Levels of p-tyramine in rat brain after chronic administration of MAO-inhibiting antidepressants.

Groups of male Sprague-Dawley rats were injected acutely or chronically with tranylcypromine (10 mg/kg i.p.) or phenelzine (15 mg/kg i.p.) and extracts of their brains were analyzed by electron-capture gas chromatography for concentrations of p-tyramine. Concentrations of p-tyramine were significantly higher than control levels at all time intervals with both drugs, but these increases showed different patterns with each drug. With tranylcypromine treatment, para-tyramine levels peaked at day 2; with phenelzine treatment they increased steadily over the time course, surpassing levels obtained in tranylcypromine experiments by day 8.