Brief periods of skeletal muscle ischemia (ischemic pre-conditioning) alter cellular metabolism in a way that confers protection over subsequent ischemic episodes. The mechanisms behind this effect have been studied indirectly through assays for the byproducts of ATP synthesis and in vitro studies of cellular signaling cascades and ROS generation. There have been no direct, in vivo assessments of the changes in respiration during reperfusion. We employed phosphorescence quenching microscopy in conjunction with a flow-arrest technique to assess the influences of external, pressure-induced 1- to 10-min focal ischemia on interstitial oxygenation (PISFO2) and the consumption of oxygen (VO2) in spinotrapezius muscles of Sprague-Dawley rats. During reperfusion following an ischemic period VO2 was measured by the rate of PISFO2 decline during brief, serial flow-arrest compressions. Our tests of this intermittent compression technique indicate that 5 s of flow-arrest followed by 15 s of flow restoration allow measurement of VO2 without compromising baseline or reperfusion recovery of PISFO2. There was a steady rise in VO2 during early reperfusion which was correlated with increasing ischemic durations. Treatment with cyanide confirmed that at least some of this increase was due to an upregulation of cytochrome c oxidase activity. Nitric oxide (NO) suppressed VO2 during rest and reperfusion, while L-NAME did not influence respiration under normoxic conditions. L-NAME produced a significant rise in VO2 under hypoxic conditions following 10 minutes of ischemia, indicating a greater role of NO in the regulation of respiration during low PISFO2 conditions. We conclude that physiological levels of NO regulate mitochondrial respiration during hypoxia and confirm that pharmacological elevation of [NO] reduces VO2 in a manner consistent with the ischemic pre-conditioning effect.
| Identifer | oai:union.ndltd.org:vcu.edu/oai:scholarscompass.vcu.edu:etd-3236 |
| Date | 09 August 2010 |
| Creators | Nugent, William |
| Publisher | VCU Scholars Compass |
| Source Sets | Virginia Commonwealth University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Theses and Dissertations |
| Rights | © The Author |
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