Reduction of Myocardial Infarct Size in Rabbits by Ramiprilat

We wished to determine, using a novel specific antagonist of BK2, HOE 140, (a) if the angiotensin-converting enzyme (ACE) inhibitor, ramiprilat, reduces myocardial infarct size in a well-established animal model of ischemia/reperfusion with minimal coronary collater-alization, and (b) if the reduction in myocardial infarct size occurred through a bradykinin-dependent mechanism Saline vehicle, ramiprilat, HOE 140, or ramiprilat plus HOE 140 (n = 6 each group), was administered intravenously (i.v.) in intact animal preparations of experimentally induced acute myocardial ischemia. Anesthetized, open-chest rabbits were instrumented for measurement of systemic hemodynamics and left ventricular pressure (LVP), from which LV + dP/dtmax was derived. Animals were subjected to 30-min left main coronary artery occlusion (marginal branch) followed by 2-h reperfusion. Ramiprilat (50 μg/kg) or saline was administered before reperfusion, and rabbits receiving HOE 140 were pretreated before occlusion (1 μg/kg). In separate duration of action experiments (n = 6 each group), the above doses of ramiprilat or HOE 140 had significant vascular antagonism of sufficient duration against serial challenge with angiotensin I (AI) or bradykinin, respectively. After reperfusion, myocardial infarct size (IS) was determined by tetrazolium staining and expressed as a percentage of area at risk (AR). IS/AR% was significantly reduced in rabbits that received ramiprilat (20 ± 6%, p < 0.05) as compared with those that received saline (41 ± 6%), ramiprilat plus HOE 140 (47 ± 2%), or HOE 140 alone (43 ± 4%, mean ± SEM). AR as a percentage of total LV mass was not different between any of the four treatment groups. Tachycardia was observed during early reperfusion in each group treated with ramiprilat. Sustained hypotension (15–20 mm Hg) and a significant reduction in LV + dP/dtmax were evident in all groups throughout reperfusion, except in rabbits treated only with HOE 140, in which hemodynamics were maintained. The effect of ramiprilat to reduce infarct size is abolished by pretreatment with the specific bradykinin-2 antagonist, HOE 140, suggesting that bradykinin plays an important role in the myocardial protective action of ramiprilat.