Systematic evaluation of a novel model for cardiac ischemic preconditioning in mice

Cardioprotection by ischemic preconditioning (IP) remains an area of intense investigation. To further elucidate its molecular basis, the use of transgenic mice seems critical. Due to technical difficulty associated with performing cardiac IP in mice, we developed an in situ model for cardiac IP using a hanging-weight system for coronary artery occlusion. This technique has the major advantage of eliminating the necessity of intermittently occluding the coronary artery with a knotted suture. To systematically evaluate this model, we first demonstrated correlation of ischemia times (10-60 min) with infarct sizes [3.5 +/- 1.3 to 42 +/- 5.2% area at risk (AAR), Evan's blue/triphenyltetrazolium chloride staining]. IP (4 x 5 min) and cold ischemia (27 degrees C) reduced infarct size by 69 +/- 6.7% and 84 +/- 4.2%, respectively (n = 6, P < 0.01). In contrast, lower numbers of IP cycles did not alter infarct size. However, infarct sizes were distinctively different in mice from different genetic backgrounds. In addition to infarct staining, we tested cardiac troponin I (cTnI) as marker of myocardial infarction in this model. In fact, plasma levels of cTnI were significantly lower in IP-treated mice and closely correlated with infarct sizes (R-2 = 0.8). To demonstrate transcriptional consequences of cardiac IP, we isolated total RNA from the AAR and showed repression of the equilibrative nucleoside transporters 1 - 4 by IP in this model. Taken together, this study demonstrates highly reproducible infarct sizes and cardiac protection by IP, thus minimizing the variability associated with knot-based coronary occlusion models. Further studies on cardiac IP using transgenic mice may consider this technique.