Endopeptidase inhibitors decrease myocardial ischemia/reperfusion injury in an in vivo rabbit model

Periods of ischemia followed by reperfusion of the ischemic tissue are associated with myocardial damage and ventricular arrhythmia. Angiotensin converting enzyme inhibitors limit the occurrence of these arrhythmias. The protective effects of angiotensin converting enzyme inhibitors may be due to inhibition of bradykinin (BK) degradation, rather than inhibition of angiotensin II formation. Other enzymes which catabolize BK include the endopeptidases EP24.11 and EP24.15. The purpose of this study was to determine if inhibitors of EP24.11 and EP24.15 decrease ischemia/reperfusion injury and if this protection is mediated by BK receptors. Rabbits were anesthetized and prepared for recording of cardiovascular parameters. The chest was opened and a left ventricular artery occluded for 30 min, followed by a 2-hr reperfusion period. Infarct size was determined using triphenyl tetrazolium chloride staining immediately after reperfusion. The enzyme inhibitors, ramiprilat, N-[1-(R,S)-carboxy-3-phenylpropyl]-Phe-pAB, and N[1-(R,S)-carboxy-3-phenylpropyl]-Ala-Ala-Phe-pAb, singly and in combinations were administered 3 min before reperfusion. Compared to saline (32.1 +/- 2.1), ramiprilat (18.3 +/- 2.8) and the EP inhibitors (14.4 +/- 1.4 for the combination) significantly decreased infarct size, with the greatest decrease occurring when all three inhibitors were combined (10.6 +/- 1.5). The protective effect of the EP inhibitors was blocked by the BK2 receptor antagonist, HOE 140 (30.1 +/- 2.6). Enzyme assays demonstrated EP24.11 and EP24.15 in the rabbit heart. We conclude that the EP inhibitors decreased ischemia/reperfusion injury by protecting BK from metabolism and that a combination of inhibitors provides superior protection to that given by a single agent.