Cerebral microvascular permeability and CSF pH in anaesthetized rats

The idea that the blood-brain barrier (BBB) may be made slightly permeable by an acid load on the brain side was tested in single pial venular capillaries of anaesthetized young rats. The fluorescent dye, Lucifer Yellow (457 Da), was used as a fluid-phase marker to measure permeability in the presence of a free radical scavenger. Tight microvessels were unresponsive to pH changes of 0.3-0.5 units. Vessels that were permeable showed small, significant increases in permeability with decreasing pH (2.19 +/- 0.562 x 10(-6) cm s-1 (pH unit)-1). This effect increased with increasing permeability.