Effect of aromatic amino acids, pentylenetetrazole and yohimbine on isatin and tribulin activity in rat brain.

The effects of i.p. injection of 3 aromatic amino acids and two anxiogenic agents on rat brain isatin concentration and tribulin (endogenous monoamine oxidase inhibitor) activity were investigated. Isatin levels were significantly increased by pentylenetetrazole, confirming the link with 'anxiety', but were unaffected by the other compounds. In contrast, tribulin activity was significantly increased by phenylalanine and tryptophan as well as by both pentylenetetrazole and yohimbine. Whilst these findings shed no light on the mode of synthesis of isatin, they clearly demonstrate the existence of rat brain monoamine oxidase inhibitory activity that is different from it.