Response to ischemia-reperfusion injury in hypertrophic heart. Role of free-radical metabolic pathways.

Clinical and experimental evidence demonstrates that hypertrophied cardiac tissue is more sensitive to ischemic injury than is normal myocardium. Recent studies indicate that cardiac ischemia-reperfusion injury involves the generation of toxic oxygen free radicals. We used the spontaneously hypertensive rat (SHR) model, with its otherwise genetically identical control (the Wistar-Kyoto [WKY] rat), to investigate the potential role of enzymes that generate and detoxify oxygen radicals in the sensitivity of hypertrophied heart to ischemia and reperfusion. Because hypertension develops progressively with age in SHRs, we assayed xanthine oxidase, superoxide dismutase, catalase, and glutathione peroxidase at three different time points and found significant fluctuations at different ages. At age 26 weeks, physiological measurements demonstrated hypertension and increased sensitivity to ischemia and reperfusion, measured as significantly decreased left ventricular recovery after injury. At this age, xanthine oxidase, which may generate oxygen radicals, was significantly increased in SHR compared with WKY rats (p = 0.003). Superoxide dismutase, which is a principal step in oxygen-radical detoxification, was significantly lower (p = 0.044). These data suggest that differences in the constitutive levels of oxygen-radical metabolic pathways are different in hypertrophied myocardium, and it is suggested that this finding may play a role in the response of these hearts to ischemia-reperfusion injury.