局所脳虚血急性期の脳組織内oxypurineの経時的変動

EARLY CHANGES OF OXYPURINES IN RAT BRAIN FOLLOWING FOCAL CEREBRAL ISCHEMIA

　抄録　ラットの左側中大脳動脈を閉塞して局所脳虚血を作製し，手術後4時間までの脳組織中のoxypu-rine （ヒポキサンチン，キサンチン，尿酸）の濃度を経時的に測定した。ラットの屠殺にはマイクロウェーブを用いた。大脳を摘出後左右半球に分割し，過塩素酸とホモジナイズしたのち遠心分離，その上清を濾過して試料とした。測定には高速液体クロマトグラフィを用い尿酸は電気化学検出器，ヒポキサンチン・キサンチンには多波長紫外分光光度計で定量した。その結果ヒポキサンチンは60分で146.2±8.9nmol／g （平均値±標準誤差）とピークとなり，キサンチンは120分で61.5±5.6nmol／gと最高値を示した。尿酸は4時間では19.53±2.42nmol／gと増加していたが，ピークを示さず上昇傾向が続いていた。この結果より虚血脳組織においてプリン代謝の最終段階のヒポキサンチンから尿酸の反応が起きていると考えられ，脳内のプリン代謝の最終産物は今まで言われてきたようなヒポキサンチン・キサンチンではなく，尿酸であると考えられる。

Cerebral hypoxanthine, xanthine, and uric acid levels were measured by high-performance liquid chromatography (HPLC) for up to 4 hours fol-lowing focal cerebral ischemia in the rat. Fifty male Sprague-Dawley rats were subjected to oc-clusion of the left middle cerebral artery under halothane inhalation anesthesia. The animals were sacrificed with microwave at 30, 60, 120, and 240 minutes after surgery. The brains were removed and devided into right and left hemisphere.

Each hemisphere was homogenized with perch-rolic acid and centrifuged. The supernates were filtrated with membrain filter. An aliquot of the filtrate was used for measurement of uric acid, xanthine, and hypoxanthine in both of the ische-mic and contralateral hemisphere by a HPLC system. A HPLC with multiple ultraviolet spec-troscopy was used for measuring hypoxanthine and xanthine. Identification of hypoxanthine and xanthine was made by parallel chromatography of standards, disappearance with xanthine oxidase, and the spectrum of UV absorption. Uric acid was measured by reversed-phase HPLC with el-ectrochemical detection as reported previously.

Hypoxanthine increased rapidly and arrived at a peak value at 60 minutes. Xanthine increased not so rapidly as hypoxanthine and showed the highest value at 120 minutes. Uric acid also increased significantly but very slowly and did not seem to reach the peak value during the observation period. Hypoxanthine is oxidized to xanthine and then xanthine is oxidized to uric acid at the terminal stage of purine degradation. The order of peak times of cerebral hypoxan-thine, xanthine, and uric acid levels following cere-bral ischemia corresponds to the order in purine metabolism. This result strongly suggests that hypoxanthine is degraded into uric acid in ische-mic rat brain. Contrary to the previous reportswhich suggest that the end-product of purine metabolism in mammalian brain is hypoxanthine, we conclude that uric acid is the end-productin the rat brain.