XDH and brain ischemia: However, the distribution of XOR in the brain is quite low,[27] though some in vivo studies found that XOR activity increases during hypoxia and reperfusion.[24, 25] On the other hand, we previously found that XOR expression levels in brain were extremely low compared with those in liver even after reperfusion.[6] These results are consistent with the finding that the effects of XOR inhibitors were limited in brain ischemia.