Xanthine oxidase activation by IH contributes to increased ROS levels.

<p><b>A.</b> Effect of IH on XO activity. XO activity was determined in PC12 cells exposed to increasing cycles of intermittent hypoxia (IH_10,30,60) and after re-oxygenation following exposure to IH₆₀<b>. B–C.</b> Effect of allopurinol (ALLO), a XO inhibitor and silencing of XO by siRNA on XO activity in cells exposed to IH. <b>D.</b> Acontiase activity levels were monitored as an index of ROS generation in cells exposed to normoxia (N) or IH with and without ALLO (20 µM) treatment. *<i>p</i><0.05; n.s. not significant, <i>p</i>>0.05.