Representative examples of a heart from each group.

<p>The infarcted region was delineated by perfusing the aortic root with 2,3,5-triphenyltetrazolium chloride (TTC); the region at risk was delineated by perfusing the aortic root with phthalo blue after tying the previously occluded artery. As a result of this procedure, the nonischemic portion of the left ventricle (LV) was stained dark blue and viable tissue within the region at risk was stained bright red (TTC positive), whereas infarcted tissue was light yellow or white (TTC negative). <b><u>Phase I</u></b> (<b><u>panel A</u></b>). Non-preconditioned <i>COX-2^+/+</i> and <i>COX-2^−/−</i> mice have similarly large infarct sizes. PC 24 h prior to MI results in a significant reduction in infarct size in <i>COX-2^+/+</i> but not <i>COX-2^−/−</i> mice. <b><u>Phase II</u></b> (<b><u>panel B</u></b>). Non-preconditioned B6 mice in naïve, vehicle-treated, and RO3244794-treated groups have similar infarct sizes. PC results in significantly smaller infarct sizes in naïve and vehicle-treated mice but not in RO3244794-treated mice. <b><u>Phase III</u></b> (<b><u>panel C</u></b>). Non-preconditioned <i>IP^+/+</i> and <i>IP^−/−</i> mice have similar infarct sizes. PC results in a significant reduction in infarct size in <i>IP^+/+</i> but not <i>IP^−/−</i> mice. Scale at bottom is in mm. Note the large, confluent areas of infarction spanning most of the thickness of the LV wall, with thin rims of viable subendocardial tissue. This pattern was characteristic of all 7 nonpreconditioned groups (groups I, III, V–VII, XI and XIII) and all 3 PC groups (PC in <i>COX-2^−/−</i> [group IV] and <i>IP^−/−</i> mice [group XIV] or pretreated with the RO compound [group X]). In contrast, mice subjected to the PC protocol exhibited small, sporadic areas of infarction, a pattern that was characteristic of all 3 PC alone WT mice (groups II, VIII and XIII) and of the mice with PC + vehicle (group IX).