Paracrine systems in the cardioprotective effect of angiotensin-converting enzyme inhibitors on myocardial ischemia/reperfusion injury in rats.

After transient episodes of ischemia, benefits of thrombolytic or angioplastic therapy may be limited by reperfusion injury. Angiotensin-converting enzyme inhibitors protect the heart against ischemia/reperfusion injury, an effect mediated by kinins. We examined whether the protective effect of the angiotensin-converting enzyme inhibitor ramiprilat on myocardial ischemia/reperfusion is due to kinin stimulation of prostaglandin and/or nitric oxide release. The left anterior descending coronary artery of Lewis inbred rats was occluded for 30 minutes, followed by 120 minutes of reperfusion. Immediately before reperfusion rats were treated with vehicle, ramiprilat, or the angiotensin II type 1 receptor antagonist losartan. We tested whether pretreatment with the kinin receptor antagonist Hoe 140, the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester, or the cyclooxygenase inhibitor indomethacin blocked the effect of ramiprilat on infarct size and reperfusion arrhythmias. In controls, infarct size as a percentage of the area at risk was 79 +/- 3%; ramiprilat reduced this to 49 +/- 4% (P < .001), but losartan had little effect (74 +/- 6%, P = NS). Pretreatment with Hoe 140, NG-nitro-L-arginine methyl ester, or indomethacin abolished the beneficial effect of ramiprilat. Compared with the 30-minute ischemia/120-minute reperfusion group, nonreperfused hearts with 30 minutes of ischemia had significantly smaller infarct size as a percentage of the area at risk, whereas in the 150-minute ischemia group it was significantly larger. This suggests that reperfusion caused a significant part of the myocardial injury, but it also suggests that compared with prolonged ischemia, reperfusion salvaged some of the myocardium. Ventricular arrhythmias mirrored the changes in infarct size. Thus, angiotensin-converting enzyme inhibitors protect the myocardium against ischemia/reperfusion injury and arrhythmias; these beneficial effects are mediated primarily by a kinin-prostaglandin-nitric oxide pathway, not inhibition of angiotensin II formation.

Isovolumic fractional rate of change of power: its applicability to assessment of ventricular performance in patients.

The ratio of the instantaneous isovolumic rate of change of power, normalized to instantaneous isovolumic power, appears to be an expression of physiologic and practical significance. This ratio, termed the isovolumic fractional rate of change of power, describes the capability of the ventricle to sustain, during isovolumic contraction, an acceleration of energy production relative to instantaneous rates of energy production. The expression is independent of assumptions of ventricular geometry, fiber orientation, symmetry of contraction or elasticity of muscle fibers. It was derived upon the basis of established principles of fluid dynamics. The expression serves in an integrative fashion by demonstrating a simple relation between characteristics of performance derived on the basis of fluid dynamics and those derived on the basis of muscle mechanics. In this study, the isovolumic fractional rate of change of power permitted distinction between patients with normal and abnormal ventricular performance (as characterized by the ejection fraction, mean velocity of circumferential fiber shortening and end-diastolic volume index) (P less than 0.01). The firm theoretical basis of the isovolumic fractional rate of change of power, and its demonstrated capability to permit identification of patients with normal or abnormal left ventricular performance, recommends it as a meaningful and useful hemodynamic expression.