Aminopeptidase activity is asymmetrically distributed in selected zones of rat brain. 
Levels of soluble aminopeptidase (AP), measured as arylamidase activity using L-Leucine-2-Naphthylamide (Leu-2-NA) as substrate, were determined in the soluble fraction of eleven zones of rat brain.  Results showed that AP activity is asymmetrically distributed in frontal cortex and hypothalamus with both left sides having significantly higher levels of AP activity, respectively, than the right sides.  Simultaneously, the activities of lactate dehydrogenase (LDH) and glutamate-oxalacetate aminotransferase (GOT) were measured in the same cerebral regions; no significant difference was recorded in these activities between either side of the rat brain in any of the zones studied.  Provided that aminopeptidases are involved in the degradation of some endogenously released neuropeptides, the results suggest a new mode of expression of cerebral lateralization.