Abstract 3029: Major Impact of Genetic and Physiologic Variables on Ischemia/reperfusion Injury in the Murine Heart
The mouse has become the most commonly used model for assessing the response of the heart to ischemic injury. However, the confounding influences of genetic strain, gender, age, body temperature, and blood pH on infarct size after coronary artery occlusion (O) and reperfusion (R) in the non-preconditioned (naïve) or preconditioned murine heart are unclear and often overlooked, potentially causing artifacts. Thus, we studied 754 mice from 19 different strains (among others, ICR, 129Sv, C57BL/6, C3H, BALB/c, FVB/N, B6/129, B6/CBA) and distributed them into 64 different groups depending on strain and (i) ischemic preconditioning (PC) protocol, (ii) coronary O time, (iii) gender, (iv) age, (v) core body temperature, and (vii) blood pH. Mice underwent O either without (naïve) or with prior PC consisting of six 4-min O/4-min R cycles 10 min (early PC, EPC) or 24 h (late PC, LPC) prior to 30 – 45-min O and 24 h R. In the naïve state, only FVB/N mice had infarct size significantly smaller than other strains (17.9±2.4% of region at risk; P<0.05). All strains except FVB/N benefited from the cardioprotection afforded by the early phase of PC, whereas LPC was not uniformly preserved among strains. Gender had a major impact:
it affected susceptibility to ischemic injury in naïve ICR mice (infarct size: 51.7±2.2% vs. 39.7±3.9% of region at risk in male and female, respectively; P<0.05);
it determined whether LPC developed in ICR mice; and
it affected the degree of protection afforded by EPC in 129Sv mice. Mild hypothermia (36.0 °C) and respiratory acidosis (pH=7.2) resulted in significant cardioprotection in ICR mice (69.3% and 45.8% reduction in infarct size, respectively[P<0.05]); this is the first report that ventilatory parameters (which usually are arbitrarily selected) affect infarct size. In conclusion, the susceptibility of the murine heart to ischemic injury and PC is importantly affected by strain and gender. In addition, even minor deviations in body temperature and blood pH (which are often not even measured) are sufficient to produce statistically significant differences in infarct size, which could be erroneously ascribed to therapeutic effects. These variables need to be carefully considered and quantitated in order to avoid artifactual conclusions.
This research has received full or partial funding support from the American Heart Association, Great Rivers Affiliate (Delaware, Kentucky, Ohio, Pennsylvania & West Virginia).