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Hydroxyl radical production during myocardial ischemia and reperfusion in cats
C A O'Neill1, L W Fu, B Halliwell
1Department of Internal Medicine, University of California, Davis 95616, USA.
Insights
Reactive oxygen species, specifically hydroxyl radical (HO•), are produced during myocardial ischemia and reperfusion. The duration of ischemia influences HO• production rates during reperfusion in cats.
Area of Science:
- Cardiovascular Physiology
- Biochemistry
- Oxidative Stress Research
Background:
- Reactive oxygen species (ROS) stimulate cardiac sympathetic afferent nerve endings during myocardial ischemia and reperfusion.
- Hydroxyl radical (HO•) is a key ROS implicated in cardiac injury.
Purpose of the Study:
- To investigate the production of HO• during brief myocardial ischemia and reperfusion in a feline model.
- To determine if HO• production during reperfusion is dependent on the duration of preceding ischemia.
Main Methods:
- Feline model of reversible left anterior descending (LAD) coronary artery occlusion (2, 5, and 10 minutes).
- Measurement of tyrosine metabolites (p-, m-, and o-tyrosine) in coronary venous blood as indicators of HO• production.
- Perfusion of ischemic myocardium with phenylalanine to assess HO• production during ischemia.
- Pharmacological inhibition of HO• production using deferoxamine and dimethylthiourea.
Main Results:
- HO• is produced during both ischemia and reperfusion.
- Tyrosine metabolite production rates increased with longer ischemic durations (5 and 10 minutes) during reperfusion compared to 2 minutes.
- The highest rate of tyrosine production was observed immediately post-ischemia, suggesting washout of accumulated HO•-derived products.
- HO• production during ischemia was significant, with tyrosine production rates of 82 ± 11, 6.6 ± 0.4, and 1.7 ± 0.3 nmol·min⁻¹·g⁻¹ for p-, m-, and o-tyrosine, respectively.
- Deferoxamine and dimethylthiourea significantly reduced HO• production during both ischemia and reperfusion.
Conclusions:
- Hydroxyl radical (HO•) is generated during brief myocardial ischemia and reperfusion.
- The duration of myocardial ischemia directly influences the rate of HO• production during the subsequent reperfusion period.
- HO• production immediately after ischemia may result from the washout of products accumulated during the ischemic phase.
Abstract:
We previously showed that generation of reactive oxygen species during myocardial ischemia and reperfusion stimulates cardiac sympathetic afferent nerve endings. We hypothesized that, in this feline model of brief ischemia and reperfusion, HO. is produced during ischemia and the rate and concentration of production of HO.during reperfusion is dependent on the duration of myocardial ischemia. Therefore, we evaluated the time dependency of production of HO. during reperfusion after 2, 5, and 10 min of reversible occlusion of the left anterior descending (LAD) coronary artery to induce ischemia in cats (n = 10). Blood samples collected from the coronary vein at 0.25, 1, 2, and 4 min after 2 min of ischemia revealed net cumulative rate of production of p-, m-, and o-tyrosine of 99 +/- 31, 10 +/- 5.1, and 0.8 +/- 0.2 nmol.min-1.g-1, respectively. After 5 min of ischemia, net cumulative rates of production of p-, m-, and o-tyrosine during reperfusion were 177 +/- 63, 74 +/- 26, and 1.6 +/- 0.8 nmol.min-1.g-1, respectively, whereas after 10 min of ischemia production rates were 153 +/- 42, 78 +/- 29, and 2.1 +/- 0.5 nmol.min-1.g-1, respectively. The highest rate of production of tyrosines was observed immediately after ischemia, perhaps indicating a washout of HO.-derived products that had accumulated in the myocardium during ischemia. To evaluate production of HO. during ischemia, deoxygenated saline (PO2 10 +/- 0.9 mmHg) containing phenylalanine was perfused into the ischemic coronary vascular bed through a cannula placed in the LAD (n = 16). Perfusate was collected from the coronary vein during the 10 min of ischemia. Net production of HO. during ischemia, measured by the production of p-, m-, and o-tyrosine, was 82 +/- 11, 6.6 +/- 0.4, and 1.7 +/- 0.3 nmol.min-1.g-1, respectively. Pretreatment with deferoxamine (10 mg/kg, n = 7) or dimethylthiourea (10 mg/kg, n = 6) decreased net production of HO. during ischemia and reperfusion. These results demonstrate that HO. is produced during brief ischemia and reperfusion, with the greatest amount being produced immediately after ischemia. Additionally, we show that the duration of brief ischemia determines the rate of production of HO. during reperfusion.