In this report we investigate the molecular mechanisms that contribute to tissue damage following ischemia and ischemia coupled with reperfusion (ischemia/ reperfusion) in the rat heart and kidney. We observe the activation of three stress-inducible mitogen-activated protein (MAP) kinases in these tissues: p38 MAP kinase and the 46-and 55-kDa isoforms of Jun N-terminal kinase (JNK 46 and JNK 55 ). The heart and kidney show distinct time courses in the activation of p38 MAP kinase during ischemia but no activation of either JNK 46 or JNK 55 . These two tissues also respond differently to ischemia/reperfusion. In the heart we observe activation of JNK 55 and p38 MAP kinase, whereas in the kidney all three kinases are active. We also examined the expression pattern of two stress-responsive genes, c-Jun and ATF3. Our results indicate that in the heart both genes are induced by ischemia and ischemia/reperfusion. However, in the kidney c-Jun and ATF3 expression is induced only by ischemia/reperfusion. To correlate these molecular events with tissue damage we examined DNA laddering, a common marker of apoptosis. A significant increase in DNA laddering was evident in both heart and kidney following ischemia/reperfusion and correlated with the pattern of kinase activation, supporting a link between stress kinase activation and apoptotic cell death in these tissues.

We investigated the effect of the adenosine deaminase inhibitors erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA) and coformycin on high-energy phosphate metabolism, tissue nucleotides and nucleosides, and recovery of contractile function in isolated, perfused guinea pig hearts. EHNA and coformycin (10 microM) improved postischemic recovery of contractile function approximately 85% and enhanced coronary flow rate in reperfused tissue approximately 40%. The protective effect of EHNA on recovery of contractile function was concentration dependent. Although adenosine (10 microM) increased coronary flow rate on reperfusion approximately twofold over vehicle, it failed to improve postischemic recovery of contractile function. EHNA and coformycin preserved cardiac ATP levels and increased endogenous tissue adenosine during ischemia. During reperfusion, these agents enhanced recovery of high-energy phosphates approximately twofold and potentiated adenosine release into the perfusate with concentration dependency. Furthermore, EHNA and coformycin reduced the extent of myocardial ischemia-reperfusion injury, as indicated by the approximately 55% reduction in creatine phosphokinase release. We conclude that inhibitors of adenosine deaminase attenuate myocardial ischemic injury and improve postischemic recovery of contractile function and metabolism through endogenous myocardial adenosine enhancement and ATP preservation.

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