Exercise-induced brachial artery vasodilation: role of free radicals

Originally thought of as simply damaging or toxic accidents of in vivo chemistry, free radicals are becoming increasingly recognized as redox signaling molecules implicit in cellular homeostasis. Indeed, at the vascular level, it is plausible that oxidative stress plays a regulatory role in normal vascular function. Using electron paramagnetic resonance ( EPR) spectroscopy, we sought to document the ability of an oral antioxidant cocktail ( vitamins C, E, and alpha- lipoic acid) to reduce circulating free radicals, and we employed Doppler ultrasound to examine the consequence of an antioxidant- mediated reduction in oxidative stress on exercise- induced vasodilation. A total of 25 young ( 18 - 31 yr) healthy male subjects partook in these studies. EPR spectroscopy revealed a reduction in circulating free radicals following antioxidant administration at rest ( similar to 98%) and as a consequence of exercise ( similar to 85%). Plasma total antioxidant capacity and vitamin C both increased following the ingestion of the antioxidant cocktail, whereas vitamin E levels were not influenced by the ingestion of the antioxidants. Brachial artery vasodilation during submaximal forearm handgrip exercise was greater with the placebo ( 7.4 +/- 1.8%) than with the antioxidant cocktail ( 2.3 +/- 0.7%). These data document the efficacy of an oral antioxidant cocktail in reducing free radicals and suggest that, in a healthy state, the aggressive disruption of the delicate balance between pro- and antioxidant forces can negatively impact vascular function. These findings implicate an exercise- induced reliance upon pro- oxidant- stimulated vasodilation, thereby revealing an important and positive vascular role for free radicals.