ラット脳内11—HETEの同定および虚血性脳浮腫との関係

IDENTIFICATION OF 11-HETE IN RAT BRAIN AND ITS RELEVANCY TO ISCHEMIC CEREBRAL EDEMA

　抄録　ラット脳内リポキシゲナーゼ代謝，およびそれと虚血性脳浮腫との関係を，高速液体クロマトグラフィー（HPLC），およびガスクロマトグラフィー・マススペクトロメトリー（GC-MS）を用い検討した。ラット中大脳動脈閉塞後，24時間，72時間で，in situ freezing法により脳を摘出し，そのhomogenateをHPLCおよびGC-MSにかけ，hydroxy-eicosatetraenoic acids （HETEs）の同定定量を行った。又，ラット脳を微小血管（MV）とそれ以外の分画に分け，それぞれに含まれるHETEを測定した。正常および虚血脳中には，11—HETEのみが認められ，特にMVには，他分画の約10倍量含まれていた。対照群（n＝18），虚血24（n＝10），72時間群（n＝18）で，それぞれ1,288±66.3,1,101±48,1,663±147（mean±SE） ng／g wet weightの値を示し，脳浮腫が最大となる虚血後72時間で，有意の増加が認められた（P＜0.05）。以上の結果より，リポキシゲナーゼ代謝が虚血性脳浮腫発現に関与していることが考えられる。又，リポキシゲナーゼ代謝物がMVに主に存在することより，それが，血液脳関門の機能に影響を及ぼしていることが推察される。

Eicosanoids are thought to be important in the pathogenetic mechanism of ischemic brain damage. But little is known about lipoxygenase products and their roles in brain. In the present study, lipoxygenase metabolism in the brain and its rele-vancy to ischemic brain edema were studied using high performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS). The rat middle cerebral artery (MCA) oc-clusion model was used because the time course of ischemic edema formation has been well known.

The rat brain was fixed by in situ freezing 24 and 72 hours after MCA occlusion, and removed. Identification and quantitative analysis of hydroxy-eicosatetraenoic acids (HETEs) in normal and isc-hemic brain homogenates was performed by HPLC and GC-MS. The rat brain was divided into the microvessel (MV) fraction and the rest. Then the same analysis was carried out in the both fractions obtained from the normal rat brain. Only 11- HETE was detected in the normal and ischemic brain. Quantitatively, normal brains contained 1288±66 (mean±SE) of 11-HETE ng/g wet we-ight, while the hemispheres rendered ischemic for 24 and 72 hours after MCA occlusion contain-ed 1101±±48, and 1663±±147, respectively. The 11-HETE content was significantly increased 72 hours after MCA occlusion (p<0.05). The MV fraction of rat brain contained 11-HETE (653 ng/ mg protein) ten times as much as the other frac-tion.

The identifiction of 11-HETE in the rat brain is a new finding. The present study disclosed that 11-HETE was produced mainly in the brain MV and its synthesis was enhanced concomitant with the edema formation. The above results indicate the possibility that the lipoxygenase products affect the blood-brain barrier function and are involved in the evolution of ischemic brain edema.