Stress reduces in vivo inhibition of monoamine oxidase by phenelzine in rat brain.

The level of inhibition of rat whole brain monoamine oxidase activity produced by the irreversible monoamine oxidase inhibitor phenelzine has been studied with or without concurrent cold restraint stress. We have found that phenelzine caused significantly less enzyme inhibition when given during a period of stress than during a control period. Thus, stress can reduce the in vivo potency of MAO inhibitors. This would be compatible with an increased production of the reversible, endogenous monoamine oxidase inhibitor, tribulin, competing for the active site of the enzyme.