In the current study, we investigated links between O2-regulated H2O2formation and the hypoxic induction of mRNA for tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine synthesis, in O2-sensitive PC-12 cells. During exposure of PC-12 cells to 5% O2, H2O2concentration decreased by 40% as measured with 2',7'-dichlorofluorescein (DCF). Treatment with H2O2reduced TH mRNA during nor...