慢性肝不全ラットの大脳皮質におけるグルタミン酸の代謝動態

GLUTAMATE METABOLISM IN CEREBRAL CORTEX OBTAINED FROM CHRONIC HEPATIC FAILURE RATS

　抄録　肝性脳症における脳内アミノ酸代謝異常を解明すべく，脳内に最も高濃度に存在し，また興奮性神経伝達物質でもあるglutamateに注目してその代謝変動の面から検討した。慢性肝不全モデルはWistar系雄ラットに四塩化炭素を投与し作製後，無麻酔下で断頭し，頭頂葉より厚さ0.5mmの100mg切片を得て，酸素で飽和したGey's balanced salt solution 2.5mlにL-（U-¹⁴C） glutamate 0.5μCiを加え37℃で45分間incubateした。この間に産生したCO₂は25％β—phenylethylamineで捕捉し，大脳皮質切片は75％ethanol抽出後に薄層クロマトグラフィーで二次展開を行いアミノ酸を分離してその放射能活性を測定し，以下の結論を得た。慢性肝不全群では①CO₂産生能は有意に増加した（p＜0.001）。②アミノ酸分画ではaspartate,glutamineが増加し（p＜0.001），glutamate,GABAでは不変であった。③全体としてみるとglutamate取り込みは亢進し，慢性肝不全脳におけるglutamateの代謝動態の特性として，アンモニア処理機構としてのglutamine産生促進のみならず，glutamateのTCAサイクルを介する代謝の亢進を認めた。このような代謝の特徴は肝不全時にglutamateがその炭素骨格をTCAサイクルに移し，エネルギー産生維持に積極的に関与していることを反映すると考えられた。

The present investigation was carried out in order to elucidate the amino acid metabolism in hepatic failure with particular emphasis placed on glutamate. For this purpose, chronic hepatic failure models were produced in adult male Wistar rats by succesive carbontetrachloride injection (0.20ml/100g. B.W., twice/week) for 13 weeks. They were confirmed to develop chemical changes compartible with hepatic failure, showing markedly elevated serum levels of NH₃, GOT and ALP. Animals were killed by decapitation during fasting and the brains were removed immediately. After the pa-rietal cortical slices were incubated for 45 min at 37℃ together with L-(U-¹⁴C) glutamate in O₂-saturated Gey's balanced salt solution, they were homogenized in 75% ethanol and deproteinized with water saturated chloroform. The radio-activities of liberated CO₂, glutamate and its meta-bolites (glutamine, aspartate and GABA) obtained from the slices were measured.

The amount of radioactivity recovered from CO₂, glutamine and aspartate revealed a significant increase (p<0.001), while that of glutamate and GABA remained unchanged. The main source of the CO₂ is believed to originate from TCA cycle rather than the decarboxylation of glutamate to form GABA, and glutamate forms glutamine when it fixes ammonia. Furthermore, glutamate is con-verted into aspartate via TCA cycle when the carbon was labeled. Therefore, the results indi-cate that in chronic hepatic failure brains gluta-mate metabolism is enhanced through TCA cycle as well as ammonia fixation mechanism.