Abstract 17446: Intra-arrest Hypothermia Protection Requires Endothelial Nitric Oxide Synthase

Abstract

Introduction: Intra-arrest hypothermia (IH), cooling the body to 30 - 32°C during cardiac arrest, has previously been shown as protective in a mouse model of cardiac arrest. Hypothermia has also been shown to protect cultured cardiomyocytes exposed to simulated ischemia/reperfusion (I/R) in a nitric oxide synthase-dependent manner. However, the effect of IH on NOS signaling in whole animal models of cardiac arrest has not been studied. We hypothesized that mice deficient in endothelial NOS (NOS3) would not be protected by IH following cardiac arrest. Furthermore, we hypothesized that IH would alter NOS3 signaling in WT mouse hearts. METHODS: Adult NOS3 -/- (B6.129P2-Nos3tm1Unc/J, n = 30) and WT (C57Bl/6J, n = 24) mice underwent 8 min of cardiac arrest. At 6 min, mice were randomized to normothermia (NT, 37°C) or IH (30°C) followed by re-warming to 37°C at 60 min post-ROSC. Animals were hemodynamically monitored for 2 h and then neurologically scored at regular intervals up to 48 h. In separated experiments, cardiac NOS3 signaling was evaluated in similarly randomized mice at the end of the arrest period. RESULTS: In NOS3-/- mice, IH and NT groups had similar 48 h neurologically-intact survival rates (20 % vs. 0%, p=0.80). By contrast survival rates were significantly higher in IH vs. NT treated WT mice (47% vs. 0%, p=0.03). After 8 min of arrest heart p-NOS3(Ser1177) was significantly lower in NT relative to sham controls (p<0.05) and IH treated WT mice (p<0.05). Also during arrest, phosphorylation of the metabolically-sensitive AMP activated protein kinase p-AMPK(Thr172) was similarly increased (p<0.05) following arrest in both IH and NT groups. Cardiac p-Akt(Ser474/Thr308) content was unchanged at 8 min of arrest (p>0.05) in both groups. CONCLUSIONS: Loss of NOS3 abrogates IH protection following cardiac arrest. Maintenance of cardiac NOS3 phosphorylation during cardiac arrest may play an important role in determining survival in this model. Such maintenance of phosphorylation appears to be independent of upstream kinase phosphorylation.