The protective effect of angiotensin converting enzyme (ACE) inhibitor against ischemia/reperfusion injury has been demonstrated in animal models, however the effect of AT1 receptor antagonist is contradictory. The present study was designed to investigate the myocardial protective effects of the AT1 receptor antagonist irbesartan during myocardial ischemia/reperfusion in vivo.

Sprague-Dawley rats were subjected to a 45-minute left coronary artery ligation followed by a 2-hour re-perfusion. An inert vehicle (group I:n=14) or irbesartan (50 mg/kg/day:group II, n=12) was administered for 3 days before coronary occlusion. The ratio of the myocardial infarct area to the ischemic area at risk was assessed through triphenyltetrazolium chloride staining. Apoptosis was evaluated by analyzing DNA fragmentation and TdT-mediated dUDP nick end labeling staining. Western blot analysis was performed for MAP Kinases (ERK1/2 and p38) and Bcl-2 and Bax.

The ratio of the infarct area to the ischemic area at risk of group II was smaller than that of group I (42.6±2.7% vs. 64.1±4.6%;p<0.005). Agarose gel electrophoresis revealed discrete DNA laddering in the ischemic zone of group I, however DNA ladder formation was attenuated in group II. The expressions of ERK1 MAPK and Bcl-2 were increased in the ischemic area of group II compared to that of group I.

AT1 receptor antagonist was effective in reducing myocardial reperfusion injury in vivo. This effect can at least be partially attributed to the attenuation of cardiomyocyte apoptosis, and this anti-apoptotic effect appears to be related to the increased expression of Bcl-2 and alterations in MAP kinase signaling.