Abstract

Rabbit liver and spider homogenates showed a decrease in monoamine oxidase activity after iproniazid, and recovery of the enzyme in about 15 days. After 20 days, rabbit liver showed a significant increase in MAO activity over controls. At the time of maximal MAO inhibition, the catabolism of d-amphetamine in the spiders' bodies was slowed down significantly and the effect of d-amphetamine on spiders' webs had increased about tenfold. On the fifth day after iproniazid the d-amphetamine sensitivity of spiders was again close to normal and d-amphetamine catabolism and MAO activity were only slightly slowed down. It is concluded that iproniazid inactivates the system catabolizing d-amphetamine as well as the MAO system.

Imipramine in a single dose showed some effect on MAO activity of rabbit liver or spider homogenate and no effect on d-amphetamine catabolism and sensitivity. Webs were larger when d-amphetamine was given to spiders 5 days after imipramine. Only 3 injections of 100 mg/kg of imipramine brought rabbit liver MAO activity down significantly. There was a significant rebound increase after 10 days. The results indicate that imipramine, unlike iproniazid, has almost no immediate effect on MAO activity. In addition it does not slow down d-amphetamine catabolism and has no detectable d-amphetamine potentiating activity. Web-building of spiders was apparently unchanged after both antidepressant drugs alone.