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Plasma nitrite concentrations decrease after hyperoxia-induced oxidative stress in healthy humans

Background: We measured plasma nitrite, the biochemical marker of endothelial nitric oxide (•NO) synthesis, before and after hyperoxia, in order to test the hypothesis that hyperoxia-induced vasoconstriction is a consequence of reduced bioavailability of •NO due to elevated oxidative stress. Methods: Ten healthy males breathed 100% normobaric O2 for 30 min between the 15th and 45th min of the 1 h study protocol. Plasma nitrite and malondialdehyde (MDA), arterial stiffness (indicated by augmentation index, AIx) and arterial oxygen (PtcO2) pressure were measured in the 1st, 15th, 45th and 60th minute of the study. Results: Breathing of normobaric 100% oxygen during 30 min caused an increase of PtcO2 (from 75 ± 2 to 412 ± 25 mm Hg), AIx (from −63 ± 4 to −51 ± 3%) and MDA (from 152 ± 13 to 218 ± 15 nmol/L) and a decrease in plasma nitrite (from 918 ± 58 to 773 ± 55 nmol/L). During the 15-min recovery phase the plasma nitrite, AIx and MDA values remained altered. Conclusions: This study suggests that the underlying mechanism of hyperoxia-induced vasoconstriction may result from reduced •NO bioavailability due to elevated and sustained oxidative stress.

nitric oxide; oxygen; vasoconstriction

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