[Assessment of tissue and intracellular pH following cold-induced vasogenic brain edema--in vitro and in vivo study].

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 intensities 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 influence 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.