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Biphasic modulation of vascular nitric oxide catabolism by oxygen
Xiaoping Liu1, Crystal Cheng, Nicholas Zorko
1Davis Heart and Lung Research Institute, The Ohio State Univ., 473 W. 12th Ave., Columbus, OH 43210, USA. Liu-11@medctr.osu.edu
Summary
Vascular wall nitric oxide (NO) catabolism is regulated by oxygen levels. Reduced NO breakdown at low oxygen maintains blood vessel tone, while anaerobic conditions accelerate NO removal.
Area of Science:
- Cardiovascular Physiology
- Biochemistry
- Vascular Biology
Background:
- Endothelium-derived nitric oxide (NO) is crucial for regulating vascular tone.
- Reduced NO bioavailability contributes to cardiovascular diseases.
- Mechanisms controlling NO catabolism in the vascular wall under varying oxygen conditions remain unclear.
Purpose of the Study:
- To investigate the regulation of NO catabolism in the vascular wall under normoxic, hypoxic, and anaerobic conditions.
- To determine the role of oxygen concentration and specific enzymes in NO breakdown.
Main Methods:
- Isolated rat aorta studies measuring NO and O2 consumption using electrochemical sensors.
- Experiments under varying oxygen tensions (normoxic, hypoxic, anaerobic).
- Inhibition studies using specific enzyme inhibitors (NaCN, deferoxamine, diphenylene iodonium) and superoxide dismutase.
Main Results:
- Aortic NO consumption was enhanced under normoxic conditions.
- NO consumption decreased with decreasing oxygen levels (hypoxic conditions).
- A paradoxical increase in NO consumption occurred under anaerobic conditions, inhibited by NaCN and reproduced by purified cytochrome c oxidase (CcO).
Conclusions:
- Cytochrome c oxidase (CcO) is implicated in vascular NO catabolism.
- Reduced NO catabolism at low oxygen tensions helps maintain vascular tone.
- Accelerated anaerobic NO catabolism may clear excess NO in ischemic tissues.