Ammonia formation in brain. 1. Studies on slices and suspensions

Abstract

Slices of rat or guinea-pig brain in a glucose-free medium form ammonia at a fairly steady rate for at least 5 hours, during which time a final concentration of 3-4 umoles/100 mg tissue is reached. The concentration of amide N does not change significantly during the aerobic or anaerobic incubation of brain slices, but NH3 formation in glucose-free medium is inhibited under anaerobic conditions and by agents that interfere with electron transport or oxidative phosphoryla-tion. The non-protein nitrogen (NPN) and, to a lesser extent, the acid-soluble phosphorus of brain slices increase significantly during 5 hours incubation, particularly in a glucose-free medium. A small, but probably significant, decrease occurs in the lipid phosphorus fraction and a relatively larger decrease in the ribonucleic acid phosphorus fraction of brain slices in glucose-free medium. In glucose-saline the changes are smaller and not significant. The deoxyribonucleic acid P remains unchanged in the absence as well as in the presence of glucose. The initial NH3 concentration is higher and the final concentration lower when brain suspensions rather than brain slices are incubated. In a hypotonic medium very little NH3 is formed upon incubation, while in isotonic medium some NH3 is formed aerobically, but none anaerobically. The addition of high-energy phosphate groups or of DPN has no effect on NH3 formation. No increase of non-protein nitrogen was found in brain suspensions. Effect of potential parent compounds on the ammonia formation of washed or dialysed brain suspensions and of brain mitochondria was studied, but added nothing to the understanding of the mechanism of NH3 formation. It is concluded that none of the 5 known deaminating brain enzymes is a major factor in the NH3 formation of brain slices and it is suggested that the NH3 arises in a reaction intimately linked with proteolysis.