Background and Purpose - Recent studies have suggested that autoregulation of cerebral blood flow (CBF) is impaired after traumatic and ischemic brain injury. Given that the levels of superoxide anion (O2.-) are increased in these conditions, we postulate that O2.- contributes to the impairment of CBF autoregulation. Methods - CBF was monitored with laser Doppler flowmetry during increases in blood pressure. Results - During the control period, CBF was well autoregulated after the increase in mean arterial pressure (MAP) from 98±3 to 140±6 mm Hg. The autoregulation index (AI; ΔCBF/ΔMAP) averaged 0.25±0.02 (n=6). O2.- in the brain was then increased by subdural perfusion of xanthine/xanthine oxidase (different concentrations) and catalase. Low concentrations of O2.- decreased basal CBF by 10±1.6% but had no effect on autoregulation (AI, 0.19±0.02; n=6). Higher concentrations of O2.- (0.2 mmol/L xanthine and either 3 or 20 mU xanthine oxidase) increased basal CBF by 30±2% and 42±4%, respectively, and impaired autoregulation of CBF (AI, 0.55±0.03 and 0.76±0.02; n=6). Inclusion of superoxide dismutase in the O2.--generating system restored autoregulation (AI, 0.28±0.05; n=6). Neither inhibition of NO synthase nor the addition of deferioxamine had any effect on the ability of higher concentrations of O 2.- to impair autoregulation of CBF (AI, 0.65±0.07 and 0.72±0.05 respectively; n=6). O2.- also increased the activity of KCa channels in cerebral vascular smooth muscle cells (VSMCs; n=8). Conclusion - These results suggest that O 2.- increases basal CBF and impairs autoregulation of CBF, likely through the activation of KCa channels in cerebral VSMCs.
|Number of pages||6|
|Publication status||Published - Dec 2005|
All Science Journal Classification (ASJC) codes
- Clinical Neurology
- Cardiology and Cardiovascular Medicine
- Advanced and Specialised Nursing