Glutamic acid metabolism in perfused cat brain studied with 14C-labelled glutamic acid.

The rate of transport of blood glutamic acid into the brain and the rate of metabolic conversion of the amino acid in the brain were derived by the use of the brain perfution method in vivo and in situ with [D.HC] ·Lglutamic acid. The net uptake of glutamic acid by the brain was observed. Most of the radioactivity released from the brain into the cerebral venous blood was found to consist of glutamine. Small but significant amounts of output as radioactive GSH and CO2 were also found. Glutamic acid transport and its rate of metabolism were lowered in the glucose. free condition. The size of the compartment of the small glutamic acid pool, which was related closely to the blood glutamic acid, and that of the large glutamic acid pool, which was related closely to the blood glucose, were calculated and compared with each other. ∗PMID: 4249890 [PubMed indexed for MEDLINE] Copyright c ©OKAYAMA UNIVERSITY MEDICAL SCHOOL Acta Merl. Okayama 24, 333-342 (1970) GLUTAMIC ACID METABOLISM IN PERFUSED CAT BRAIN STUDIED WITH HC-LABELLED GLUTAMIC ACID Shosuke WATANABE, Saburo OTSUKI, Yoshio NAKASHIMA, Kazuyasu EDAMATSU and Katsusuke MITSUNOBU Department of Neuro-Psychiatry, Okayama University Medical School, Okayama, Japan (Director: Prof. S. Otsuki) Received for publication, April 26, 1970 Following the intravenous or intracisternal administration of glutamic acid, the rapid exchange of the amino acid between blood and brain and the compartmentation of glutamic acid metabolism in brain have already been shown (LAJTHA, BERL and WAELSCH 1959, BERL, LAJTHA and WAELSCH, 1961). These findings led to the present study on the quantitative aspect of the fate of blood glutamic acid after entering the brain and upon its subsequent metabolism in the brain. Utilizing the brain perfusion method, [U.JC] .L-glutamic acid was added to the perfusion blood and kept at a constant specific activity throughout the experiments. The rate of incorporation of radioactIvity into free glutamate, aspartate and glutamine of the brain was measured. And also, the amount of radioactive glutamine, GSH and respiratory CO2 released into the cerebral venous blood was measured. The brain perfusion experiments were performed with the blood containing either glucose in the normal concentration or no glucose, so that the effect of hypoglycemia on the glutamic acid metabolism of the brain could be studied. MATERIALS AND METHODS Young adult cats were used for the experiments. Details of the technique of perfusion of the brain in vil'O and is situ have already been described (GEIGER and MAGNES 1947, OKUMURA, IKEDA and WATANABE 1962). The roller type pump was used for the artificial brain perfusion. The blood once perfused through the brain was discarded with the exception of the venous blood samples for analysis. Continuous records of the electroencephalogram (EEG) and cerebral blood flow (measured with electromagnetic flow meter) were taken during the experiments. In each experiment about 5 fJ.C of radioactive L-glutamic acid and 500 I~moles of unlabelled-L-glutamic acid were added to 1000 ml of perfusion blood. The perfusion blood consisted of washed bovine red blood cells suspended in a Krebs-Ringer solution containing 6 per cent dextran (average molecular weight 40,000) and 0.2 per cent bovine serum albumin. For the standard perfusion, the