Displacement of in vivo binding of [3H]brofaromine to rat intestinal monoamine oxidase A by orally administered tyramine.

The reversibility of the interaction of inhibitors with monoamine oxidase (MAO) is thought to provide a safety valve with respect to tyramine potentiation. We sought experimental evidence for this concept by studying the binding of orally administered [3H]brofaromine to the A-form of MAO in the rat ileum. Specific binding, defined by pretreatment with 10 mg/kg clorgyline p.o., amounted to 70-90% of total binding between 30 min and 6 h after administration of the radioligand. Brofaromine and clorgyline dose dependently displaced [3H]brofaromine with ED50 values of about 0.2 mg/kg when administered orally after the radioligand; so did orally administered tyramine in doses relevant for tyramine potentiation in the rat. It was also found that tyramine was relatively more effective in partially MAO-inhibited rats. The data suggest that the concept of reversibility functioning as a safety valve with respect to the potentially hazardous effects of tyramine ingestion is realistic.