Several studies have assigned catecholamines a pro-oxidant role and have therefore correlated catecholamines with the development of different pathophysiological processes. This pro-oxidant effect could be due to the Fenton reaction (i.e., Fe(II) + H2O2 Fe(III) + center dot OH + OH-), which is known to be utilized by catecholamines to reduce Fe(III) and O-2. In this work, the ability of a few catecholamines (i.e., dopamine, epinephrine and norepinephrine) to reduce Fe(III) to Fe(II) and O-2 to H2O2 and to produce center dot OH radicals by the Fenton reaction was evaluated at different pH values. The catecholamines were observed to produce Fe(II) and H2O2 at different pH values. Therefore, center dot OH radical production was enhanced at pH values where only Fe(III) reduction was observed. At pH values near 7.0, the catecholamines did not enhance the production of center dot OH radicals. Instead, the catecholamines acted as antioxidants forming bis-complexes, i.e., [Fe(LH)(2)](+). The catecholamines sequestered iron from the reaction system and thereby prevented iron from reacting with other compounds such as H2O2. (C) 2016 Elsevier B.V. All rights reserved.