[Changes in the brain GABA system after repeated injections of pyridoxal-5'-phosphate and its Schiff base with GABA]

A state of the gamma-aminobutyric acid (GABA) system (glutamate, glutamate decarboxylase, GABA, GABA-alpha-ketoglutarate aminotransferase) and the coupled reactions (alpha-ketoglutarate dehydrogenase complex, aspartate- and alanine aminotransferases) was studied in three brain structures (cerebellum, brain cortex and truncus cerebri) after multiple administration of pyridoxal-5'-phosphate (PALP) and its Shiff base with GABA (5 injections at doses 10.0 and 15.0 mg/kg of body mass, respectively). Non-coenzymatic effects of PALP were found to prevail within 1 hr after its last administration: inhibition of PALP-dependent aminotransferases and activation of the alpha-keto-glutarate oxidative decarboxylation were observed. The opposite effects were detected after addition of PALP to brain homogenates in vitro. Administration of the PALP-GABA complex exhibited qualitatively similar to those of PALP effects on the reactions studied in brain. The data obtained suggest that parenteral administration of the coenzyme preparation caused a number of metabolic effects, which are sometimes far from unambigously predicted theoretical considerations. The similarity of PALP and PALP-GABA effects appears to demonstrate ready biotransformation of the Shiff base with liberation of PALP and GABA.