REGIONAL METABOLISM OF MET-ENKEPHALIN AND CHOLECYSTOKININ ON INTACT RAT-BRAIN SLICES - CHARACTERIZATION OF SPECIFIC PEPTIDASES

The metabolism of Met-enkephalin and cholecystokinin (CCK) 8-(sulfated ) by intact microslices was studied in rat brain regions. incubation o f brain slices with Met-enkephalin (400 mu M) resulted in a linear rat e of disappearance of parent peptide and appearance of metabolic fragm ents whose rate of accumulation was specific to brain region. The degr adative rate (pmol/min/mg of protein) of Met-enkephalin was high in ca udate-putamen (5,160 +/- 120) and lower in nucleus accumbens (3,630 +/ - 110)and frontal cortex (3,180 +/- 120). Inhibition of aminopeptidase s decreased Met-enkephalin degradation 150-97% vs. control) in frontal cortex but was less effective in caudate-putamen (20-34%). Tyr-Gly-Gl y and Phe-Met were recovered in caudate-putamen and nucleus accumbens, whereas negligible quantities of these fragments were recovered from frontal cortex, Phosphoramidon, an inhibitor of neutral endopeptidase 24.11, decreased Met-enkephalin degradation in caudate-putamen (14%) b ut had no effect on that in frontal cortex. A cocktail of bestatin or leuhistin (inhibitors of aminopeptidases), phosphoramidon, and captopr il (an inhibitor of angiotensin converting enzyme) protected Met-enkep halin from degradation (recovery >95%) in caudate-putamen, CCK 8-(sulf ated) degradation on slices from caudate-putamen, nucleus accumbens, a nd frontal cortex was not altered by inhibitors of neutral endopeptida se 24.11, metalloendopeptidase 24.15, angiotensin converting enzyme, o r thiol proteases, Inhibitors of either aminopeptidases or serine prot eases produced small reductions (13-30%) in CCK degradation in each re gion. These data provide evidence for regional and structural specific ity in terminating the actions of neuropeptides.