Vasogenic edemaにおける組織および細胞内pHの評価—In vitroおよびin vivoによる実験的検索

ASSESSMENT OF TISSUE AND INTRACELLULAR PH FOLLOWING COLD-INDUCED VASOGENIC BRAIN EDEMA:IN VITRO AND IN VIVO STUDY

　抄録　脳組織の酸塩基平衡は脳組織の機能と密接に関係しており，以前より微小電極や生物化学的手法にて測定されてきたが，これらでは局所評価が困難である。このため我々はpH指示薬であるumbelliferone（UBF）を組織化学的手法にて用い，本法の定量化につき検討すると共に，脳凍結損傷モデルでの浮腫部位の組織pHの測定を行った。UBF濃度別pH用紙と含水量別pH既知の凍結標本を用い370nmと340nmの紫外線励起後450nmの螢光を写真撮影し各々の螢光強度差よりnomogramを作製した。UBFの螢光強度はpHと高い相関を示したが，含水量の影響も受けていた。脳凍結損傷による組織化学法では浮腫部の白質pHは軽度alkalosisを呈していた。このalkalosisは主として血漿（pH≒7.4）の細胞外漏出を反映していると考えられた。一方病巣周辺の皮質ではほぼ中性を示したが，in vivoのUBF動脈内投与ではacidosisであった。この差異は後者が細胞内pH （pH_i）を，前者が組織pH （pH_t）を反映しているためと考えられた。UBF法はpH_tおよびpH_iの測定が可能であり，組織化学法は局所的差異を知るのに有用であるが，定量化には含水量の影響に留意が必要である。

Acid-base balance is closely related to the brain function and various methods have been applied to estimate the intracellular, extracellular or tissue pH.

Umbelliferone, a fluorescent pH indicator, has been used to study either intracellular or tissue pH. In the present study, umbelliferone was used for histochemically estimating the tissue pH in the rat brain. The pH nomograms were made from the difference between fluorescent in-tensities at 450 nm on both excitations at 370 nm and 340 nm at different tissue water contents and different umbelliferone concentrations. Linear correlations were noted under each condition but 0.125% w/v umbelliferone provided the best estimation of tissue pH because of the least in-fluence of water contents.

Using this concentration of umbelliferone, a histochemical study was done to estimate the sequential changes in tissue pH following cold-induced vasogenic brain edema in rats. The results revealed a clear delineation of brain edema and the mild alkalosis in the edematous tissue, which probably reflects the pH of leaked plasma fluid. While the pH in the cortex around the lesion was neutral in the histochemical study, it was acidic in the in vivo study. This discrepancy is probably due to the former indicating the tissue pH while the latter the intracellular pH.

Thus, the alkalosis in the edema fluid and the intracellular acidosis in the cortex around the lesion were noted in the cold-induced vasogenic edema.