Recovery of hypertrophied rat hearts after global ischemia and reperfusion at different perfusion pressures.

The ability to resist transient ischemia was studied in isolated hearts of 18 months old spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats. Both types of hearts showed optimal performance during the preischemic period when perfused at a diastolic perfusion pressure of 8.0 (WKY) and 13.3 (SHR) kPa. Hemodynamic recovery of WKY hearts during reperfusion at 8.0 kPa, following 45 min global ischemia, was satisfactory. coronary perfusion completely normalized, contractility (dPlv/dtmax) was slightly depressed and cardiac output returned, on the average, to 40% of the preischemic values. In contrast, hemodynamic function of SHR hearts reperfused at 13.3 kPa was greatly depressed, as evidenced by almost complete abolition of cardiac output, severe reduction of dPlv/dtmax and persistent underperfusion of the endocardial layers. In addition, the postischemic release of lactate dehydrogenase was retarded and enhanced. The release patterns of degradation products of adenine nucleotides showed a shift to the endstage products xanthine and uric acid. The enhanced vulnerability of the hypertrophied heart to ischemia was even more expressed when the SHR hearts were reperfused at 8.0 kPa. Postischemic function was characterized by electrical instability, loss of contractility and cardiac output, and noreflow in the endocardial layers. Persistent accumulation of lactate and degradation products of adenine nucleotides in the postischemic hearts are in line with the lack of reperfusion. The present results indicate that a detailed mechanistic explanation for the reduced ability to withstand ischemia of SHR cannot be based on differences in ATP content or an altered anaerobic glycolitic activity prior and during ischemia. It is suggested that a defect on the circulatory level, probably caused by enhanced reactivity of the coronary vessels towards ischemia-elicited factors, is responsible for the higher vulnerability of hypertrophied heart to an ischemia insult.