Abstract 2053: Cardiac Arrest and Resuscitation Increases Nos3-Dependent Formation of Circulating Nitrosylhemoglobin (HbNO)
OBJECTIVE: To characterize the enzyme-mediated nitrosylhemoglobin production following cardiac arrest.
METHODS: Adult female wildtype (WT, n=5) and NOS3−/− (n=8) mice were anesthetized, intubated, ventilated, and instrumented with intravascular catheters. Arrest was induced with intravenous KCl. After 8 minutes of untreated arrest, chest compression and ventilations were performed. Hemodynamics were monitored for up to 120 minutes following return of spontaneous circulation (ROSC). Electron paramagnetic resonance spectroscopy was used to measure nitrosylhemoglobin (HbNO) in whole blood samples obtained from animals (WT and NOS3−/−, n=4 per time point) sacrificed at: baseline (BL), following 8 (CA8) or 20 (CA20) minutes of untreated arrest and at 60 (R60) or 120 (R120) minutes following ROSC. Heart tissue total-NOS3 and phospho-NOS3 were assayed by Western blot.
RESULTS: At BL, NOS3−/−animals displayed higher maximum left-ventricular pressure (LVPmax) than WT animals (113.3 ± 13.19 mmHg vs. 86.8 ± 4.48 mmHg, p<0.05). In the R120 group, ROSC was achieved in 4 of 5 (80%) WT and 4 of 8 (50%) NOS3−/− animals. Following ROSC, NOS3−/−animals displayed lower LVPmax (51.97 ± 7.429 vs. 66.95 ± 4.394 mmHg, p<0.05) and left ventricular stroke work (132.5 ± 26.28 mmHg·μL vs. 456.5 ± 128.9 mmHg·μL, p<0.05) than WT. NOS3−/− animals displayed significantly higher left-ventricular relaxation time constants (tau = 25.82 ± 6.471 ms vs. 15.45 ± 2.223 ms, p<0.05) at R120. At BL, whole blood HbNO concentrations were similar in WT and NOS3−/− animals (0.75 ± 0.10 μM vs. 0.86 ± 0.11 μM, p=0.46). In WT animals, HbNO concentrations increased during untreated arrest at CA20 (1.42 ± 0.19 μM, p<0.05) and following resuscitation at R120 (1.66 ± 0.25 μM, p<0.05) relative to BL. HbNO concentrations were lower in NOS3−/− animals as compared to WT at all time points following cardiac arrest (p< 0.05). Heart tissue from WT animals displayed increased levels of heart tissue total-NOS3 and phospho-NOS3 at R60.
CONCLUSIONS: Circulating HbNO increases following cardiac arrest and resuscitation. Such increases appear to be NOS3-dependent and are associated with improved cardiovascular function.