloroisoproterenol (DCI). PIH, on the other hand, produced an initial positive inotropic and chronotropic effect which was followed by a depression of the atria. The initial excitation could be effectively blocked by DCI, a result which unmasked the depressant phase of the action of PIH. Both PIH and iproniazid were shown to reduce the action of nicotine on the isolated atria; PIH was more potent in this regard, and in high concentrations could completely prevent the action of nicotine.