Effect of iproniazid on metabolism of noradrenaline in man

¹ Memorial Research Center and Hospital, The University of Tennessee, Knoxville, Tennessee

Adult males were infused with dl-noradrenaline-2-C¹⁴ and the radioactive urinary catabolites were analyzed. At the end of 24 hr, 78% of the infused dose was recovered. The recovered urinary radioactivity was distributed as follows: noradrenaline, 5%; 3-O-methylnoradrenaline, 5%; 3-O-methylnoradrenaline sulfate, 19%; 3-methoxy-4-hydroxymandelic acid, 36%. The remaining radioactivity was distributed among other catabolites, known and unknown; these catabolites have been described. After treatment with iproniazid, the distribution of the urinary radioactivity between the two major catabolites, 3-O-methylnoradrenaline sulfate and 3-methoxy-4-hydroxymandelic acid, was significantly altered. For the 24-hr period, 3-O-methylnoradrenaline sulfate was greatly increased and accounted for 46% of the total radioactivity recovered; conversely, 3-methoxy-4-hydroxymandelic acid was greatly decreased and accounted for only 10% of the total radioactivity recovered. Significant increases were also noted for noradrenaline and 3-O-methylnoradrenaline during the first 6 hr. These results demonstrate that iproniazid alters the metabolism of noradrenaline by inhibiting the action of monoamine oxidase. The neutral and acidic catabolites have been described. Vanillic acid has been identified as a metabolite of noradrenaline.