Mechanism of the Cardioprotective Effect of Inhibition of the Renin-Angiotensin System on Ischemia/Reperfusion-Induced Myocardial Injury

抄録

Inhibition of the renin-angiotensin system (RAS) has been shown to be beneficial in providing cardioprotective effects in humans, but the mechanism of these effects is not well understood. In this study, we examined the effects and mechanism of RAS inhibitors on ischemia/reperfusion (IR)-induced myocardial injury in rats. Rats were randomly divided into five groups and treated with vehicle c, angiotensin converting enzyme inhibitor (ACE-I), angiotensin II type 1 receptor antagonist (AT₁-A), angiotensin II type 2 receptor antagonist (AT₂-A) or ACE-I plus bradykinin B₂ antagonist. Ten minutes after administration, the left main coronary artery was ligated for 45 min, and then reperfused for 120 min. IR-induced cardiomyocyte apoptosis was assessed by terminal deoxyribonucleotidyl transferase-mediated Dutp nick-end labeling (TUNEL) assay and confirmed by typical DNA laddering. Mitogen-activated protein kinase, extracellular signal-regulated protein kinase (ERK) and c-Jun NH₂-terminal protein kinase (JNK) activity in the ischemic zone were measured by an in vitro kinase assay. The duration of ventricular tachycardia (VT) during ischemia was reduced by AT₂-A and ACE-I, and increased by AT₁-A and ACE-I+icatibant. ACE-I and AT₂-A reduced apoptosis (by 54% and 53%) and infarct size (by 42% and 41%), while AT₁-A increased apoptosis (by 86%) and infarct size (by 45%). These changes were negatively correlated with the change in ERK activity. The effects of ACE-I on apoptosis and infarct size were abolished by the coadministration of icatibant. Apoptosis was correlated with the occurrence of VT (r=0.837, p<0.001). These results suggest that both the accumulation of bradykinin and inhibition of AT₂ receptor are cardioprotective against IR injury through the activation of ERK, but not JNK. (Hypertens Res 2001; 24: 179-187)